Search your Article

Find the interesting articles for the rail experts

Articles

Contact . -
Posted 308 days Ago

PantoSystem Implemented for Siemens eHighway Project

Automatic Train Supervision

    The customer The German government has introduced several initiatives to promote overhead contact lines for trucks, also known as eHighway. This solution makes road freight transport more energy-efficient and environmentally friendly [1] . The latter point is especially important and urgent, as the German government´s climate protection plan calls for reductions in CO 2 emissions by 40% from the transport sector by 2030 [2] . Since 2018 the Ministry of Environment in Germany is funding field trials of the eHighway system on real highway [3] . The challenge is to ensure that operations of this solution can be scaled up, which the users will be much more numerous as well as diverse. To prepare for this, the experience and solutions from PantoInspect were called upon. Germany’s transport ministry has announced the scaling-up phase of eHighway in Germany. Analysis from among other Germany’s National Platform for New Mobility (NPM) show that electrifying 4.000 km of motorways by 2030 is a cost-effective way to reach the climate targets. Analysis also shows the potential benefits of expanding the concept to neighboring countries such as Denmark and Sweden [4] . Ultimately, as contact line technology is in global use and climate change is a global problem, the objective is to spread the eHighway concept to the rest of the world. Since the eHighway project has come very far in the technical development stage, the team is now part of Siemens Rail Infrastructure, the division responsible for electrification of rail, and now also road. The eHighway project started in 2010 with the aim of developing two main components, namely the catenary system for use on motorways and pantographs for electrified trucks. In 2017, Siemens Mobility was commissioned up to €15 million ($16 million) by the German state of Hesse to build a 10 km overhead contact line for electrified road freight transport on a motorway. The eHighway project, which was part of one of the first three test tracks on a German motorway, running between the interchange Mörfelden (close to the Frankfurt airport) and the interchange Weiterstadt (close to Darmstadt).   The challenges/problems An important task to the eHighway team was to find a pantograph monitoring solution that was suitable for electrified trucks that could be connected to the overhead contact line. It was important for the team to have a system that could inspect the pantograph of the trucks to ensure the availability of the catenary system on the highway. Therefore, the eHighway team was looking for an inspection system that could help them detect defect pantographs to prevent potential damage of the catenary system. They also needed an inspection system that could help them detect if the pantograph is in an operating state and check that wear on the carbon strips was within an acceptable range. In addition, making sure that the pantograph had no other mechanical deformations that could potentially damage the catenary system. One of the main challenges was to find a pantograph monitoring system for electrified trucks, which could be installed above an overhead line in the highway environment. Electrified trucks do not have metal wheels, and therefore two pantographs are needed to establish two electric poles from which they can draw the power from. For this reason, pantographs on electrified trucks normally have four carbon strips and two overhead contact lines, unlike a train pantograph, which usually has two carbon strips and a single overhead contact line. Since the pantographs on the trucks contain more parts, the monitoring system required more sensors and technology than the usual system used for railways to ensure that the truck can leave the electrified lane and connect to it again.   The solution To ensure a high availability of an eHighway, it is important that no defective or worn-out pantographs will contact the overhead contact line. Since the operator of an eHighway System has no direct influence on the technical condition of the participating vehicles, it is very important to monitor the technical conditions of the connected vehicles. Siemens Mobility evaluated the Pantoinspect sensor system at the eHighway test facility in Groß-Dölln because the combination of camera and laser scanner provides the necessary basic requirements, for checking eHighway pantographs. With the results of the laser scanner, the geometric dimensions of the pantograph can be verified and compared with the limit values ​​stored in the Backend Monitoring System. Critical wear and tear as well as geometrical deviations can be detected and transmitted to the operation and control center. If necessary, an operator can use the high-resolution camera images to verify a detected deviation and inform the user that his pantograph is damaged, and the use of the overhead line is no longer permitted. The evaluation showed, that for a later series production some potential for optimization will be necessary, however the main task can be fulfilled with the PantoInspect portfolio.   Werner Pfliegl, Product Management of Siemens Mobility GmbH, Germany said: “PantoInspect was chosen by the eHighway team because the company has the advanced technical expertise and many years of proven track record in supplying some of the major infrastructure owners and rail operators in the global railway industry. The PantoSystem was very beneficial for the eHighway project since the team considered it as an all-in-one system that combines both a camera system and a laser system”.   The eHighway team also believed that the software was very good at providing statistical data to give the operator a detailed overview of the condition of the pantograph. PantoInspect carried out a lot of research and development to build up a model which was able to recognize every part of the pantograph on electrified truck correctly. The triggering system was also challenging in the beginning since the data on the speed of the vehicle needed to be found through the laser scanner itself to trigger the camera system correctly. However, PantoInspect managed to make extensive modifications to both the hardware and software to meet the requirements of the eHighway project.  The laser scanning device of the PantoSystem helped the team to build 3D models of the pantographs, which detected the working condition of the pantograph. The camera system was also used as a backup system to help the operator verify potential pantograph defects. They also believe that the system can help the owners of electrified trucks to get data on worn-out pantographs and ensure less maintenance of the catenary system as well as reduce the risk of damaged overhead contact lines. Siemens Mobility sees many advantages in using the PantoSystem for future applications in both electrified trucks and railways to help prevent an installed technical base from any type of damage. The team also see many future potentials in using the PantoSystem on 1000s of km of electrified tracks on motorways to evaluate the condition of the catenary system and for maintenance purpose. The system could potentially also help the BAG (Bundesamt für Güterverkehr) to identify electrified truck with defect pantographs, during their regular inspections, and thereby maximize safety on the highways. The PantoSystem can help Siemens offer a complete solution which includes both the identification of trucks as well as detection of defect pantographs, and thereby add great value to the company. This fits very well with PantoInspect´s vision of creating environmentally friendly solutions for both electrified railways and trucks.     About PantoInspect PantoInspect was the first company world-wide to develop an automated pantograph inspection system, in partnership with Banedanmark, the Danish railway infrastructure owner, around 2008. Today, PantoInspect is one of the world’s most recognized and respected brands and a market-leading manufacturer and supplier of automated and real-time Wayside Pantograph Monitoring systems to the global Railway industry. We have supplied several pantograph monitoring systems to some of the world’s leading infrastructure owners and rolling stock operators such as Deutsche Bahn, RATP, Infrabel, Sydney Trains, Network Rail, and TRA.     PantoInspect  Titangade 9C Copenhagen 2200, Denmark www.pantoinspect.com Email: contact@pantoinspect.com Tel: +45 3318 912       [1] https://www.bmvi.de/SharedDocs/EN/Dossier/Electric-Mobility-Sector/electric-mobility-sector.html [2] https://www.oeko.de/fileadmin/oekodoc/Climate-friendly-road-freight-transport.pdf [3] https://ec.europa.eu/jrc/sites/jrcsh/files/20201028_eu-hgv-workshop_sue_public.pdf [4] https://www.linkedin.com/posts/steen-n%C3%B8rby-nielsen-5736886_tysklands-transportministers-klimaplan-for-activity-6732401194108620800-6Ybn 

Read Full Article

Esat Kepenekli -
Posted 293 days Ago

A Solution to the Impacts of Climate Change on Rail Infrastructure

Rail Tracks

The ability to detect the presence of a train on a particular stretch of track is a key enabler for automatic signalling, and hence modern train control. There are two types of technology generally used for train detection, a track circuit or an axle counter. Track Circuits also have a side function (usually without any commitments) to detect complete rail breaks to an extent with the employed impedance bonds, but they are not able to catch many of the broken rail cases, and the recent trend is to use axle counters instead of track circuits. There are many benefits of using axle counters in comparison to track circuits, like lower life-cycle costs, higher reliability, and better management of long sections. It should be noted that the widespread use of axle counters may provide great benefits for interlocking, however, the axle counters do not provide any information at all for whether the rail physical condition is in a safe state for train traffic or not. This means that when we start using axle counters, verification of rail condition with an additional monitoring system becomes vital to know whether there are any defects in the rails. If this aspect is neglected somehow, it seems quite likely that this can lead to disastrous consequences both for ASSET & PASSENGER SAFETY. The World’s Best Railway Infrastructure Owners are aware of the RISKS and they are searching for an Innovative & Accurate SOLUTION to the possible “Broken Rail” issues. Broken Rail Detection (BRD) systems are being offered to close the safety gaps related to the rail integrity monitoring aspects. And, early detection of rail flaws is being more vital each day, due to increased speeds in rail transportation, either for passenger or freight trains. If track circuits are used at a railway line, it is surely needed to deploy a supportive BRD system to close the safety gaps, however, if axle-counters are used, a reliable BRD system definitely becomes a “MUST-HAVE” for safe rail transport operation. The rail-mounted RailAcoustic® solution validates the health of the rail, identifies any breaks as soon as it occurs, and accordingly notifies the rail status immediately for the train dispatcher. RailAcoustic® thus increases throughput as tracks can be verified for operation instead of being blocked for days due to derailment accidents that can also have severe consequences. RailAcoustic® is designed for easy installation and track maintenance through the clamp mechanisms attached to the rail bottom without opening any holes or drilling on the rails. Its receivers identify even the partial rail cracks before a conventional track circuit could detect an electrical disconnect in the rail. Any complete break or a major partial break in the rail can be identified with a very accurate location within 100 m precision for safe train operation and ease of track maintenance. Rail-mounted RailAcoustic® components report to the back-office system to verify any detection. Messages are then passed to the signaling system or train control to take immediate action on the approaching or next trains passing the located breaks. This way, RailAcoustic® offers a near real-time detection and verification of breaks in rails – for safer and more profitable operation. The RailAcoustic® technology is demonstrated at High-Speed-Rail (HSR). The system is successfully in operation on a 90 km double-track stretch of the TCDD Konya High-Speed line, since 2018. Now, the installation and commissioning of the system continue for an 11 tunnel slab-track part (37 km) of the Sivas High-Speed line, to be integrated into the Siemens-provided CTC system. It is a proven, supportive, safety “enhancement” tool that does not need a SIL Certification in the short term, since it is not a component of mainline signalling but rather a very critical safety improvement for monitoring the RAIL and TRACK CONDITION. It solves a very critical issue in the railway industry with its methodology patented in the US, EU, China, Japan, India & Turkey, and has a great technical potential in the global rail industry subject to potential collaboration opportunities in different territories with diverse market needs. It has train monitoring abilities, which railway operators can benefit a lot. It is a result of 10 years-long research and development efforts that had been put in operation after extensive acceptance tests during the trial and commissioning phases of the client. The technology is unique and does not have any reasonable solution alternatives around the world offering a complete and stand-alone solution for high-speed railway lines, modernized conventional lines, and metro lines especially with continuously welded rails and limited ballast rock contact at the rail bottoms. Actually, as per the new approach with increased speed expectations in rail transport; it is obvious that a train should not be released to a line before being sure that especially the close segments of the tracks are safe for traffic. Only, then after "verifying the health status of rails and tracks", the interlocking and signalling come up to the fore, for a safe train presence monitoring and plotting of a route!  RailAcoustic® detects defects such as complete rail breaks and partial rail cracks, as well as other abnormalities like ballast washouts, floods, and landslides  The system 7/24 continuously senses: Partial Cracks on the Rails Complete Rail Breaks Significant Internal Defects Train Flat-Wheels Train Movement (with precise Speed info) Rail & Environmental Temperature Floods Landslides Washouts Buckled Rails Derailed Cars (only for low-speed freight rolling stock) The inventor and manufacturer of the system is Enekom, a technology company that is ready to be in collaboration with any parties, to enhance the safety of railways for protecting the assets and people. Please contact for further information: Esat Kepenekli – Contract and Commercial Manager Cell: +90 - 537 609 6498 (WhatsApp) Email: esatkepenekli (at) enekom.com.tr

Read Full Article

Deepu Dharmarajan -
Posted 209 days Ago

 CH25 | Modern Train Control Systems

CBTC

1. ‘Communication’  Based Train Control Systems Train control has advanced from conventional fixed block system to moving block technology during the last three decades. Many highly dense cities realized the need for moving commuters in a large scale, especially during peak hours and frequent train operation under 3min or less is inevitable.. This is often referred as Headway among the Technical diaspora. Headway can be put it in simple words “The theoretical time separation between two Trains travelling in the same direction on the same track. It is calculated from the time the head-end of the leading Train passes a given reference point to the time the head-end of the following Train passes the same reference point”  It is possible to achieve tight 3 min headway with the help of automatic signalling ,however this is possible at the expense of  large amount of signalling asset maintained and less safety .Not forgetting the fact that Automatic train Protection system can be implemented for  safety enforcement but large number of standalone ATP system are getting obsolete  (Example :Hitachi L10000) within next decade .large scale greenhouse gas emission reduction also boosted the requirement for large scale passenger and freight movement with utmost safety and energy efficiency .Thanks to  Paris agreement often referred as Paris Accords adopted in 2015 .Headway requirements are relatively low for Mainline and freight however the need  for enhanced  safety and  efficiency are ever growing .There are pros and cons for the most popular train control systems . 2. Communication Based Train control System (CBTC) As per Institute of Electrical & Electronics Engineers (IEEE 1474 ) CBTC is a “A continuous automatic train control system utilizing high-resolution train location determination, independent of track circuits; continuous, high capacity, bidirectional train-to-wayside data communications; and trainborne and wayside processors capable of implementing vital functions” They do possess the following characteristics Determination of train location, to a high degree of precision, independent of track circuits. A geographically continuous train-to-wayside and wayside-to-train data communications network to permit the transfer of significantly more control and status information than is possible with conventional systems. Wayside and train-borne vital processors to process the train status and control data and provide continuous automatic train protection (ATP). Automatic train operation (ATO) and automatic train supervision (ATS) functions can also be provided, as required by the particular application It is not necessary that train shall be in unattended mode (driverless) to be identified as a CBTC. Any system that performs the above-mentioned functionality can be identified as a Communication Based Train Control System. Even though IEEE definition didn’t expect the need for a secondary train detection system, majority of the suburban network make use of a secondary Train detection system such as Track circuits or Axle counter for the degraded mode of operation in case the complete loss of communication. CBTC is mentioned as the train control system used in urban mobility  per IEEE definition rest of  this article ,even though European Train Control System or Positive train Control System also based on wayside to train communication. 3. Utilisation of Moving Block in CBTC Conventional railway system works on Fixed block system where each blocks are defined and separated with safe distance(braking distance)   with safety margin  and only one train possible in a longer block at a time and the leading  train has to clear the block before following train can occupy the block.Where as in moving block  train as a “moving block “ maintain safe distance based on braking curve with a safety margin .Refer below figure to identify the difference. There is an article  with comparison is posted in RailFactor ,and detailed comparison between traditional fixed block and moving block is out of scope for this article. Fig 1: Traditional Fixed Block System Fig 2: Moving Block System 4. European Train Control System (ETCS)   Evolved from the need for economic integration of the European Union for inter operation of their Trains .There were different signalling principles ,’non standardized ‘ signalling equipment existed in conventional system giving nightmare to operate between boarders with multiple train borne  systems(Turn off and Turn On )  to cross the boarder ,even crew were needed to change during boarder crossing  irrespective of same gauges between boarder. A technical specification for interoperability was embraced by the European parliament and the council of Union on the interoperability of the European rail system in accordance with the legislative procedure. Major Rail System providers from Europe known as Unisig companies under European Union Agency for Railways   jointly produced the rules  described in ‘Subsets”  .So far ETCS has five  levels (Application Level 0, Level NTC ,Level 1 ,Level 2 and Level 3)  as described in SUBSET-026-2 . Global System for Mobile Communications-Railway(GSM-R) is the  mode of data transmission between train and regulation centres (Wayside and Train borne) for ETCS Level 2 . Considering the fear that next 10 years will phase out the GSM-R  and various ETCS Level 2  implementation planned will impact.It could be implemented  with Long Term Evolution (LTE)  digital Radio System.LTE is normally regarded as 4G protocol  and the Future Railway Mobile Communication System (FRMCS) is considering to move something similar to 5G. Note :- European Rail Transport Management System ( ERTMS) include ETCS +GSM-R 5. Positive Train Control System (PTC) A communication-based Train monitoring and control system with a train protection system originated for the North America. As defined by AREMA (The American Railway Engineering and Maintenance of Way Association ) a Positive  Train Control System has the primary characteristics of Safe Train Separation to avoid train collision ,Line speed Enforcement ,Temporary Speed Restrictions ,Rail worker safety and Blind spot monitoring .As published in Digital Trends PTC work by ” combining radio, cellular and GPS technology with railway signals to allow trains to identify their locations relative to other trains on the track “Concept wise”  in a way PTC and ETCS are same. 6. East Japan Train Control (EJTC) Classified as four levels from Level 0 to Level 3 .Level 0 make use of an Automatic Train Stop device (ATS-S)  to prevent collision .This has been replaced with Automatic Train Stop device Pattern Type (ATS-P) in Level 1 addressing the weakness in ATS-S .New development with EJTC Level 3  make use of radio transmission and train itself detect its location and communicate with other trains .EJTC Level 3 is named as Advanced Train Administration and Communication System ( ATACS )  using Autonomous Decentralized System (ADS)  Technology. ADS technology is considered as most innovative modern technology for smart trains by Dr. Kinji Mori from Japan. This decentralized system composed of modules designed to operate independently capable of interacting each other to achieve the over all goal of the system. This innovative design enables the system to continuously function even when the event of components (modules ) failures .This plug and play module also enable  to replace the failed module while the overall system is still operational. Refer Figure 3  for message passing in an autonomous decentralized system.                Fig 3: Architecture for Autonomous Decentralized System      ADS  is a decoupled architecture where each subsystem communicates by message passing using shared data fields .Uniqueness of ADS system is that it doesn’t contain a central operating system or coordinator. Instead of that each subsystem manages its own functionality and coordination with other subsystems. When a subsystem needs to interact with other subsystems it broadcasts the shared data fields containing the request to all other subsystems. This broadcast does not include the identification or address of any other subsystem. Rather the other subsystems will, depending on their purpose and function, receive the broadcast message and make their own determination on what need to be done with it or ignore. Data transmission can be carried out by Enterprise Service Bus (ESB) .It operates in the autonomous decentralized system 7. Chinese Train Control System(CTCS) Largely based on ETCS except CTCS has Six Levels. China has a large rail network constitutes of several types of rail network such as High Speed, conventional, passenger and freights and realized the dire need for standardization, that is the basis for CTCS. Like ETCS ,CTCS also make use of balises on CTCS Level 2 and Level 3 .However Wuhan -Guangzhou high speed line uses ETCS Level 2 .China From year  2016 onwards  all metro lines in China are required to utilise LTE as the basis of their communications network. 8. Definition Standards for CBTC and ETCS This section depicts the major requirement specification for both the technology .Its recommended to refer these standards . In further chapters will cover case study and standard references for subsystems for each  elements to build a ETCS and CBTC systems . ETCS (All Levels) -ERA UNISIG EEIG ERTMS USERS GROUP SUBSET-026 - System Requirements Specification SUBSET -027 - FIS Juridical Recording SUBSET -034 - Train Interface FIS SUBSET-035 - Specific Transmission Module FFFIS SUBSET-036 - FFFIS for Eurobalise SUBSET-037 - EuroRadio FIS SUBSET-038 - Offline Key Management FIS SUBSET-039 - FIS for RBC/RBC handover SUBSET-044 - FFFIS for Euroloop SUBSET-047 - Trackside-Trainborne FIS for Radio infill SUBSET-056 - STM FFFIS Safe time layer SUBSET-057 - STM FFFIS Safe link layer SUBSET-058 - FFFIS STM Application layer SUNSET-098 - RBC-RBC Safe Communication Interface SUBSET-100 - Interface "G" Specification SUBSET-101 - Interface "K" Specification SUBSET 114 - KMC-ETCS Entity Off-line KM FIS SUBSET-137 - On-line Key Management FFFIS ERA_ERTMS_015560 - ETCS Driver Machine Interface   CBTC IEEE 1474.1 - Communications-Based Train Control (CBTC) Performance and Functional Requirments IEEE 1474.2 - User Interface Requirments in Communications-Based Train Control (CBTC) Systems IEEE 1474.3 - Recomended Practice for Communication-Based Train Control (CBTC) System Design and Functional Allocation IEEE 1474.4(Draft) - Recomended Practice for Communication-Based Train Control (CBTC) System IEEE 1482.1 - Rail Transite Vehicle Event Recorders IEEE 802.11 - IEEE Standard for Information Technology — Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks — Specific Requirements IEEE 29148 - Systems and software engineering - Life cycle processes - Requirements engineering - IEEE Computer Society IEEE 828 (Configuration Management ) - IEEE Standard for Configuration Management in Systems and Software Engineering IEEE 12207 (Software Life Cycle Process) - Systems and software engineering — Software life cycle processes IEEE 15288(System Life Cycle Process) - Systems and software - Systems life cycle processes IEEE 24748 (System &Software Engineering ) - Systems and software engineering — Life cycle management IEEE 802.3 (LAN Interface) - IEEE Standard for Ethernet 9. Comparison between CBTC and ETCS As mentioned before CBTC is based on Institute of Electrical & Electronics Engineers (IEEE) defined requirements where as ETCS is based on Subsets from ERA * UNISIG * EEIG ERTMS USERS GROUP.Refer Below table  for some of comparison between CBTC and ETCS solution. 10. Selection of System (food for thought !) It is also vital to select the best suitable solution for the rail network, especially brownfield based on your operational needs, track alignment, type of rollingstock operating on the line, whether track is laid on viaduct /at grade or Tunnel. Sometimes it could be tricky. Let me explain a complex scenario of a suburban network, with varying distance between stations which  could be in between  1km to 25km .It is currently operating with a fixed block system operating 12 Trains Per hour during peak time and 7 Trains per hour on non-peak hours and the  future patronage for the next 50 years are identified as 25- 28 train per hour during peak and 12 Trains during  non-peak hours  . Track is laid on Tunnel for some sections, and majority are either on ground  or viaduct /bridges. Network need to operate long freights on non-peak hours  which cannot be fitted with trainbourne equipments .It also shares main land trains with similar scenario on non peak hours . Network  has active level crossing  through out  the network .Below table detail some of the ideal solution in terms of cost (especially when many long sections are present ,implementing and maintaining  a DCS /Wifi will be expensive ) .What do you select as the ideal  solution in this scenario ?

Read Full Article

Suman Pathak -
Posted 114 days Ago

Basic of MEP

General

  Basic of MEP MEP, or mechanical, electrical, and plumbing engineering, are the three technical disciplines that encompass the systems that allow stations/building interiors to be suitable for human use and occupancy. MEP construction must require all types of commercial, residential, and industrial purposes where services and facilities are required. MEP consists of installing air conditioning systems, water supply & drainage systems, firefighting systems, electrical power, and lighting systems including transformer substations and emergency power generators, fire protection and alarm systems, voice & data systems, security access, and surveillance systems, UPS, public address systems, Mast antenna TV system, and building management systems. MECHANICAL WORKS IN MEP PROJECT In MEP, major works are to be handled by Mechanical people because of HVAC or air conditioning system and that has piping work for cold and hot water, fabrication works for ducts, dampers and controllers, thermal/cold insulation works, and erection of machines like chiller unit, air handling units, grills, diffusers, etc. along with works of Drinking water, Drainage, and Sewerage systems. Other important Mechanical works are Firefighting works that included piping, sprinklers, and Pumps. ELECTRIC WORKS IN MEP PROJECT Electric works mainly included Electrical Power and Lighting but others like Transformer substations, Emergency power, UPS/Central battery, Voice/Data communication, TV, Security systems like CCTV surveillance system, Access control System, Public address system, Building management system (BMS), Fire alarm system, Surge Protection system, and Lightning protection system. PLUMBING WORKS ON MEP PROJECT Plumbing is a system of pipes and fixtures installed for the distribution and use of potable (drinkable) water, and the removal of waterborne wastes. It is usually distinguished from water and sewage systems that serve a group of buildings or a city.

Read Full Article

Deepu Dharmarajan -
Posted 469 days Ago

CH1 | THE PURPOSE OF SIGNALLING

Signalling

SIGNALLING BOOK | CHAPTER 1 CONTENTS 1.Introduction 2.The Problems to be Solved 3.Basic Requirements 4.Lineside Signals 5.The Absolute Block System 6.Interlocking of Points and Signals 7.Single Lines 8.Further Developments 1. INTRODUCTION In general, the railway traveller assumes  that  his  journey  will  be safe. This  high  standard of safety which is taken for granted is the result  of  a  long  history  of  development.  As human errors and deficiencies in safety systems become evident, often as a result  of  an accident, improvements are made which are then incorporated into new generations of equipment. This is certainly true of railway signalling. It also appears to  be  a continuing  process.  We have not yet reached the situation where absolute safety can be assured. It is useful to start by looking back at some of the early history of signalling development. In the early days of railways, trains were few and speeds were low. The risk of a serious collision between two trains was minimal. Better track and more  powerful  locomotives allowed trains to run faster (requiring greater stopping distances). Railway traffic increased, requiring more and larger trains. The risks thus became greater and some form of  control over train  movements  became  necessary.  The need  for railway signalling had been identified. 2. THE PROBLEMS TO BE SOLVED 2.1 Collision with a Preceding Train When one train follows another on to the same section  of  line,  there  is a  risk  that,  if  the first train travels more slowly or stops, the second train will run into the rear of the first. Initially, trains were separated using  a system of  "time  interval"  working,  only  permitting a train to leave a station when a prescribed time had elapsed after the departure of  the previous train. Although this reduced the risk  of  collisions, a minimum safe distance between trains could not be guaranteed. However, in the absence  of  any proper communication between stations, it was the best that could be achieved at that time. 2.2 Conflicting Movements at Junctions Where railway lines cross or converge, there is the risk of two trains arriving simultaneously and both attempting to enter the same portion of track. Some  method  of  regulating  the passage of trains over junctions was therefore needed. This should ensure that one train is stopped, if necessary, to give precedence to the other. 2.3 Ensuring that the Correct Route is Set Where facing points are provided to allow a train to take alternative routes, the points must be held in the required position before the train is allowed to proceed and must not be moved until the train has completely passed over the points. Depending on the method of point operation, it may also be necessary to set trailing (i.e. converging) points to avoid damage to them. 2.4 Control of Single Lines Where traffic in both directions  must  use  the same single  line,  trains  must  not  be allowed to enter the single line from both ends at the same time. Although this could in theory be controlled by working to a strict timetable,  problems  could  still  arise if  trains were delayed or cancelled. 3. BASIC REQUIREMENTS We therefore have the basic requirements of any railway signalling system. The method of implementation has changed over the years but the purpose remains the same:- To provide a means of communicating instructions to the driver (signals) to enable him to control his train safely according to the track and traffic conditions ahead. To maintain a safe distance between following trains on the same line so that a train cannot collide with a preceding train which has stopped or is running more slowly. To provide interlocking between points and the signals allowing trains to move over them so that conflicting movements are prevented and points are held in the required position until the train has passed over them. To prevent opposing train movements on single lines. All the above requirements place restrictions on train movements, but it is vital that the signalling system will allow trains to run at the  frequency  demanded  by  the  timetable  to meet commercial requirements. This must be done without reduction of safety below an acceptable level. Signalling involves not only the provision of  equipment  but the adoption  of  a consistent  set of operating rules and communication procedures which can be understood and implemented by all staff responsible for railway operation. 4. LINESIDE SIGNALS It will probably be evident that the decisions regarding the movement of two or more trains over any portion of the railway can only be made by a person on the ground who has sufficient knowledge of the current traffic situation. His decision must be passed on to the driver of each train passing through his area of control. In the early days railways employed policemen whose duties would include the display of hand signals to approaching trains. As the policemen also had many other duties, it soon became impractical for them to be correctly positioned at all times. Fixed signals of various designs, often boards of different shapes and colours, were provided. The policeman could then set these and attend to his other duties. The simplest signals would only tell a driver whether or not he could proceed. From this evolved a standard layout of signals at most small stations; a "home" signal  on the approach side controlling entry to the station and a "starting" signal  protecting  the section of line to the next station. Between these signals, each train would be under the direct control of the policeman. These signals could give only two indications,  STOP  or  PROCEED. They therefore became collectively known as "stop" signals. As line speeds increased, "distant" signals were introduced which gave advance warning of the state of stop signals ahead. A distant signal could be associated with one or more stop signals and would be positioned to give an adequate braking distance to the first stop signal. It could give a CAUTION indication to indicate the need to stop further ahead or a CLEAR indication, assuring the driver that the stop signal(s) ahead were showing a proceed indication. With the addition of distant signals, trains were no longer restricted to a speed at which they could stop within signal sighting distance. It is important to understand the difference between stop and distant signals. A train must never pass a stop signal at danger. A distant signal at caution can be passed but the driver must control his train ready to stop, if necessary, at a stop signal ahead. The earliest signals were "semaphore" signals (i.e. moveable boards). To enable operation at night, these often had oil lamps added. With the advent of reliable electric lamps, the semaphore signal became unnecessary and a light signal could be used by day and night. Red is universally used as the colour for danger while green is the normal colour for proceed or clear. Initially, red was also used for the caution indication of distant signals but many railway administrations changed this to yellow so that there was no doubt that a red light always meant stop. If necessary, stop and distant signals can be positioned at the same point along the track. Alternatively, certain types of signal can display three or more indications to act as both stop and distant signals. 5. THE ABSOLUTE BLOCK SYSTEM Although time-interval working may seem crude, it is important to remember that nothing better was possible until some means of communication was invented. The development of the electric telegraph made the Block System possible. On many railways, time-interval working on double track lines is still the last resort if all communication between signal boxes is lost. 5.1  Block Sections In the Block Signalling system, the line is divided into sections, called "Block Sections". The Block Section commences at the starting signal (the last stop signal) of one signal box, and ends at the outermost home signal (the first stop signal) of the next box. With Absolute Block working, only one train is allowed in the Block Section at a time. The signalman may control movements within "Station Limits" without reference to adjacent signal boxes. The accompanying diagram shows a block section between two signal boxes on a double track railway. To understand the method of working, we will look at the progress of a train on the up line. Signalbox A controls entry to the block section but it is only signalman B who  can see a train leaving the section, whether it is complete (usually checked by observation of the tail lamp) and who thus knows whether or not the section is clear. Signalbox B must therefore control the working of the UP line block section. Similarly, signalbox A controls the DOWN line block section. 5.2 Block Bell The signalmen at each end of a block section must be able to communicate with each other. Although a telephone circuit is a practical means of doing this, a bell is normally used to transmit coded messages. It consists of a push switch ("tapper") at one box, operating a single-stroke bell at the adjacent box (normally over the same pair of wires). The use of a bell enforces the use of a standard set of codes for the various messages required to signal a train through the section and imposes a much greater discipline than a telephone, although a telephone may be provided as well, often using  the same circuit as the block bell. 5.3 Block Indicator This provides the signalman at the entrance to the  section with a continuous visual indication of the state of the section, to reinforce the bell codes. It is operated by the signalman at the exit of the block section. Early block instruments were "two position" displaying only two indications;  line clear and line blocked. Later instruments display at least 3 indications. The most usual are:- Line clear Giving permission to the rear signalman to admit a train to the section. Normal or Line Blocked Refusing permission. The signalman at the entrance to the section must maintain his starting signal at danger. Train on Line There is a Train in the block section. 5.4 Method of Working When signalbox A has an UP train approaching to send to box B,  the signalman at A will offer it forward to box B, using the appropriate bell code (so that signalman B knows what type of train it is). If the signalman B is unable to accept the train for any reason, he will ignore A's bell, and leave the UP line block indicator at "Normal". If he is able to accept the train, signalman B will repeat the bell code back to box A, and change the indication to "Line Clear". When signalman A sees  his  block  repeater go to "Line Clear", then he can clear his starting signals to admit the train to the section. When the train actually enters the section, signalman A sends the "Train Entering Section" bell code to box B. Signalman B will acknowledge this by repeating the bell code back to A, and turning the block indicator to "Train on Line". When the train leaves the block section at B, the signalman  there checks  that it is complete by watching for its tail lamp. He then turns his block indicator to "Normal" again.  He also sends the "Train out of Section" bell code to A, which A acknowledges by repeating it back. The system is now back to normal, ready for the next train. On multiple track railways, a pair of block instruments as above is required for each line. 5.5 Extra Safeguards The basic three-position block system, as described, relies on the correct sequence of operations for safety. A signalman could forget that he has a train in section and turn the indicator to "line clear", allowing a second train in. A detailed record (the train register) is kept of the actual times of train arrival and departure, and the times at which the bell signals are exchanged. In most places, additional safeguards have been added to the basic system. An  electric lock on the starting signal will prevent it being operated unless the block indicator is at line clear. Track circuit occupation may be used to set the block  instruments to ''Train on Line" if the signalman forgets to do so. Electric locking may also be used to ensure that signals are operated for one train movement only and replaced to danger before another movement is permitted to approach. Although it is unusual for absolute block working to be installed on any new signalling installation today, there are many railways on which it is in widespread use. The  block system, by ensuring that only one train may occupy a section of line at any time, maintains a safe distance between following trains. 6. INTERLOCKING OF POINTS AND SIGNALS On all early railways, points were moved by hand levers alongside the points. They could therefore be moved independently of the signals controlling the movement of trains. A great improvement in safety (as well as efficiency) was possible by connecting the point switches via rodding to a single central control point (the signal box). Similarly the signals could also be operated by wire from levers in the signal box. With the control of points and signals all in one place the levers  could be directly interlocked with each other. This had the following benefits:- Signals controlling conflicting routes could not be operated at the same time. A signal could only be operated if all  the points were in the correct position. The points could not be moved while a signal reading over them was cleared. In early signalling installations, all point and signal operation, together with any interlocking, was mechanical. Although it was a great technological advancement to be able to control a station from one place, the effort required to operate the levers restricted control of points to within about 300 metres from the signal box and signals up to about 1500 metres. At large stations, more than one signal box would often be necessary. The possibility still existed for a signalman to set the points, clear the signal, the train to proceed and then for the signalman to replace the signal to normal. This could free the locking on the points before the train had completely passed over them. Signalmen's instructions usually required the complete train to pass over the points before the signal was replaced to danger. 7. SINGLE LINES On most single line railways trains are infrequent. It is not normally necessary for two trains to follow each other closely in the same direction. Single lines were therefore treated in the same way as a normal block section with the important extra condition that trains could not be signalled in both directions at the same time. To enforce this condition and also to reassure the driver that he could safely enter the single line, some form of physical token was used as authority to travel over the single line. On the simplest of systems only one token existed. This caused problems whenever the pattern of service differed from alternate trains in each direction. If the timetable required two trains to travel over the single line in the same direction, the driver of the first train would be shown the token (or train staff  as  it is commonly  known) to assure the driver that no other train was on the single line. His authority to enter the single line would however be a written ticket . The following train would convey the train staff. Although workable, this system would cause problems if trains did not work strictly to the timetable. A further improvement was to provide several tokens, but to hold them locked in instruments at either end of the single line. The instruments would be electrically interlocked with each other to prevent more than one token being withdrawn at a time. The one token could however be withdrawn from either instrument. If the single line block equipment fails, many railways employ a member of the operating personnel as a human token. The "pilotman", as he is usually known, will either travel with the train or instruct the driver to pass through the section. No other person may allow a train on to the single line. Operationally, this is the equivalent of the train staff and ticket system described earlier. 8. FURTHER DEVELOPMENTS The main functions of the signalling system had now been defined, although they were to be continuously improved as the available technology developed. All  signalling  systems would be required to maintain a safe distance between trains, interlock points and signals and thus prevent conflicting movements, and provide the necessary information so that the speed of all trains can be safely controlled. In recent years, the signal engineer has been asked to provide further facilities within the general scope of the signalling system. These include, train information to the operating staff, train information for passengers, detection of defective vehicles, identification of vehicles and the increasing automation of tasks previously carried out by humans. The technology exists to completely operate a railway without human intervention although the level of automation desirable for a particular railway is for that railway administration to decide. Factors such as cost, maintainability, reliability, staffing policy, passenger security and sometimes political considerations must be taken into account. In many cases the final decision on the type of signalling to be provided is outside the direct control of the signal engineer. However, he should always endeavour to provide the best possible information and propose cost-effective solutions to particular problems so that the best decisions can be made.

Read Full Article

Deepu Dharmarajan -
Posted 462 days Ago

CH10 | TRACK CIRCUIT BONDING

Signalling

TRACK CIRCUIT BONDING   CONTENTS   Introduction Fouling & Clearance Points Positioning of Insulated Joints Jointless Track Circuits Bonding of Rails Track Circuit Interupters  Other Information on Bonding/Insulation Plan NOTE: While these notes are based on the authors' understanding of railway signalling practice in New South Wales of Australia, they must not be taken to modify or replace any existing rules, instructions, or procedures of any railway administration. Where any apparent conflict exists, reference should be made to the appropriate documents produced by the administration of your Railway. This article will give fair bit of knowledge on bonding, there are numerous types of track circuits (FS2550, FS3000, CVCM, SDTC, TI21, MicroTrax). Bonding rules vary for these, and the respective manual shall be referred to. Bonding requirement for Axle counters is very limited (for Traction purpose only) and are out of scope for this article. 1. Introduction   A modem signalling installation will use many track circuits. The limits of each track circuit must be precisely defined, and the track circuit must be connected to operate safely and reliably, even through the most complex points and crossings. In many cases this will involve the installation of insulated joints, although jointless track circuits are available to suit many applications. An insulated joint is relatively simple to provide in jointed track. The fishplate and its bolts are insulated from the rail and an "end­ post", a piece of insulating material of similar shape to the rail cross section, is inserted between the rail ends. In welded rail, this operation is much more complex. Either the rail must be cut and an insulated joint inserted or a length of rail is removed and a pre-assembled joint in a section of rail is substituted. The rail is then welded. Both operations involve the adjustment of the rails to allow for internal stresses. After installation an insulated joint will generally be weaker than the rail on either side. Therefore, although insulated joints are essential, their position must be chosen correctly, and the number of joints minimized. In addition, it may be desirable to avoid joints in positions of greatest wear, vibration, or stress on the rails. The positioning of insulated joints may often be a compromise between the requirements for an ideal track circuit and the practicalities of permanent way construction and maintenance. For correct operation, the two rails of each track circuit must both be electrically continuous between all extremities of the track circuit. The rails must also be insulated from each other. This requirement is just as important through points and crossings as on plain line. There should be no position within a track circuit where a vehicle can be totally undetected. Each track circuit must operate reliably and must as far as is practical fail safe. Any normal failure mode should result in the track indicating occupation by a train. In areas where electric traction is employed, one or both rails will be used for the return traction current. The track circuit arrangement must permit an adequate traction current return path while maintaining safe operation of track circuits. In addition to the signalling plan, it is customary to prepare a plan showing the arrangement of the track circuits. Instead of a single line for each track, it will show each rail individually. Its main purpose is to show the bonding and insulation arrangements for all track circuits. In addition, it may show other useful information such as position of cable routes and locations, overhead structures, traction power supply connections, earth bonding and further details of the track circuit equipment.  2.      Fouling & Clearance Points Many insulated joints are positioned to prove clearance in the vicinity of points and crossings. The following terms will be used in these notes to describe the positioning of insulated joints. The fouling point is the position at which the extremity of a vehicle on one track is clear (by an adequate margin) of a movement on a converging line. The placing of an insulated joint at this position will not, however, ensure sufficient clearance. The clearance point is the position at which an insulated joint must be placed to ensure a vehicle stands beyond the fouling point. The distance of this from the fouling point will be determined by the longest overhang of all vehicles operating on the line. It follows that a joint which is intended to prove clearance must be positioned beyond the clearance point. although the signalling plan is not of adequate scale to show these joints accurately the track circuit bonding plan, or insulation plan, must be of a large enough scale to do so. If necessary, critical measurements must be taken from permanent way construction drawings. The limits of jointless track circuits cannot be precisely defined and cannot accurately determine clearance points. Even if jointless track circuit equipment is used through points and crossings, insulated joints will be needed to define clearance points and to electrically separate opposite running rails. 3.   Positioning of Insulated Joints   The positioning of insulated joints must fulfil all of the following requirements:- a) Within any track circuit, the two rails must always be of opposite. b) Unless adjacent track circuit signals employ different frequencies, the polarity (d.c. tracks) or phase (a.c. tracks) must be opposite on each side of all insulated joints. This is equally important whether the joint separates two track circuits or the two rails of the same track circuit. c) Where it is unavoidable to stagger block joints (i.e. they are not exactly opposite), the separation must be limited so that complete vehicles cannot remain undetected. d) Separation of a staggered pair of joints from an adjacent pair of joints (whether staggered or not) must not result in a vehicle being undetected. Critical clearance points cannot be defined by staggered. e) Minimum track circuit length must be greater than maximum vehicle wheel base. f) Maximum and minimum track circuit lengths must be within the specified range of operation of the type of track circuit. Most railways now employ a high degree of standardization of permanent way components. This will often restrict the position of insulated joints within points and crossings. Preferred positions must be used wherever possible to avoid additional cutting of rails and subsequent track maintenance. The use of these preferred positions will often result in joints being staggered. At a turnout, if there is a choice between joints in a high speed or low speed line, the low speed line is usually preferred. In cases where electric traction employs a single rail return, joints in plain line will usually be provided in one rail only. Pairs of joints will occur however in points and crossings and where it is desired to change the traction return rail from one side to the other. The above rules for staggering will still apply. In areas with double rail traction return, jointless track circuits must be used or joints must be provided in both rails, together with impedance bonds for continuity of traction current past the joint.   4. Jointless Track Circuits For adjacent jointless track circuits of the same type, no joints are necessary unless clearance points must be accurately defined. For replacement of signals and defining the end of an overlap, tolerances of 5-10 metres are usually acceptable. Adjacent jointless track circuits of the same type must be of different frequencies. Where a jointless track circuit adjoins a jointless track circuit of a different type, block joints will usually be needed due to different operating characteristics. A filter designed to operate with one type of track circuit is unlikely to discriminate correctly between signals of a different type of track circuit. Where any extremity of a jointless track circuit must be accurately positioned for clearance purposes, insulated joints must be provided. 5.  Bonding of Rails   Each rail must be bonded to give electrical continuity throughout the track circuit. The arrangement of bonding may be dependent on traction power supply arrangements. For fail safe operation feed/transmitter connections must be at one extremity of the track circuit and relay/receiver at the other. Between the feed and relay connections, the bonding must as far as possible be fail safe. If the rails are not welded together or otherwise bonded (e.g. for traction current) the signal engineer must provide adequate bonding throughout the length of the track circuit. The safest way of bonding the rails together is in series. On plain line this is the only practical method of bonding so no problems will arise. Within points and crossings, all track circuits will have additional branches which must also be bonded. All sections of a track circuit should still be bonded in series, but this may not be possible in all cases due to traction requirements. A certain amount of parallel bonding may be necessary. Figures 2 & 3   below demonstrate the difference between series and parallel bonding. In Figure 2, the rails in the turnout are parallel bonded. A break in any bond or rail in this section of track could leave a vehicle undetected - the track circuit will indicate clear when a train is standing on part of it. If the connections are rearranged as in the Figure 3, only very short sections of rail are now parallel bonded. Other than in these short sections, a break in a bond or a rail will cause the relay to drop, indicating an occupied track. Even in non-electrified areas, there will always be short branches of a track circuit which. cannot be connected in series (e.g. where the switch and stock rail adjoin). When the arrangement of track circuit bonding and insulation is being designed, the length of these branches should be kept as short as possible. 5.1  Non-electrified Areas It is usual, although not essential , to install insulated joints in both rails where electric traction is not used. In this case, series bonding should be employed throughout. To maximise the amount of series bonding, certain portions of rail through points and crossings may be common to two adjacent track circuits. In general, this should not cause a problem but in complex track layouts, the bonding and insulation must be checked very carefully to ensure that the use of a common rail between several nearby pairs of track circuits does not provide an electrical path for false operation of a track circuit and does not cause any track circuit to be shunted by trains outside its limits. Refer FIGURE 4 for a Track Circuit Sharing a common rail. 5.2.     Single Rail Traction Return   On many electrified lines, particularly those with a high voltage a.c. supply; traction return is via one rail only. The signal engineer still has exclusive use of the other rail. The two rails are normally designated the signalling rail and the traction rail. Of course, the signalling equipment must always use both rails. Track circuits connected in this way are described as single rail track circuits. The signalling rail will be series bonded. The traction rail must be connected to give the lowest impedance path back to the feeder station. Track circuits should be connected so that as much as possible of the traction rail bonding is in series. Often, however, parallel bonding must be accepted in the traction rail. A typical example of bonding for a single rail track circuit is shown on Figure 5. The signalling rail is connected to provide the maximum amount of series bonding. The traction rail shows a significant amount of parallel bonding. 5.3  Double Rail Traction Return   On Some lines, particularly those with d.c. traction, a lower supply voltage increases the traction current. This will often require both rails to be used for traction return.  Track circuits must therefore operate safely and reliably while sharing both rails with the much larger traction currents. To allow traction currents to pass conventional insulated joints, impedance bonds are used. Where two double rail tracks adjoin, the centre connections of the two impedance bonds are joined together. The ends of each coil are connected to the rails on either side. Where a double rail track circuit is of a jointless type, impedance bonds are not normally needed where tracks of the same type adjoin. At the end of a section containing a number of jointless track circuits, insulated joints are usually required and an impedance bond (resonated to the track circuit frequency) will be needed to pass the current around the insulated joint. Impedance bonds are also needed wherever the traction return must be connected to the supply at a feeder point and where adjacent roads are bonded together to reduce the impedance of the return path. Plain line track circuits are inherently series bonded.  Through points and crossings, however, if the double rail traction return is to be continuous, a proportion of parallel bonding is required. Although it prevents proof of continuity of the track circuit and its bonding, parallel bonding must be accepted as the only means of providing a low impedance traction return. Additional security is usually given by duplicating some or all of the rail-to-rail bonds (which of course will all be traction bonds and must consist of a suitably sized conductor).  Even in series bonded sections of rail, bonds or jumpers are often duplicated for reliability reasons. It must be remembered that maintenance routines must include regular checking of the integrity of these bonds because the disconnection of a single bond will not become evident as a track failure. Refer Figure 6 for Double Rail Track Circuit with Parallel bonding.    5.4.    Transition Between Single & Double Rail At the end of double rail sections, where they adjoin single rail track circuits, insulated joints will be required in both rails. An impedance bond will generally be needed for the double rail track. Its centre connection in this case will be bonded to the traction rail of the single rail track circuit. Refer Figure 7 for Typical Connections Between Single and Double Rail Track circuits. Where double rail tracks are in general use, even a small section of single rail return will increase the impedance of the traction return path. Single rail tracks in this situation are kept as short as possible. In some cases, two separate track circuits may be provided where a long track includes both points and plain line, even if one single rail track circuit could perform adequately over the total distance. 6. Track Circuit Interrupters   Track circuit interrupters are used to detect that a train has been derailed by a set of catch (trap) points by maintaining the track in the occupied state. The reason for this is that a derailed vehicle may be completely clear of the rails while still in a position which would be foul of other movements. If track circuit interrupters are provided, the following rules will generally apply to the track circuit bonding: - a)  The track circuit interrupter will be insulated from the rail upon which it is mounted. b) It will be bonded in series with the opposite rail to the one upon which it is mounted. c) Traction current should not pass through the track circuit interrupter. If mounted on a double rail track circuit, the interrupter must be connected in a separate circuit. A contact of the interrupter repeat relay must be included to cut the TPR circuit of its associated track. 7.  Other Information on Bonding/Insulation Plan   The bonding or insulation plan will often show other additional information such as:- a)  Position of overhead electrification structures. b) Bonding between overhead structures and traction return rails. c) Positions of locations, cable routes and signal structures.   Note : Please comment in the query section ,if you wish to discuss about  Bonding for Track Circuits like FS2500/FS3000, CVCM ,SDTC,TI21 etc on real layout . 

Read Full Article

Deepu Dharmarajan -
Posted 461 days Ago

CH11 | SIGNALS AND TRAINSTOPS

Signalling

Coming Soon....

Read Full Article

Deepu Dharmarajan -
Posted 461 days Ago

CH12A | CABLES

Signalling

CONTENTS         Introduction Signalling Cables Telecommunication Cables Power Cables Selection of Cable Type Methods of Termination Cable Routes Cable Construction Electrical Properties Cable Testing Data Cable Fiber Cables   INTRODUCTION Railway signalling now involves a wide range of equipment and techniques to transmit information, ranging from simple d.c. to carrier and data transmission. Associated with these is an equally wide range of interconnecting cables. Some are peculiar to railway signalling. Others are generally produced for telecommunications or general electrical purposes and have found applications within railway signalling. Refer Article Signalling Cable Standards on Rail Factor for a comprehensive list of cable standards, user of this article shall make effort to cross refer their current  local guideline/standard  in this regard.       2. SIGNALLING CABLES   Most lineside signalling circuits are d.c. or mains frequency a.c. Voltages are low, typically 24 - 120 volts. In some cases point machine can be 3 phase ,415/400 Volts ,3 wire system. Cables designed for conveying d.c. or low frequencies are generally far simpler than those for a.c. use. This is because the transmission of d.c. is far less demanding on the type and dimensions of the insulating materials and also on the construction of the cable. Under d.c. conditions the voltage drop along the cable conductor is the product of the current flowing and the resistance of the conductor. As long as the insulation material and its thickness is chosen such that its resistance is very high then it will have little or no effect on the voltage drop along the conductor. Although the electrical characteristics of most signalling cables will be similar, cable construction will vary according to the environment in which the cable is to be installed. The most common variants are:- 2.1 Internal wiring   This is usually flexible (stranded conductor) for easy installation along relay racks ,cable frame ,interlocking cabinets and cable ducts. The cable will generally be installed in a controlled environment so the sheath will not have to withstand such great changes in temperature, humidity and mechanical stresses as those installed outside. Many countries now have quite stringent requirements for the sheath material to satisfy fire regulations, the objective being to avoid emission of harmful gases in the event of a fire. Many existing internal cables have a PVC sheath. EVA (Ethylene Vinyl Acetate, otherwise known as Cross Linked Polyethylene) is often preferred now as it generally satisfies fire regulations. Some railways insist to use double sheathed insulation. Requirements for emission of smoke /and hazardous gas can be referred to IEC 61034-1/-2 and IEC60754-1 respectively. Similarly, IEC 60332-1 & IEC 60332-3 for flame test on Single wire and bunched wires respectively. UL1581 is an American Standard for electrical wires. Standard Size of wires are defined by AWG (American Wire Gauge)/European Or British Standards. Similar requirements exist for cables in tunnels and EVA sheathed cables are also used on underground railways. Internal cables are generally required as multicore cables (e.g. wiring between racks) and single core (individual circuits in interlockings and locations). Annealed Copper wires are used for electrical conductor compliant to IEC 60228(Australian AS/NZS 1574 & section 1&2 of 1125 ) 2.2 Lineside Cables Although these may carry similar circuits to the internal cables, they must withstand a more hostile environment. Typically, they will be installed in lineside troughs or buried and will be subject to changes in temperature and humidity, often lying-in waterlogged ground. Often UV Rays, oil, rodent and vermin will also be a problem. Individual conductors are insulated by an ethylene propylene rubber (EPR) compound/ while the outer sheath is polychloroprene (PCP) to give an oil resistant cable which will also withstand abrasion. If the cable requirement ask for UV Protection, Low Smoke Zero Halogen, Flame/Fire Retardant, carbon/iron/ wash plant liquid protection, outer sheath shall be selected accordingly . HDPE (High Density Polyethylene) cross linked polythene cover majority of such requirements. Most cables are multicore, to carry many separate signalling circuits. A single conductor will normally be adequate as the cable will not be subject to significant vibration once installed. Power cables are of similar construction but generally consist of two cores (for d.c. or single phase a.c. distribution and will generally have a stranded conductor due to the cross-section required. Some railways favour some form of armoured sheath (e.g. steel wire) for added mechanical protection. 2.3 On-track Cables Trackside electrical equipment is generally connected by cables across or under the ballast. Such cables must be strong and capable of withstanding considerable vibration. British Railway uses a flexible, multi-strand cable. Materials and construction are as for the lineside cables above, but the sheath is thicker, and the conductor is composed of a larger number of smaller strands (50/0.50mm).    Again, many railways prefer an armoured cable but this can also present problems with earth faults where the risk of damage to the cable is high. 3.TELECOMMUNICATION CABLES   Under a.c. conditions the inductance and capacitance of a cable can have a considerable bearing on the voltage drop and these factors become of major importance as the frequency increases. The capacitance of a cable pair or conductor will depend on the type and thickness of the insulation material. For a given material the thickness required for ac. transmission will generally be greater than for d.c. transmission. Suitable insulation materials for a.c. cables are dry air, paper and polythene. P.V.C. and rubber are not considered to be satisfactory, except in the case of low frequency cables such as 50Hz power. With multicore cables there is the additional problem of interference in one circuit due to the current in a neighboring circuit, commonly called "Crosstalk". The degree of crosstalk which may be encountered can depend on a number of different factors e.g. a) The frequency of the disturbing signal e. crosstalk increases with frequency (square waveforms, because of their high harmonic content are particularly troublesome). b) The magnitude of the current flowing in the disturbing i.e. crosstalk increases with the current. c) The position of the conductors in the cable relative to each To satisfy the latter problem, cables are manufactured with cores twisted together to form pairs, and adjacent pairs may be twisted at different rates. A circuit should always utilise the two conductors of a pair for out and return. Common returns should not be used in such cables. The effect of twisting the conductors together in such a fashion is that cancellation of any induced voltage occurs across any load terminated at the ends: of the cable pair.  Often cables are made up in multiples of quads instead of pairs. In such cases a pair is formed by utilising the diametrically opposite cores. The resultant cable is smaller in diameter than the equivalent multi-pair cable, since there is less wasted space within the cable. With the use of very high frequencies on carrier circuits and for broad bandwidth applications such as closed-circuit television, the problems of crosstalk and attenuation increase with frequency. Eventually, twisted pair cables become unsatisfactory. Coaxial cable, effectively a cable pair consisting of a central conductor surrounded by and insulated from an outer metallic sheath, is employed. The fields created by the high frequency signals are contained in the cylindrical space between the inner and outer conductors, thus alleviating the crosstalk problem. A larger spacing between conductors also reduces the high frequency attenuation. 4. POWER CABLES For both signalling and telecommunications applications it is necessary to distribute power to the lineside. For most purposes this is best distributed as a.c. and transformed and/or rectified locally to the equipment served. A wide range of power cables is manufactured to supply the electrical industry, and these are generally employed within signalling and telecommunications systems. The sheath and/or insulation material may have to be modified to suit the specifications for signalling cable. As most power distribution is single phase, 2-core power cables are generally used. The conductors may be stranded copper or solid aluminium.   5. SELECTION OF CABLE TYPE   5.1 Lineside Signalling Circuits Signalling circuits will be taken to mean d.c. or mains frequency a.c. circuits between an interlocking and a lineside location (or between locations) to convey signalling information. They are normally laid in main cable routes and may be very numerous in areas of complex        signalling. Cables for signalling circuits normally utilise conductors with only one strand, as mechanical strength is not of major importance. Typical cross sectional area is 0.5 to 2.5mm 2. To economize on installation costs, a smaller number of cables with a higher number of cores is preferred. 5.2  Tail Cables   On-track cables (tail cables) to lineside equipment (e.g. signal heads, point machines etc.) from relay rooms or location cupboards must withstand physical damage and vibration. The B.R. standard cable has 50 strands to give it flexibility and a heavy-duty sheath for protection. The following sizes are commonly used: 5.3 Power Distribution   Standard industrial sizes of 2-core power cable are used. The size of the conductors will depend on the power loading and the consequent voltage drop along the line. For most types of signalling equipment, a voltage drop of 10% is usually the maximum acceptable. It is therefore important to perform an estimate of power consumption of all equipment before deciding upon the size of cable to install. Allowance should be made for possible future additions to the electrical load. Renewal of power cables at a later stage can be expensive. 5.4 Internal Relay Room/Location Wiring   Due to the diverse termination points of internal circuits, the only means of installing internal circuits is to use individual wires. Cables may be useful for wiring between racks or between different rooms/floors of a building to simplify installation by allowing factory pre- wiring. Alternatively, armoured (e.g. steel wire) cable could be used. This has fallen in popularity in recent years due to cost, difficulty of handling and difficulty in performing a satisfactory repair in the event of damage. 6 . METHODS OF TERMINATION   All cables and wires must be terminated to connect on to other equipment. Each individual conductor in the cable will normally be terminated, even though some cores may be spare. In addition to terminating the individual cores the cable sheath is often clamped to a fixed bar in the location or equipment room. This is to avoid the weight of the cable placing a strain on the individual terminations which could lead to breakage of the conductors. The following are the most widely used forms of termination: - 6.1  Crimped Termination   This method is mainly used for stranded cables. It is unsuitable for small cross-section single conductors as it weakens the conductor mechanically. It is  a  mechanical  method which involves compressing a metal termination on to the wire. Various types of crimped connector are available:- a) A "ring" type connector to fit over a screw terminal. This is secured by nuts and washers. b) "Spade" type connectors which can be inserted into equipment terminals without the need to completely remove nuts and washers. c) A special type of spade connector for use in BR930 relay bases. These are simply inserted into the relay base. The crimps are constructed so as to spring apart slightly and lock the wire in position. A special tool is required to extract this type of connector d) "Shoelace " type connectors which can be inserted into equipment terminals without the need to completely remove nuts and washers. There are terminals available capable of inserting wires without the need of ferrules. Its recommended to use ferrules for multi stranded wires, however single wire cores can be inserted without a ferrule. For all types of crimped connection, it is important to choose the correct size to suit the terminal, the size of conductor and the size of insulation. Its also important to ensure the terminal can withstand the current carrying capacity of the wire. 6.2  Screw Terminals   These are used in conjunction with crimped terminations or to directly terminate the conductors of solid cored cables. The cable is held tightly by a screw and/or nuts and washers to provide mechanical strength and electrical continuity. Where screw terminals are used, it is common to provide disconnection links to enable portions of the circuit to be isolated. 6.3  Plug Couplers   Where modular equipment requires to be unplugged it is common to connect all wiring to a plug coupler. Wires may be soldered or wire-wrapped for security. This allows very quick disconnection and reconnection and avoids the need to check and/or test the wiring when a module is replaced. Plug couplers are often electrically or mechanically coded to ensure that they are only connected to the correct equipment. 7. CABLE ROUTES   A safe route must be determined for the cables, both within buildings and externally. Within buildings, suitable ducts may be provided as part of the building or the equipment racking. If the cable route is shared with other than signalling cables, it must be ascertained that there is no hazard from electrical interference. Outside buildings there are several methods of cable installation used. These are described below. 7.1 Troughing   Troughing is laid on the surface. It is usually inset into the ground for stability and the safety of staff walking along the track. Cable installation is simple. The lids are removed, the cables placed in the trough and the lids replaced. Two types are now in common use:- a)  Ground Level Sectional Concrete Troughing. b) Ground Level Plastic Troughing. Plastic troughing is easier to handle but requires more accuracy in installation. Lids must be clipped on rather than being held in place by their own weight. 7.2  Ducts The following types of cable duct are in general use:- a) Earthenware duct  b) Thick wall Rigid V.C. duct c) Thin wall V.C. duct. This duct must be laid in concrete d) Asbestos Cement duct - not generally available but has been used in the past in large quantities. e) Steel duct f) Flexible plastic pipe - this is corrugated along its length to allow the pipe to bend  A common problem with all ducts is that over a long period of time they tend to accumulate debris which is either washed or blown into them. After a long period of time has elapsed, this may make further cable installation more difficult. 7.3 Cable Racks or Trays   Slotted steel or plastic trays may be fixed to lineside structures, retaining walls etc. Cables may be fixed to this using plastic cable ties. The cable route is easily accessible for installation purposes but is also exposed to the environment and may be unsatisfactory in areas where vandalism is a problem. A similar method is to use cable hangers - hooks on to which the cable is placed and held in position by its own weight. This method is particularly useful in tunnels where there is little risk of vandalism and clearances are limited. 7.4  Buried Cables   Provided the cable sheath is suitable cables may be buried direct in the ground. This avoids the cost of providing an expensive cable route. Cables are normally buried in one of two ways:- a) Laid in a trench with protective tapes or tiles and backfilled. b) Mole ploughed using a mechanical mole ploughing machine. In both cases warning markers should be provided on the surface at regular intervals. Buried cables suffer from several problems:- a) It is difficult to install further cables at a later stage without risk of damaging existing cables. b) Cables are vulnerable to excavations by others as they are not visible. Cable markers may eventually become obscured. c) Fault location and rectification is more difficult. d) Over a long period, ground movements and the growth of tree roots etc. may stretch and damage the cables. When specifying the type of cable installation, the engineer should take all costs, risks and benefits into account. 7.5   Aerial Cable Where an existing pole route is in good condition, it may be economic to install aerial cable. Aerial cable is however vulnerable to damage (gunshot, falling branches etc.) and the effects of lightning. Ordinary cable is unsuitable for aerial installation. Aerial cable has a steel strainer wire installed to provide the necessary tensile strength for hanging on poles. 7.6  Application   In general the application of the above methods are as follows:- 7.6.1 Track-side cable routes   Ground Level Concrete Troughing and Plastic Troughing is usually preferred where a large number of cables is required. Burying may be employed for small cable routes (i.e. single lines). Aerial cable could be considered if an existing pole route is still in good condition and the risk of damage or interference is low. 7.6.2 Under Track Crossings Practices vary but in general steel or asbestos cement ducts are preferable because of their ability to withstand vertical impact. In some cases thick wall P.V.C. duct has been used. Ducts should be installed sufficiently far below the track to be clear of track maintenance equipment (tamping machines, ballast cleaners etc.). 7.6.3 Platform Routes   In general, platform routes should be provided with cable ducts and associated manholes for access to joints and pulling through of cables. Usually, it is more convenient to use earthenware ducts for platform routes. Surface troughing or hangers along the platform edge may interfere with track maintenance. 7.6.4 Tunnels The method used will depend upon the construction and cross section of the tunnel. It is often difficult to install a ground level route which will be clear of track maintenance machinery. Cable trays or hangers on the tunnel wall are therefore the most suitable. It is of course possible to design new tunnels to accommodate a cable route. Whether this is best located on the tunnel wall or floor will be determined by the type of track and tunnel drainage requirements. 7.6.5 Tail Cables   Opinions vary on the best method. It is unlikely that there is a best method which suits both the signal engineer and the permanent way engineer. Cables may be simply laid across the top of the ballast. These are visible and easily removed and replaced. They are also vulnerable to damage by track maintenance and trailing objects on trains. Use of surface level ducts provides added protection but interferes with track maintenance. Placing the ducts below ballast level increases installation costs. Ducts can also become blocked with ballast and other debris. Surface cables secured to the top surface of the sleepers have greater protection than those laid loose across the ballast. This method may not always be acceptable to the track engineer. Tracks laid on concrete sleeper can use hard hats to cover the cable where hard hats are fastened on the concrete. 8.  CABLE CONSTRUCTION   A vast range of cables is now available. it is only possible to cover some of the main features of modem signaling cables in this section. There are many other cables widely in use for different application including control voltage to a Point Machine. Refer Figure 2 for the construction of a modern quad cable with Water Resistant property. Even though below section is based on Quad Cable Construction, we use this opportunity to discuss other alternative options available for armour, screen, internal & external sheath and the conductor insulation. Selection of PVC materials (XLPE -Cross Linked Polyethylene, LDPE -Low Density Polyethylene HDPE -High Density Polyethylene) and the addictive included for UV, Pest, Carbon /Iron /Copper/Mineral Dust, Acid /Salt, Industrial Cleaning solution    shall be selected according to the operators need and the type of environment for the intended application. It is signal engineers’ responsibility to ensure that cable will not fail and select the property in case operator doesn’t specify detailed requirement. 8.1 Conductor Materials   Copper is the most widely used conductor material due to its very low resistance and excellent mechanical properties. It is also available in sufficient quantities at an acceptable price. The copper is manufactured as wire of a consistent cross-section by repeatedly drawing the copper through holes in dies of reducing cross-section until the desired size is reached. As this process tends to harden the copper wire, it is usually annealed to restore its ductile properties. Annealed copper wires are complied to EN60811-203 /IEC 60228 .Refer RailFactor Article “Standard for Signalling cables “ as well for more details. Where rubber insulations are employed, the copper is generally coated with tin to prevent a chemical reaction between them causing corrosion of the copper and a change in the mechanical properties of the rubber. Where a large cross-section is required, aluminium may be used in place of copper (e.g. for power cables). Although Aluminium is more resistive, it is lighter and cheaper and has greater mechanical strength. Aluminium cables generally employ a solid conductor and are therefore more rigid than the copper equivalent. 8.2  Insulating Materials   Each core of a cable must be insulated from all others and must therefore be surrounded by an insulating material throughout its length. Signalling cables use thermoplastic (P.V.C. or Polyethylene) or elastomeric (natural rubber or polychloroprene (P.C.P.)) insulations. The addition of P.C.P. to rubber improves its resistance to weathering. In very wet conditions, however, it has a tendency to absorb water over a long period of time. This will adversely affect its electrical characteristics. With telecommunications cables, the capacitance between cores becomes significant with a.c. signals. Dry air is the best insulator but impractical for cable construction. In older cables paper was widely_ used. This effectively consisted of a mixture of organic fibres and a large proportion of air spaces. As paper insulation is no longer used, polyethylene ie: HDPE (High Density Polyethylene-Solid) insulation is common these days with Low Smoke, Zero halogen property especially in the tunneled application. 8.3  Formation of Conductors Quad formation of conductors are the most recent trend for multicore cables .They are constructed in 1 Quad (4 Core ) ,3Quad (12 Core) ,4 Quad ( 16 Core ) , 5Quad (20Core ), 7Quad( 28Core) and 10Quad ( 40 core) .Each quad is arranged in the form of a Star (Diamond)  and twisted together to get the best electrical property in terms of mutual Capacitance ( <45nF/Km) and Electromagnetic Compatibility compared to other formation which makes higher mutual capacitance .Lightly twisted pair formation is also available  for better Electro Magnetic Compatibility. German DB(DB416.0115-Standard) defined Quad cable is popular for CBTC /ETCS application. Quads are helically stranded in concentric layers and cables more than 7Quad include two extra conductors with perforated insulation for surveillance. Signal Engineer shall select the compatible cable with respect to their signalling solution. 8.4   Core Identification Cores are identified in a number of ways, for a DB defined Quad Cable as shown in Figure 2 on light brown  conductors black bracelets are printed in different combination .Eg: Two black circles printed  together and repeated on  fixed length apart ,One circle  printed and repeated on certain length etc . As a Designer I am not a big fan of such identification as its confusing for the technicians for the first time. Methods of identification can be classified into 5. a)       Coloured Tape wrapped around each core b)       Coloured Insulation (Especially for Signalling Application Power Cables) c)       Numbered Tape d)       Numbering Printed on the insulation. e)       Identification concentric rings (as mentioned above  on DB defined Quad Cable) When numbering is used care must be taken to avoid confusion between 6 and 9. The easiest method is to write the number (six or nine) as well as or instead of the numerals. Various systems of colour coding are used depending on the size, type and manufacturer of the cable. In a paired cable only one conductor may be colour coded. The numbering of cable cores/pairs always starts from one at the centre and increases towards the outside of the cable. Each end of the cable is identified - the A end is the end at which the numbering of each layer runs in a clockwise direction, the opposite end is the B (or Z) end. 8.5  Core Wrapping, Screen, Inner Jacket, Swellable Tapes & Armour Plastic tapes are overlapped around cores which collectively hold all the cores together, on top of it, a copolymer coated aluminium tapes are wrapped. Tinned copper wire of 0.5 mm. run along the cable making in contact with the aluminium tape. This arrangement provides the functional earthing (EMC) option for the cable. This continuity wire needs to be earthed along with the armour for earthing the induced current generated due to parallelism (double sided for AC Traction line and singe sided for DC Traction). This arrangement is protected with Black coloured Zero Halogen Low Smoke compound PVC Inner jacket. Steel Tape armour is   taped around the inner jacket. Swellable water blocking tapes are wrapped around the Inner jacket and Steel armour to avoid longitudinal water penetration. This arrangement along with inner and outer sheath is making the cable compliant to moisture barrier requirement per BS-EN 50288-1, EN 50288-7 or equivalent, water immersion test complying to IEC 61156-1. This construction is ensured to pass the Transversal water tightness and armour long water tightness test according to EN50289-4-2/A and water absorption for conductor insulation and outer jacket according to EN60811-402. 8.5.1 Types of Armour Armour provides additional mechanical heavy-duty protection, such as crushing, and resistance from pest such as rodent penetrating into inner conductor. Some cables will have nylon wrapping beneath outer sheath to protect from Termites and steel tape armour for rodent protection. Metallic armour not only provide mechanical protection it can also offer EMC protection but dose not replace the need for screen but lines  less than 25kV can consider avoid screen under specific conditions.   1) Steel Tape Armour Steel Tape armour is sandwiched between water blocking tapes for DB cable. These are used for buried cables. According to American Railway Engineering and Maintenance of way Association (AREMA) states that tape armouring provide high degree of shielding protection than shield wires. 2) Steel Wire Armour Steel wire surround lead sheath for some cable design and are used for buried cable. This will surround the braided sheath and such sheath are used for high frequency emc protection 3) Corrugated armour Corrugated steel /copper surround the cable lengthwise beneath the outer sheath which is used for lines less than 25kv  .This is mainly used in Optical Fiber Cable for optimum flexibility and recommended to replace with Fibers Reinforced Plastic (FRP) for electrified territory more than 25kV due to chance for high induced voltage.                8.5.2 Types of Shield/Screens Screening /shielding is used for reducing the effect of electromagnetic interference (EMI) or electrical noise which can disrupt the transmission performance in some environments. This noise may be because of external interference from other electrical equipment or because of interference generated within the cable from adjacent pairs (cross talk).   1)  Aluminium /polyester tape with a tinned copper drain wire          DB 416.0115-Standard Quad Cable referenced in Figure 2 have aluminium foil with attached tin plated copper wire .   2)  Copper /polyester tape with a tinned copper drain wire   This solution can provide better screening effect compared to aluminium foil. 3) Bare copper braid This is good for electromagnetic interference when the cable is subject to movements   4) Tinned copper braid Good for  electromagnetic interference in presence of corrosive atmosphere or high temperature 8.6  Outer Jacket  In addition to insulating individual cores, the entire cable must be contained within a sheath for both mechanical strength and environmental protection. Cross Linked Polyethylene (High Density Polyethylene Otherwise known as HDPE) are the most widely used. Low Density Polyethylene-LDPE) are also used depends on area of usage. Some older cables used lead, but its expense and associated health risks have led to its disuse. The choice of sheath material should consider the environment in which the cable will be used. Factors such as moisture, exposure to light and heat, the presence of oils and solvents, presence of carbon/iron dust, Train washing plant solutions, temperature, water immersion (IPX7) /submersion (IPX8) and the required level of resistance. In nutshell outer jacket is one of the most important elements for mechanical protection from external damages such as chemical (oxidation acid, oil), Mechanical (Abrasion), Environmental (Heat, Sun exposure, moisture, water), Fire exposure etc. Thermoplastic or Thermoset polymers are widely used where Thermoset have excellent properties against threats.               8.6.1  Ingress Level- Mechanical Properties.   Mechanical shock severity shall be shared with the cable supplier whether its Low (Energy shock of 0.2 J, mainly for household installation hence not applicable) or Medium (Energy shock of 2J-standard industrial application) or high severity (Energy shock -5J) 8.6.2   Ingress Level- UV Resistance.                Designer shall share the UV intensity requirement to the cable supplier based on the regional severity and exposure levels whether its Low (AN1 – Intensity ≤500 W/m²) or Medium (<500 W/m² intensity ≤700 W/m²) or High (<700 W/m² intensity ≤1120 W/m²). Refer Rail Factor Article “Standards for Signalling Cables” for more details.  8.6.3   Ingress Level- Water 8.6.3.1    Water Environment 8.6.3.2  Water Penetration The factor defines the water penetration in cables and to prevent the entry and migration of moisture or water throughout the cable. Water ingress can happen through Radial due to sheath damage and in this case, water enters in the cable by permeation through protective layers or due to any mechanical damage. Once water enter the cable, it travels longitudinally through out of the cables core. Where as longitudinal penetration moisture or water enters inside cables core due to ineffective capping or poor cable joint /termination .Please note water proofing and water absorption tests are different .There are no specific test for longitudinal water penetration for power cables .Radial water penetration test shall only be applied .Separate water penetration barrier are applied below the armour (or metallic screen layer )  and along conductor .Refer cable construction above in Figure 2     8.6.3.3  Moisture Protection Resistance offered by the jacket and the additional chemical used are ensuring the protection. However, the material with highest degree of water resistance is often not flame resistant, hence a tradeoff must be made between these two contradictory requirements. Choice of sheath material, make use of chemical moisture barrier and water blocking tapes can protect the cables from moisture.          8.6.4  Flame & Fire   8.6.4.1   Low Smoke Zero Halogen (LSOH) This is the property of cable to emit very low smoke and zero halogen and ensuring low corrosivity and Toxicity. Even though normal PVC cable ensure better mechanical and electrical properties, its poor in fire retardancy, corrosivity and low smoke capability.   8.6.4.2   Smoke Density Smoke can prevent fire fighters’ visibility and evacuation, especially in tunnel, work areas, control room and public areas. 8.6.4.3    Flame Retardant Flame Retardant property is vital, during a fire flame spread shall be retarded to limit to a confined area thus eliminating fire propagation. 8.6.4.4    Fire Retardant Property which when ignited do not produce flammable volatile products in required amount to give rise to a secondary outbreak of fire. 8.6.4.5    Fire Resistant Fire resistant cables are designed to maintain circuit integrity of emergency services during fire. Please note that Fire resistant cables are super expensive and normally considered for very vital cables (Eg; Fire cabinet ,depend  on contractual requirement .Please note that Fire Resistant and fire retardant are different property and fire resistant is more stringent requirement. The individual conductors are wrapped with a layer of fire resisting mica/glass tape which prevents phase to phase and phase to earth contact even after the insulation has been burnt away. The fire-resistant cables exhibit same performance even under fire with water spray or mechanical shock situation.               8.6.5    Pest Resistant                Depends on the intended area of the project ,there could be various threats  such as  ants, termite ,rodents , squirrels ,wood peckers ,other birds ,beetle and larva where cable contact with any plants to mention some .Various chemical compounds added on to the sheath ,depends on pest chemical and armours are protecting the cable .It may not be practical to have armoured cable for indoor application due to flexibility issue and outdoor environment have more threats . 9.   ELECTRICAL PROPERTIES SIGNALLING CABLES 9.1  Voltage Rating of Cable Signalling control cables are normally rated for 600v/1000V. Voltage range classification for LV, HV, AC & DC according to IEC 60038 are as shown in Table 3 Maximum for High Voltage for IEEE is 35kV and in some countries its 45kV, which is country specific. Refer Table 4 for maximum permitted voltage Vs Rated voltage.  9 .2   Resistance of Cable This is the resistance of wire which increases with distance and normally included in the cable data sheet from the supplier. Its measured Ω/kM @ 50Hz (or 60Hz) and 20°C. This is the main parameter to calculate the voltage drop of cable. Voltage received at the end gear shall not be less than 10% of the source voltage. This means when you feed 130V from the SER, signal at the track side should at least get 117V. Cable conductor size shall be selected based on voltage drop calculation and shall cross check with field gear data sheet that the 10% voltage drop allowed will still fall in the minimum required voltage Important Note: Signal Engineer shall ensure that the resistance value (Ω/kM) provided by the supplier in the data sheet is loop resistance or wire resistance. Loop resistance means it’s the value for two conductors. While calculating voltage drop, number of loops used for the respective circuit and its distance shall be used. 9.3   Reactance of Cable This is defined in Ω/kM @50Hz (or 60Hz). This is important parameter for MV cables which need to be asked from the supplier but for LV, designer can define the allowed limit for LV 9.4  Capacitance of Cable Measured in µF /KM which is mandatory parameter for MV cable and shall be requested from supplier. As mentioned above Quad formation have less than 40µF /KM. Lower the capacitance better the cable property. 9.5    Maximum Short Circuit Current (Conductor and Screen)   Maxum short circuit current in kA for conductor and screens for 1.0 seconds and 0.5 seconds respectively shall be requested and obtained from supplier. 10 CABLE TESTING It is not the purpose of this article to give detailed instructions on the procedures for testing and maintenance of different types of cable. However, the general principles of cable testing are described here. In general, whenever a cable is installed, repaired, re-terminated or jointed and at regular intervals during the life of the cable, tests must be made to ensure that: - a)  Each core is continuous and of the correct resistance. A rise in the resistance of a core could indicate a potential fault. b) Each core is insulated from all other cores. It is normal for the insulation resistance to fall slightly during the life of a cable. Serious deterioration must, however, be detected before it causes any safety hazard. c) Each core must be adequately insulated from earth. Unwanted connections to earth are a potential danger to all signalling circuits and must be avoided. Where the cable has a metallic sheath, the insulation tests must include the sheath. Where the sheath is earthed and/or bonded for reasons of safety or noise immunity, the continuity of the sheath is also important. The continuity tests may be made using a suitable digital or analogue multi-meter set up to measure resistance. All tests will require the cooperation of persons at each end of the cable. A telephone circuit between the ends (using the cable to be tested if convenient) is essential to carry out an efficient test. The simplest method is to put a loop between one conductor and each other conductor in turn at one end of the cable. The loop resistance is measured at the other end using the meter. Any variation between individual readings (and changes since the previous test) should be investigated and resolved before the cable enters (or re-enters) service. Insulation and earth tests should use a suitably rated insulation tester (1000-volt Megger or similar for signalling cables). Tests should be performed between each core and each other core in turn. The acceptable value of resistance for a cable will depend on the circuits connected through it. However, as a general guide, a new signalling cable should give readings better than 10MΩ (when terminated). Readings less than 1MΩ could potentially be dangerous and require urgent investigation. The earth test may initially be carried out between earth and all cores connected in parallel. Only if this test is unsatisfactory need individual cores be tested to earth. Although a new cable is always completely tested before being brought into use, a complete test of a working cable is not always practical without serious disruption. In this case, routine tests are often carried out on a sample of cable cores (spare cores if available). Previous readings should be retained for comparison. 11.  DATA CABLES Ethernet cables falls under this category. They are classified into different category Cat 1 to Cat 9, whereas Cat 1-4 are not suitable for modern day rail application and above Cat7 is not yet came into application while preparing the article. Refer Table 4 for category classification. Data cables with twisted pairs have different construction depends on the purpose, cable shall be selected. Refer Table 6 for various construction. 12. Fiber Cables Although many signalling applications must use metallic cables, the availability and cost of fiber optic cables is rapidly improving. Instead of electrical signals, they transmit information by passing light signals along the length of a glass fiber. Internal reflection contains the light signal within the fiber. Although not specifically employed in conventional signalling systems, fiber optic technology has the following advantages and necessary for modern communication-based train control system: - a)  An extremely high capacity and bandwidth. b) Immunity from all types of electrical It is therefore of great use for communications purposes on electrified lines. Conventional jointing techniques are not applicable to glass fiber cables. Instead, the two ends must be cut squarely, butted up to each other and fused together by the application of heat. This is a very precise operation as any irregularities in the fiber will cause attenuation of the signal. Much of the work of jointing fiber cables can now be done automatically by sophisticated (and usually very expensive) fusion splicers. The action of cutting the two ends squarely, aligning them for a parallel joint and fusing for the correct period of time is largely automatic. Even with the high degree of automation, fusion splicing is not always 100% satisfactory each time. It is therefore usual to provide additional spare fiber at the joint. This must be accommodated within the joint closure. Category cables have limitation to transfer data more than 100meter, Fiber has significance in this case. There are two types of fibers: Single Mode: Long Distance Application Multi-Mode: Short Distance Application Single mode Fiber must be complied to G652-D type as per ITU-T standard and multimode with IEC 60793-2-10  There are two types of construction Loose Tubes used in cable concrete trough, direct buried and other harsh environment Micro Tubes for less harsh environment The END  NOTE :- Please comment if you wish to include Cable Voltage Drop Calculation , Stanadard conductor sizes and a sample cable plan 

Read Full Article

Deepu Dharmarajan -
Posted 132 days Ago

CH12B | Standards for Signalling Cables

Signalling

Railway Signalling, Communication and Power distribution for signalling equipment falls under Signalling Cables  category. Signalling Cables are categorized as high voltage, low voltage ,extra low voltage and fibre cables. According to IEEE ,high voltage cables are cables handling voltages greater than 1kV up to 35kV for AC Vrms and 1.5kV to 50kV for DC respectively .There are difference in this range from country to country  and can go up to 50kVrms . Low voltage cables carry voltage between 50V to 1kV for AC Vrms and 120V to 1.5kV for DC and extra low voltage cables carry voltages less than 50v  for AC Vrms  and 120V  for DC . Note!: Standards and requirements vary from country to country and user of this article shall check with the operator for the standards with in the country of application. Below table list the standards used in major railway countries and alternate standards may be proposed where no standard exist for certain requirement.                                 List of Standards and Application  Below are a list of  requirements , standards  along with title for various cable requirements .Requirements are classified as Mechanical and Electrical . 1.1. Mechanical Properties  Requirements for the protection of the cables against potential threats  1.1.1. Water Protection Stringent water protection requirements are applied based on the intendent environment and cables properties are defined from negligible water threat to immersion or complete submersion. Water penetration can be Radial due to sheath damage and water travels longitudinally. Water blocking tapes are considered as  moisture protection.Below are various standards which are applied depend on intended application.                         1.1.2. LS0H (Low Smoke, Zero Halogen) Especially tunnel and enclosed environment its important to ensure cable properties are free from emitting hazardous gas and smoke during fire.                                         1.1.3. Fire& Flame  Retardant ,Fire& Flame  Resistant Please note that retardant and resistant have different meaning ,Fire /Flame resistant is more stringent and cable will be expensive .Fire/Flame retardant cables resist the spread of fire into a new area, whereas fire-resistive cables maintain circuit integrity and continue to work for a specific time under defined conditions. Resistant in this context is defined as a material that is inherently resistant to catching fire (self-extinguishing) and does not melt or drip when exposed directly to extreme heat. Retardant is defined as a material that has been chemically treated to self-extinguish.                                                           1.1.4. Ultra Violet Protection Cable which are directly exposed to sunlight shall be resistant to  Ultra Violet  radiation. Test shall be conducted as per requirement on the intended terrain of cable application  for Low(AN1) ,Medium(An2) or High(AN3)                  1.1.5 Abrasion & Crush  Abrasion and crush load resistance test to be performed to ensure the cable can have longer life span for the signalling system life.           1.1.6 Longer Service Life Crush  Thermal aging tests are performed as defined in EN 60811-401 to ensure cables can long last at least life span of the signalling system               1.2. Electrical Properties  Below list cover some of the standards for electrical properties of the cable    1.2.1. Ohmical Resistance              1.2.2. Mutual Capacitance                1.2.3. Insulation Resistance               1.2.4. Di-Electric Strength               1.2.5. Conductor       1.3. Australian Standards

Read Full Article

Deepu Dharmarajan -
Posted 458 days Ago

CH13 | POINT CONTROL AND OPERATION

Signalling

Coming Soon...

Read Full Article

Deepu Dharmarajan -
Posted 184 days Ago

CH14 | Power Supplies

Signalling

SIGNALLING BOOK | CHAPTER 14 1. Introduction As Signalling system and its elements  seeks 100% availability in almost all units and subsystems. Seamless power supplies are required for all electrical products to drive and achieve highest level of availability .It is possible to achieve various levels of redundancy based on end operators requirement and capacity to invest to make it 100% available at all time ! We can categorize Signalling power supply into centralized and distributed .Centralized are the one which Signalling Equipment Room  has its own feeders with alternate sources of upstream supply with UPS back up (Number of Hours for  back up needed are decided by the operator) and feeding into wayside location cases along the line  ,where as distributed option has individual Main and alternate feeders available at each location cases /huts along the line with relevant UPS back up. Both has its own pros and cons .For a centralized power supply ,it requires higher capacity feeders and bigger dia conductors to reticulate into trackside location cases. Alternatively can step up the source at SER and step down at location cases to reduce cable cost.Where as distributed system requires main source feeder and alternate  feeder at each location .Selection shall be based on budget and trade off between pros & cons for both system. 2. Steps to design the power supply There are many practices which could be implemented .Below steps are the one I apply for designing a power supply system if something specific is not asked for .It depends on individual designers /employers/operators practice Familiarize end operators requirements from contract or detailed specification. Understand country based standards required to be applied for the system. Gather power supply requirements of each drives. Assess the supply requirement for grouping based on voltages. Identify Static and Dynamic Load. Prepare the load requirement excel with possible grouping. Calculate Reactive Power for Transformers Calculate feed Circuit Breaker rating ,wire sizing Detail Design of  the sub system . Procurement and Manufacturing of one Power Distribution Cabinet (PDC) Type approval to comply EMC requirements ,IP requirements and other needs to be approved for the railways. Mass production of power distribution cabinets   Factory Acceptance Test. Installation of the System Power On and Integrated Test . 2.1 Familiarize end operators requirements from contract or detailed specification Contract or Technical Specification or System Requirement Specification define the requirements to be followed for  the power supply design .It could include the local rules ,standards and practices to be applied ,redundancy requirements (Eg:-N+1 ,N+ N ) ,Spare Capacity Requirement ,Rated load for transformer (Eg: Transformer shall not be loaded not more than 75 % of rated load ),local and remote monitoring features ,UPS back up  requirements ,Battery Types ,Hours of back up needed ,pre-emptive warning of components needed (advance warning for the product before its going to be faulty ) ,Insulation Monitoring Requirements ,Earth Leakage Protection Requirements ,Lightning Protection ,Type Test (For EMC /IP) ,How system shall behave when earth leakage happens (Eg:IT Earth Systems per IEC 60364-Clause 4.3.3.1),require to warn for maintainer to rectify the fault at secondary side of a transformer ) ,detailed calculation and other requirements (Eg:- detailed calculation for each feeder ,each fuse/wire size ,calculation for identification of maximum short circuit current ,Voltage drop ,maximum load to validate the wire are considered for protector and wire/cable selection.) 2.2 Understand country based standards required to be applied for the system Each country have either its own standard or follow reputed standards ,which shall be applied while designing a signaling power system .Again this is based on technical spec ,some time some requirement may be over ruled in technical specification.As an Example ,Australia seeks MEN (Multiple Earth Neutral) ,where as Signalling system require IT earthing system per IEC 60364.Direction shall be sought from customer unless otherwise specified.Country standard/practice includes earthing systems requirements ,wire colour coding ,EHS requirements (RCD fitted MCB) and code of practices. 2.3 Gather power supply requirements of each drives. Designer shall gather the approved system architecture with power needs ,product data sheets (Detailing reactive Power /Active Power ,Frequency /Voltage Tolerances,start up current ),any tools for validation of the calculation comes under this step. 2.4 Assess the supply requirement for grouping. In this step ,we identify the possibility of power grouping .Systems which require two separate sources of supply (Two UPS supply or Two Main Supply or One UPS and One Main Supply) ,subsystem which require one source ,but from a fail proof Auto Transfer Switch (ATSw),Types of Voltages (AC/DC with rating) ,Reticulated Supply to other destinations are the factors to be considered. Note :While preparing a load calculation excel ,these grouping will prove useful   2.5 Identify Static and Dynamic Load. As you know some of the loads to the power system are permanent (static) ,where as some loads are required while the drive operates(dynamic) .As an example ,Point Machine draws current when system calls the machine to operate ,similarly only one signal operate out of a two or three aspect signal at any time, and all relay don't operate at same time to mention some examples (Some relays are normally up but some are picked as per control logic .Designer shall identify these factors to save cost and to avoid over designing .  There could be numerous point machines in the layout which don't operate at same time .Designer shall either identify himself /Herself or get identified from Interlocking expert how many points can be operated at same time to decide the total load for the system .Its waste of money to provide feeder capacity for 60 point machines when maximum 20 can be operated at any time ) .Designer shall also identify any point sequencing are considered  in the route table  .This means if there are 10 point machines to be called for a particular route setting and if all are lying in unfavorable position from previous train move or have self normalizing feature in the interlocking and route requires opposite move  ,interlocking can call five of them first and next five with a time delay .This will be defined in signaling interlocking control table Another factor is electro mechanical components .High current is only required in few seconds at start up to gain  initial torque for a point motor and reduce gradually which will be defined in the product manual.This factor shall also be considered .I like to consider starting current as worst case instead of operating current when other factors are optimized to the maximum. 2.6 Prepare the load requirement excel with grouping. Now its time to record all these in an excel sheet as per the grouping ,some employers /operators might have predefined tools ,if so please use the validated tool. Creating new tool /programmed excel require authentic review ,verification to make it error free.This table can group as per the reactive power(Apparent Power) or Active Power to identify the rating of feeder and transformers. If the data sheet provide active power ,designer can consider to convert to reactive power based on power factor of the product .Electronic products have close to unity power factor theoretically ,where as heating elements might have power factor of 0.8 or less .This tool contains all the different voltage requirements with its group to arrive at total load to the Power System . 2.7 Calculate MCCB Circuit Breaker rating ,Wire and Cable sizing(Downstream -Power Distribution Cabinet) Excel spread sheet is prepared with load requirement for each group ,including AC voltages and DC voltages (with converters) . Adding all the load will give the total power for the power supply system . As an Example :- If Point Machine and Signals requires 110V AC ,which can be clubbed into one group or as separate group to feed from separate isolation transformers with Automatic Transfer Switch.Interlocking cabinet ,AutoMatic Train Super Vision /Control Cabinet ,Communication Cabinet ,Secondary Train Detection Cabinet (Track Circuit /Axle Counter ) might need 230V with two independent supply (One from UPS supply Source and One from Rail Supply Source ) to feed the Redundant hardware of the respective cabinets .Similar feeder requirement can be clubbed together as per operator practice .In order to read the dry contact (for Point Machine Detection,other field status ) into I/O card file or to Pick a relay we might need 24V DC or 48V DC .All DC requirement of same voltage can be grouped together .These DC voltages are generated with the help of AC/DC converters (N+1  OR  N+N *arrangement as per end operator requirement) which requires a fail proof 230V AC source which we might use a static Auto Transfer Switch (ATSw) Note* : Assume Total DC load requirement is 500 Watts ,If one of the AC/DC converter capacity is 500 Watts .One number of AC/DC converter is required (ie . we need 1 No of AC/DC converter rated for 500Watts to feed the load  which is considered as ‘N’ unit  ) .To make an N+N arrangement we use 2 nos of AC/DC converter and the output is paralleled to same bus bar .There by if one converter(N) is failed other will be continuously feeding the bus bar .There by making 100% redundancy .By using independent ATSw ,to feed both N will make the availability even better. Sample Calculation : we get total reactive power requirement from the excel table =60KVA (while adding all the total static and dynamic load for one single feed at any instance of the operation) and end operator specification requires an additional 20% capacity with feeders to be fully wired for future expansion and downstream isolation transformers shall not be loaded not more than 75% rated load . So the total load requirement = Actual Load X 20% Spare Capacity /75% rated load =60KVA x 1.2 /0.75 =96 KVA In order to achieve 100% redundancy we need two independent MCCB and Transformer with 96KVA load for the Power Distribution System .Both sources can be UPS or One UPS and One Normal Supply .There by achieving redundancy from single point failure(Refer the figure) .Both these sources are fed into two independent MCCB which is feeding 100KVA transformer (Next higher size of total load 96KVA) .Let the downstream cabinet transformer be 3 phase 4 Wire transformer and we can segregate and balance the load on each phases at secondary of the transformer for each group (230VAC , 230V/110VAC ,48/24V DC (AC/DC converter with input supply 230V AC ) making use of different phases by balancing the load on 1 :1 Isolation Transformer (400V ,3 Phase ,4 Wire Transformer) 2.8 Downstream Power Distribution Cabinet MCCB Rating Calculation Total Load is =96KVA (100KVA Transformer) Total Current on each MCCB =Reactive Power /1.73 (Root 3 ) x Voltage =96 /1.73 x 400V =138.72 Amps We shall consider the inrush current of the transformer ,which is 1.5 times of total current (worst case) So total current will be =138.72 x 1.5 =208 Amps We can select the next higher available rating for MCCB =250 Amps This means we need two sources to feed these two MCCB in the Power Distribution Cabinet(Downstream Incomer) Cable and wire size shall be selected based on this load or voltage drop from feeder or Short Circuit Current which ever is the highest . Upstream UPS and Battery to feed these sources shall be designed for Online operation .Battery banks are designed based on the back up hours needed as per end operator requirement (say 8 hours or 24 hours or 48 Hours ).As UPS design itself is a long topic will include UPS design in another article . 2.9 Detail Design the sub system . We have selected the downstream transformer ,MCCB rating which are fed from Two UPS or 1 UPS and 1 Non UPS Main source Supply . Upstream sources (UPS or Normal ) shall be connected to MCCB which is fed to Primary of Transformer .Out put of the Transformer is fed into a 3 phase bus bar (4 wire ) .Power shall be distributed from this bus bar into each drives /cabinet protected with MCB's From the excel spread sheet, for each group MCB has to be designed as per Reactive Power value . Say for Example if Cabinet 1 require two sources of supply and each load is 1000VA .MCB rating is calculated as below MCB 1 =1000/230=4.34 Amps and the next available size is 6Amps selected for MCB 1 .Redundant supply also have same 6Amps protection(MCB 2) As per the grouping in the excel ,other distribution to be made to feed all the drives and cabinets. A sample single line diagram(Figure 1)  is shown below for better understanding Detailed drawings to be produced further from block diagram /Single Line diagram for each feed with correct MCB rating and wire sizes. This  shall be selected based on the current carrying capacity. Figure 1.  Sample Single Line Diagram 2.10 Procurement and Manufacturing. Equipemnts and components shall be procured as per the designed parameters and built into cabinets (earth metallic enclosures) with correct IP requirement defined by the end operator .An IP 42 cabinet shall have a roof with fan .Filters to be designed and installed ,if EMC test is failed as per relevant standards requirements (EMC standards and requirements will be covered in another topic) and further tested to clear EMC test 2.11 Factory Acceptance Test. A detailed procedure to be prepared to perform factory acceptance test ,to test Insulation monitoring , Earth Leakage ,No load test ,Full load test to cover all the functionality and the readings shall be recorded in the corresponding recording templates and duly signed by relevant parties. 2.12 Installation of the System Factory tested cabinet shall be transported to project site for installation and completion of UPS and other sub system integration wiring. 2.13 Power On and Integrated Test A professional Engineer shall witness the power on after his inspection and Testing and commisioning team will further perform the integration test to all end drives 3. Earthing Systems Functional Earthing and Protective earthing(PE) are  carried out at the electrical installations .A functional earth connection serve the purpose other than electrical safety and might carry electrical current as part of normal operation .For the functional earthing cases a special terminal is provided for the installer to connect external earth usually for the purpose of noise reduction .Screen earthing of a cable is a  functional earth . A protective earth is used to protect the operator by means of reliable ground connection to make sure the touch current wont exceed certain values .In nutshell Protective earth is intended to protect personals from electric shock during an earth fault .This earthing is performed for  any metallic exposed part to the Main earth terminal in the Signalling Room. Fault current will flow through this conductor to earth which in turn on to the protective devices such as RCD (Eg residual Current Device Fitted MCB) to safely open the circuit within 0.4 seconds,where as functional earth is used to reduce radio frequency noise .Functional Earthing and Protective Earthing must be connected to separate earthing system and can be tied together through Potential Equalisation Clamp.(PEC) . Example :- Cabinet case earthing is a type of Protection Earthing ,Shield /screen earthing of a cable is a type of functional earthing in a signalling installations. 4. Type of Protective Earthing System. There are few types of earthing system (Protective Earthing ) implemented as per country practices. These can be broadly classified as TNS Earthing System ,TNC Earthing System ,TNC-S Earthing System ,TT Earthing System and IT Earthing System. This can be applied on to the primary side of the isolation transformer  of a downstream Power Distribution cabinet. The supply directly feeding the signalling equipment shall be isolated from earth(floating) as per IEC 60364 IT system (e.g. 600 V a.c and 110 V a.c supply). Refer to Clause 4.3.3.1.All the supply fed to the signalling element will have floating neutral (IT earthing system ) with neutral cut through Insulation Monitoring Devise or Earth Leakage Device . The ELD/IMD  device shall be used for first fault condition monitoring only – the ELD device shall not be used to trip circuit protection during either a first or second fault condition.  The first fault in the IT systems should be identified and fixed immediately to avoid a second fault from occurring.Refer Figure 1  to identify IMD connected to the secondary side of the Isolation Transformers  and Earth Leakage Relay connected at the Primary side of the transformer in which the relay contact is used to trip the MCB  and there by  isolating the group .This is to avoid nuisance tripping of upstream supply when earth fault occurs in a power group in the downstream. T(Terre or earth)  Denotes that the Power Distribution System at SER is solidly earthed independently of the source earthing method. N(Neutral)  Denotes that a low impedence conductor is taken from earth connection at the source and directly routed to the Power Distribution System at SER (Signalling Equipment Room Signalling Power Supply) for the specific purpose of earthing of the PDC system S   (Separate)  Denotes that the neutral conductor routed from the source is separate from the protective earthing conductor ,which is also routed from the source (Upstream council/Rail supply ) C(Common )  Denotes that the neutral conductor and the protective earthing conductor are one and the same conductor used 4.1 TNS (Terre ,Neutral, Separate ) Earthing System. Here Terre stands for Earth .In this type of earthing system neutral conductor routed from the source is separate from protective earthing conductor ,which is also routed from the source .Upstream supply normally tapped from Council (Government Electricity Authority ) or Railway exclusive supply which is the source for power distribution system .This is used as supply source in the Power Distribution Cabinet or UPS depends on the power supply distribution requirement at the downstream on a signalling power distribution cabinet .For a three phase source ,will have five wires (Phase 1 ,Phase 2 ,Phase 3 , Neutral and Exclusive earth ) and a single phase source have three wires (Phase ,Neutral and Earth ) leading into your Signalling Power Distribution Cabinet or UPS .Here Neutral and Earth are separate conductors and earthed at source.No separate dedicated earth used at Power Distribution Cabinet End in the Signalling Equipment Room. Refer Figure 2  for TNS earthing system details Figure 2 TNS Earthing System 4.2 TNC (Terre Neutral Common ) Earthing System . Here C denotes that the neutral conductor and the protective earthing conductor are ONE and same conductor is used .For a three phase source will have four wires (Phase 1 ,Phase 2 ,Phase 3 ,Combined Neutral and Earth ) and two wires for a single phase system (Phase and combined Neutral and Earth) In this type of system joined Neutral and Earth are earthed at source(upstream) end and destination end (downstream ) on separate earth electrodes.There could be additional electrodes at source end as shown in the Figure 3 Figure 3 TNC  Earthing System 4.3 TNC-S System This earthing system is an enhanced version of TNC system .In this type of system a three phase  source(Upstream)  will have four wires (Phase 1 ,Phase 2 ,Phase 3 ,Combined Neutral and Earth ) and two wires for a single phase system (Phase and combined Neutral and Earth) .That is,Joined Neutral and Earth at  source(Upstream)  end but separate Neutral and Earth conductor at downstream(PDC) end .In nutshell the difference for TNC-S from TNC system is that there are five wires used at downstream end(PDC ) joined into four wires towards source(Joined Neutal and Earth toward Source) for a three phase system and three wires (Phase ,Neutral and Earth ) joined earth and Neutral towards source and joined Neutral and Earth in a single phase system .Refer the Figure 4 below for TNCS-S earthing system details . Figure 4 TNC-S Earthing System 4.4 TT System In this type of earthing system ,there are four wires (Phase 1 ,Phase 2,Phase 3 and Neutral ) for a three phase system and two wires for a single phase system .Both source (Upstream ) and load (Downstream ) have exclusive earth and neutral is tied to earth at source end not at load end (downstream /PDC). Refer  Figure 5 below for TT Earthing System details Figure 5  TT Earthing System 4.5 IT Earthing System This is similar to TT earthing system .However neutral is floating compared to other types of earthing system .Neutral is not earthed at source (upstream ) or Load (Downstream ) .That is your Power Supply Cabinet . Both upstream and Downstream has exclusive earth ,however source earth is routed via Insulation Monitoring Device which can use for monitoring the insulation fault.Accepted earthing practice for  Railway control systems are as defined in IEC 60364 -4-41 .This means  the earthing system of the Low Voltage supply directly feeding the signalling equipment shall be IT earthed (Isolated from Earth)  through an Insulation Monitoring device or an earth leakage detector .An earth leakage in the secondary side of the transformer feeding the signalling gears shall not trip ,but it shall be warned to the operator when first leakage detected and maintainer to be send to identify the cause .This will not cut the feed to the system at same time at the primary side of the isolation transformer ,eearth leakge realys are implemented to prevent nuisance tripping to the upstream UPS or the alternate normal supply.Refer Fig 6 for TT earthing system Figure 6  IT Earthing System 5. Power Earth ,Signalling Earth ,and Communication Earth It is always advisable to have separate dedicated earthing system for Power supply subsystem ,Signalling System and Communication System . Communication and Signalling system exclusively requires functional earthing for EMC purposes where as Power Distribution System requires Protective earthing .Signalling Earthing System can be used to earth all the exposed metal part for the protective earthing of the signalling system and communication earthing system can be used for functional earthing and protective earthing of the communication cabinets respectively . All these earthing systems can be tied together with a potential equalization clamp which is an open circuit between earthing systems and which conducts when there is an earth fault . This practice is adopted in Sydney Practice 6. Earth Leakage Detection An earth Leakage System and Insulation Monitoring system shall be implemented in the signalling system at primary of the isolation transformer for the Power Distribution System and Secondary side of the isolation transformer .Earth Leakage Relay contact can be wired on to the trip coil arm of the transformer to isolate the downstream from source when leakage exceed a certain set value .This set value shall be based on the maximum leakage current possible from the end equipment and the current that can electrocute the person comes in contact .For an example .If leakage current from a signalling cabinet is 40mA and above this current can electrocute a person ,ELR shall be set for 40mA and if it exceed this value the incoming MCB will isolate the source by tripping the system . 7. Insulation Monitoring Device (IMD) This is another protective mechanism ,especially in IT earthing system which is used to monitor the leakage on the insulation of the conductor and can be locally and remotely monitored 8. Lightning Protection Its advisable to implement lightning protection for the conductors from the source for a distributed power system when conductors are exposed to lightning and thunder .There are protective devises available to connect across the conductors which are available in the market .It shall be implemented based on your operator practice 9. Local and Remote Monitoring Its also vital to read the status of various group of supply, incoming power availability ,UPS availability ,UPS on battery , Earth Leakage /Insulation Monitoring Status ,Current ,Voltage ,Frequency ,Synchronization ,ATSw status to be locally monitored (through local indication on the cabinet ) and remotely monitored (for maintainer to rush ) through Automatic Train Supervision system .Telemetry could be used to transmit these status remotely. 10. Summary This article cover the downstream power supply cabinet requirements and  its out of scope for Upstream Feeder and UPS design which is considered as Electrical scope .However will cover in another article for those who are keen on it    

Read Full Article

Deepu Dharmarajan -
Posted 452 days Ago

CH15 | ROUTE RELAY INTERLOCKING

Signalling

CONTENTS   Introduction Push Button Interlocking Point Circuits Route Locking Signal Aspect Controls Route Releasing Overlaps Preset Shunt Signals DISCLAIMER : THIS ARTICLE DOSEN'T REFLECT THE CURRENT NSW PRACTICE AND MORE OVER ROUTE RELAY INTERLOCKING IS GETTING REPLACED WITH COMPUTER BASED INTERLOCKING.THIS ARTICLE IS PURELY FOR INTERLOCKING STUDY PURPOSE  AND HELP TO GAIN KNOWLDEGE ON INTERLOCKING .CIRCUITS USED HERE SHALL NOT BE  USED FOR OPERATING LINES WITHOUT CHECKING   LATEST PRACTICE .THIS IS BASED ON AUTHORS UNDERSTANDING OF THE NSW INTERLOCKING  INTRODUCTION 1.1 Development of Relay Interlocking Systems The earliest interlockings were mechanical, between the levers of a frame but, with the development of block systems and track circuits, electrical controls were added. Staffing levels could be reduced by displacing a number of small signal boxes by fewer, larger installations. Fully electrical interlocking systems became necessary to control power operated signalling equipment. Initially, miniature lever frames were used. There are however many advantages in using a control panel incorporating buttons and switches into a diagrammatic representation of the track layout. With panel operation, a totally relay based system was required. Many suppliers produced their own different systems which, although different in detail, followed similar principles of design and operation. The signalman's control device was usually a button or a switch. Unlike the lever, it was free to move at any time. The relays now provided the security of the interlocking system. Additional indications had to be provided to show the signalman the state of the interlocking. During a period of substantial investment in signalling modernization in the 1970's, design, installation and testing resources were in short supply. British Railways  invited major suppliers to offer standardized interlocking systems which could as far as possible be factory wired and automatically tested. The contractors met the need with modular or "geographical" systems. The two main systems adopted, the Westinghouse "Westpac" and the AEI (GEC later acquired by Alstom) systems underwent several stages of development and were widely used. These systems certainly provided for very quick installation but there were disadvantages. The most important was that each development of a system was incompatible with its predecessors. The two systems were very different in their design philosophy. Westinghouse adopted a "one set per function" approach which led to high levels of redundancy, whilst GEC provided several sets combined as necessary for the function present. This approach increased substantially the quantity of inter-set wiring. Due to rising costs and problems of spares and modifications, geographical systems have fallen in popularity. State Railway Authority of NSW (later RailCorp, now TfNSW ) never adopted any form of geographical interlocking but has for some years purchased interlockings built to its own set of standard circuits. BR(British) also developed a set  of typical circuits for free-wired interlockings which  in operation  would appear similar to the geographical systems and adopt a high level of standardization of circuit design. These were incorporated into a BR Specification (BR850) which is probably one of the most standardized, and probably the last, relay interlocking specification in widespread use. On BR the use of route relay interlocking systems has now been superseded by solid state interlocking for all new work. As most route relay interlocking systems follow similar design principles and methods of operation, the State Railway Authority of NSW(Railcorp/Currently TfNSW) circuits will be used throughout for reference. NOTE:- This article is purely written for study purpose and shall not be applied without checking current practice  1.2 Relay Types   Various types of relay are used in the interlocking. As well as neutral relays, slow to operate, slow release and magnetically latched relays are used. It is important that the operation of each type is understood, and circuit symbols recognized, in order to follow the operation of the equipment. In particular, latched relays will remain in the last position they were moved to. 1.3 Diagrams   All the circuit diagrams used for reference are based on the NSW (New South Wales. Australia) standard circuits. 1.4 Variations   In practice, different installations may vary slightly in detail of circuit design. For example, full overlap swinging facilities may not always be provided. It is important to understand the relationship between the control tables and the interlocking circuits. The circuits must always be designed to function in the manner described by the control tables. 1.5 Relay Names and Functions 1.6 Control Panel Symbols Figure 1 to 4 below shows the detail of the panel push buttons. Of particular note to this course is the directional arrowhead on push buttons giving information about their use as the start (entrance) or finish (exit) of a route. The button surround may be of a different color according to the button function (main or shunt) and direction of traffic (up or down).   2. PUSH BUITON INTERLOCKING   2.1      Operation of Entrance-Exit (N-X) Panel   In route control system of signaling, a route is set and the signal leading over it cleared by the signal man operating two pushbuttons which are located on a control panel .The first button operated is at the commencement(Figure 1)  of the route and the second button at the finish(Figure 2) of the route .The finish button is generally at the next signal applying to the direction of traffic being dealt with, but in the case of a route which leads into a section, siding or terminal road the finish button is located in the section, siding or terminal road. Providing all conflicting routes are normal the push button operations are registered and any points in the required route which are not in the correct position will operate, then providing the line is clear to the clearing point, the signal will exhibit a proceed indication. If a conflicting route is set or a previous train is passing over points within the route and the points are out of position for the next movement, the button operation is not registered, and it will be necessary for the signalman to again operate the buttons when the route is free. To clear the next signal the last button operated which represented the finish of the previous route is again operated and acts as a commence button for the next route. A second button is then operated to locate the finish point for this route. After the passage of a train, or if it is required to cancel the route, without the passage of a train, the commence button for the route must be pulled to restore the route to normal. A signal cannot clear for a second train unless the route is normalized and then set again. If a button has been pushed as a commence button and for any reason the route which was to have been set is not required, the commence action may be cancelled by pulling that button. Only one button may be effectively pushed at a time and when operating a button as a finish button it should be depressed for approximately one second. The entrance-exit (N-X) push button panel is the standard type used by British and NSW Australia, and widely used elsewhere. The method of operation to set a route is: - Press the entrance (start) button and release it. The button will flash to indicate it is the selected entrance. The next button pressed must be the exit or finish of the route, and provided the route selected is both valid and available, the route will be set and locked, and white route lights will indicate the extent of the route set. The entrance button will display a steady white light. If an invalid exit or an unavailable route is selected, the route setting will be aborted. Because some buttons may function as both start and finish buttons (Refer Figure 5), and since the start signal may have several valid routes, each with a different finish, a constraint is imposed that only one route may be selected at a time. Where this would be over restrictive, several independent push button interlockings will be provided, one (or more) for each signalman's control area. In below figure 5, button for Signal 2 is a finish button for route from Signal 1 and is a commence button for route leading to Signal 4 and 6   LEGEND  Note: When relay is energized (Up), front contact will be made(close) and back contact will be open, similarly when relay is de-energized (Down) front contact will be open and back contact will be made (Closed) Some relays will be Normally Energized (EG: USR, ALSR, Track Relay), whereas some relays will be Normally De Energized (EG: DR Relay for Control Signal to show green aspect) Non Vital Relay contacts are same ,but dot  on each end of  armature ,thats how we identify  2.2            Push Button Relays   All push buttons on a panel have three positions, middle (denoted 'M'), pushed (denoted 'F' - meaning "from" the operator) and pulled (denoted 'T' - "towards" the operator). The button is sprung to return to the middle position after it is either pushed or pulled. Depending on the exact function of the button, relays will be provided to repeat the relevant positions or combination of positions of the button. Refer figure 5 for the most common circuit. To set a route from No .1 Signal to No.3 (M) Signal, button No 1 (for Commence) is pressed, energizing 1(FR) relay   The diagrams show these relays wired direct to the panel button. This is the normal arrangement for the local interlocking at the control centre. For other interlockings, a remote-control link, normally TDM, is employed. Refer Figure 7. Any Telemetry such as Kingfisher also could be used. Traditionally control system is non vital system used for route request and indication of equipment status back from the track.   2.3 Push Button Checking Circuit   At various stages in the route selection process, it is necessary to prove that only one button is being pressed. This is accomplished using the (R)PR circuit sample shown in Figure 8 The (R) PR provides the interlocking between buttons to ensure only one button operation is registered at a time. 1(F) R contacts make, energizing 1(R)PR relay. This lifts 1(R)PR contacts cutting out all other (R)PR Relays Back contacts of all following (R) PR relays are included in the negative side of each (R)PR relay to prevent it picking up if its button is operated (F) R energized whilst any following (R)PR is already energized. Thus, ensuring only one button operation will be registered at a time. 2.4 Pressing the Commence Button   The interlocking will store the signal selected as the start of the route by holding the appropriate CeR up. Refer Figure 9 The CeR initiates the commence operation to set a route. 1(R)PR contact makes, energizing 1CeR relay. 1CeR stick contact is made and holds 1CeR relay energized when 1(R)PR drops out (ie when commence button No. 1 is released) via 1(N)R & FnJP2R contacts. 1(N)R contact is a route cancelling contact which energizes when a button is pulled and the FnJP2R contact (2nd repeat finish normally closed relay) forms part of the timing cycle circuit. These circuits will be covered later. As 3 buttons can be either a commence or finish button, 3FnR (Finish Relay) is proved de­ energized in its commence relay circuit. 2.4.1       Machine in Use The MUR sets circuit operation to ensure the next button operated initiates the finish operation for the route. 1CeR contact picks up and energizes the MUR relay whose contact turns MUR indication light on (flashing red). The FnPR contact ensures that the MUR is held energized to prevent the MUR from dropping out if a finish button is held longer than one second this would change the button from finish to a commence function (Refer Figure 13). In Figure 11 MUKR is a repeat of the MUR and the FnPKR is a repeat of FnR, Refer  Figure 12 This gives a flashing red or green indication on the console which indicates to the signalman whether the machine is in use or finish. When FnJP2R relay drops out 1CeR relay de-energizes, thus extinguishing the MUR light. Refer Figure 14. 2.5  Pressing the Finish Button The finish of the route will be identified by one FnR energized. The combination of CeR and FnR uniquely identify the route. Refer Figure 7 above. To select destination (finish) in this case there is only one possible destination from Signal 1 which is No. 3 signal. Pressing button 3(M) for finish, energizes 3(M) (F)R. The (FM)R relay provides for emergency replacement of a signal after the route has been set. Refer Figure 12 for Finish Relay (FnR) Circuit   The FnR initiates the finish operation to complete the route being set. When the 3(M) (R)PR energizes, and because the MUR relay is already held up via No. 1 CeR as shown Figure 10, 3FnR relay energizes for the period of time that the button is held in. As No. 3 button can be either a commence or finish button, both commence relay functions, 3 & 3 (S), are proved down in its finish relay circuit. This holds the FnR de-energized during the commence function when the MUR has picked up and while the (R) PR is still energized. 2.6 Push Button Circuit Normalization Approximately 1 second is allowed before the push button circuits are normalized, to permit setting of another route. This prevents preselection by the selection of the commence and finish signals before the route is available. Figures 13 & 14 show the normalizing circuits. The FnPR (finish repeat relay) initiates the timing sequence for a route to set. Refer Figure 13 for Finish Repeat Relay Circuit. When 3FnR contact makes, and energizes the FnPR relay the timing cycle, of approximately one second commences and, in this period the route must be capable of setting. If the route is not capable of being set within one second of the signalman operating the finish button, the action is not registered and the entire operation for setting a route must be commenced again. The FnJP2R and the stick function of the FnPR maintain the FnPR energized if the finish button is released before the timing cycle is complete to allow the timing cycle, once commenced to once completed. The FnJR & FnJPR's (finish timing relays) provide the timing sequence initiated by the finish function. The FnPR energizing starts the timing cycle through the slow to drop relays FnJR, FnJPR & FnJP2R. When the FnJP2R relay drops out a number of things occur: The CeR relay is dropped out via FnJP2R contact in the stick path circuit as shown on Figure 9. The MUR relay is dropped out via the CeR contact dropping out in circuit as shown on figure 10 The FnPR relay drops out if the finish button is released in circuit shown on figure 13, via the FnJP2R de-energized in its stick circuit. This timing sequence provides the non-storage feature of the system. (i.e routes cannot be pre­ selected until a train has vacated the route). 2.7 Effect of Pressing the Wrong Type of Button   Pressing a finish only button at the start of route setting will have no effect because the signal does not possess a CeR. The circuits will normalize as soon as the button is released. Pressing the incorrect finish button will result in no route being set as the FnR and the CeR previously selected will not both appear together in the same route setting circuit anywhere in the interlocking. 2.8 Indications Panel   To assist the signalman indication lamps are provided to show "machine in use" or "machine finish" to advise him of the current state of route setting. On many BR interlockings, the technician is provided with the facility to hold the equivalent of the FnJP2R energized to assist fault finding. This enables him to test circuits which otherwise may only be energized very briefly. This facility must be used with great care, and with the agreement of the operator, as it will inhibit the setting of any other route in the interlocking. 2.9 Route Control System-Route Setting Having now dealt with the operation and circuits associated with the control panel switches, we will now cover the operation and / or function of each relay, for the setting of the points to the correct position, locking them, setting the required route, and clearing the appropriate signal leading over that route which will include route locking and approach locking etc. Refer Figure 18 & 19 2.10 Route Setting When a button is pushed to select the commencement of a route (R)PR energizes & providing that no other button has been pushed a contact on the (R)PR closes the circuit for the 'commence relay' CeR, (Refer Section 2.4). A front contact of the CeR then energizes the 'machine in use' relay MUR (Refer Section 2.4.1). The MUR energized opens the pickup circuit for all CeR's & this determines that the next button to be pushed will function as a 'finish' button. The CeR for the button operated is held energized by a stick circuit which includes a front contact of the finish timing relay FnJR, back contacts of its own (N)R relay & its own front contact. When the next button is operated to define the finish point of the route to be cleared, its  (R)PR is energized & because the MUR is up, the finish relay FnR (Refer section 2.5) for that button will energize for the period of time that the button is held in. A circuit is provided for the MUR via a front contact of FnPR, the finish relay's repeat relay, to prevent the MUR from dropping out if a finish button is held for longer than one second. (This would change the button from a finish to a commence action). Contacts of the CeR & FnR relays in series are utilized in the negative side of the route NLR delatching coil and drive the relay down this in turn closes the circuit for the route RUR and providing all locking and track circuit conditions are satisfactory the route will set and its signal clear. (Refer Section 2.12). The commence relay CeR and FnR (finish relay) remain energized for approximately one second after the finish relay has operated but long enough to allow the route NLR to delatch and the RUR to energize.  This sequence provides the non-storage feature of the controls.   That is, if the route is not capable of being set within one second of the signalman operating the finish button, his action is not registered & he must operate the buttons again when the route is free. The method of obtaining the one second timing period is as follows. When a finish relays FnR energizes, its front contact completes the circuit to the finish repeat relay FnPR (Refer Section 2.6) & a back contact of the FnPR opens the circuit to the finish timing relay (Refer Section 2.6). The three finish timing relays are slow-release relays & approximately one second after the FnPR has energized the FnJP2R opens its front contact to break the holding circuit for the commence relay network (CeR). (Refer Section 2.4). A stick circuit is provided to hold FnPR energized until FnJP2R is de-energized.   This ensures that if the finish button is released before the timing cycle has been completed, the FnJP2R will still release & cancel out the CeR. When the commence relay releases & the finish button has been released the MUR releases, and with the timing relays energized & all button relays are in their normal position the system is ready for another route to be set or for another attempt to be made to set the same route. 2.12 Route Normalizing The (N)R Relay controls(Refer Figure Below) the normalizing of the appropriate route NLR, and when energized, drops the route reverse relay (RUR), and latches up the route normal relay (NLR). Refer below figure 20  for a typical (N)R Circuit  Figure 20 Normalising Relay  When No. 1 button is pulled, 1(N)R is energized and is held up by a back contact of the route NLR which is to be normalized, a back contact of 1 CeR and its own contact.  The stick circuit will maintain 1(N)R energized until the route NLR circuit is completed by the signal returning to stop or the approach stick energizing as the case may be. The push button can therefore be released immediately after it has been pulled. Once the route NLR has latched up, its circuit is opened by the (N)R relay dropping & it is held in the up position by its magnetic latch. The back contact of the CeR in the (N)R stick circuit permits a signal to be recleared, if required, after it has been cancelled but the route has not normalized due to approach locking. A back contact of the (N)R relay is wired in the stick circuit of the relative CeR relay & this allows a button which has been incorrectly pressed as a commence button to be cancelled by pulling the button. 2.12 Checking Route Availability & Validity   The Commence and Finish selected by the signalman, stored as CeR and FnR, must now be checked for validity - physical route possible - and availability. Normal lock and reverse route relays are provided for each possible route in the interlocking. These circuits comprise two parts. To the right of the relays (in the negative feed) are the relay contacts which respond to the push button circuits. The validity of a route is proven by the presence of a circuit with the correct CeR and FnR combination. Refer Figure 15 The availability of the route is checked via the positive feed where all locking is proved. An example of a route with points is shown on Figure 16. The points must be in the required position (NLR or RLR up) or free to move (WZR up). Providing the route is available the NLR will unlatch and allow the RUR to pick and stick. This operation must complete within the 1 second before the push button circuits normalize. In the event of the route not being available at the time of selection, or within one second, the push button circuits will normalize. The selection is not stored until the route becomes available but can only be acted on at the time of selection. 2.12.1 Route Lock Relay (NLR/RUR) Each route in the interlocking from signal to signal or from signal to section, siding or terminal road has a RUR to set points and clear the entering signal and a NLR which proves the route normal and is used in locking conflicting routes. The route lock relay circuits for No. 1 route are shown on Figure 15. The route RUR and NLR circuits are electrically interlocked with each other. Thus, 1NLR back contact is in series with 1 RUR operating coil and 1RUR back contact is in series with 1 NLR operating coil. The NLR is a magnetically latched relay and remains latched in its last operated position. It has two coils, one to latch the relay up, and another to latch the relay down. The operation is described on section 2.12.2  The route NLR when latched up is used to release conflicting routes, and proves that: - the signal has returned to stop the signal is not approach locked the route RUR is de-energized & is therefore not capable of setting points or clearing the controlling The route RUR when energized proves that the route NLR is latched down thereby checking that all conflicting routes and points are locked prior to the route setting. The interlocking between routes is carried out in the positive leg of the RUR relay in accordance with the locking table for the interlocking. If a route requires that certain other routes must be proved normal before that route can set, then normal contacts of the conflicting route NLR's are included in the positive side of the RUR for the route concerned. The interlocking between routes and points is also carried out in the positive leg where a contact of the points NLR or RLR is included and qualified by a contact of the WZR for the points concerned if the points are out of position but are free to move. Note: Positive leg of the route locking relay circuit included the interlocking function (Safety Function) and negative leg of the relay circuit included the route selection (Non Safety Function) Refer Figure 17 for sample control table. Routes and point conditions reflected are the logic for the positive limbs of the RUR/NLR circuits referred in Figure 15/16. Eg: Front contact of Route 9C NLR will be in series with 1NLR and 9BNLR, where 1NLR is qualified(parallel) by point 103NLR and 112 RLR and 9BNLR qualified by Point 112RLR. This will be in series with Points required/free to move Normal or Reverse 2.12.2 Route Lock Relay Circuit Operation (NLR/RUR) Refer Figure 15, when the commence and finish push buttons have been operated to clear No 1 signal, 1 CeR and 3FnR contacts will be up together as described in Section 2.4 & 2.5. This drives 1 NLR magnetically latched relay down and closes 1NLR contacts. This action then completes the circuit for 1RUR relay to energize via 1 CeR and 3 FnR contacts. Front contacts in the negative leg of 1 RUR circuit then close, and hold the relay energized via 1(N)R and 1 (FM) R normalizing contacts after 1 CeR and 3 FnR have dropped out at the completion of the timing cycle. The route will remain set until the commence button at No 1 signal is pulled, which will pick up 1 (N) R contact and open 1 (FM) R contact. If the ALSR relay is de-energized, ie, the route is approach locked, the route cannot be normalized to release the interlocking. However, it may be re-cleared for the train to proceed. 3 POINT CIRCUITS   3.1 Principles of point operation   Points may be called to operate by one of two methods: - a) The setting of a route requiring the points to be moved using route setting  buttons, or - b) The operation of a point key (lever) on the panel. At the time of calling, the points must be free of locking in their present position. Points may be locked by route locking, track circuit occupation, the point key having been turned, or another route having been set. The points must be free at the time of selection, and the selection must not be stored until the points become free, (anti-preselection). In the event of a power failure the last legitimately selected position of the points should be held, and, on restoration of the power, the points should not be called to another position due to the random recovery times of different relays within the interlocking.  3.2 Calling the Points   Figure 21 shows a point Lock relay (NLR/RLR) circuit. It has two halves. Setting contacts are in the negative feed and locking contacts in the positive feed.   At any one time only one Lock relay should be up corresponding to the position to which the points were last called. Unlike the route lock relays, both NLR and RLR are latched relays. There is no distinction in safety terms between the normal and reverse positions for points. Except in special circumstances, points controlled from a route setting panel are not returned to the normal position after use. 3.2.1 Lock Relays   The points normal lock relay (NLR) and points reverse lock relay (RLR), perform route and interlocking functions associated with the points, they also control their operation. On operation of the control panel buttons to set a route, the RUR is energized, providing the interlocking is free. The RUR contacts then set all necessary point lock relays which in turn operate the points to line up the route. With point detection indicating that the points are in their correct position and providing that the track circuits concerned are clear the signal control relay energizes via contacts of the RUR and button normalizing relays. These relays are magnetically latched and remain in their last operated position. Therefore, before picking up one relay, it is necessary to energize the release coil of the other. This is accomplished by wiring the negative side of each release coil to the negative side of the operating coil of the other lock relay. As each lock relay operating coil is wired through a back contact of the opposite lock relay, one lock relay is proved down before the other lock relay can energize. Therefore, before a points lock relay can be energized to drive the points to the next position, the lock relay for the existing position is proved down ensuring that all routes which lead over the points in their present position are normal before the points can move. In the positive leg of the points NLR and RLR is the interlocking function between the points, and signals which lead through the points. Route (track) locking over the points, including selective overlap (tracks which will allow the points to operate to the vacant overlap), and back contacts of the opposite points lock relay, and detector relay, to prove those functions de­ energized before the lock relay concerned will operate. In the negative side of the NLR circuit are RUR contacts of all routes which will set the points normal in series with a contact of the points (C) R (Lever Centre Relay) and in the RLR circuit, RUR contacts of all routes which will set the points reverse, together with a point (C) R contact An alternative path is also provided for use when the points are to be operated under lever control for both normal and reverse operation.  3.2.2 Circuit Operation When a call is placed on 101 points to operate reverse, e.g., 3M(A) route has been called, 3(M)A RUR will energize closing the negative leg for 101 NLR release coil and 101 RLR operating coil via the lever centre relay (C)R, to negative. Providing the points are free to operate, i.e., 101 WZR (points free relay) is energized, indicating that the interlocking is correct, and the track circuits through the reverse route are clear, 101 NLR will be driven down via front contacts of 3M(B) & 3(S) B NLR, 3ATPPR and 3XTPR tracks (interlocking and track locking for the reverse route) 101 NLR and 101 WZR and WJR. This action closes a back contact of 101 NLR in the positive leg of 101 RLR operating coil, proving the NLR has de-latched and allowing the RLR to energize (latch up). A front contact of 101 RLR now connects the WZR to 101 NLR circuit in readiness for the points when called to operate normal. 3.3 Locking Circuits The positive feed to the NLR/RLR circuit checks the availability of the points to be moved, either normal to reverse or reverse to normal. The feed to the WZR can be obtained from either the normal or reverse branch of the circuit, dependent only on the present state of the NLR and RLR. If WZR is able to energize it shows the points are free to move from their present position. 3.3.1 Point Free Relay (WZR) & Point Timer Relay (WJR) The WZR or points free relay(Refer Figure 21)  is a slow to release relay to prevent the RUR from dropping out during the operation of the points lock relays. It taps off the interlocking and track locking portions of both NLR and RLR. When the NLR is energized the WZR detects if the points are free to move reverse. When RLR is energized the WZR detects if the points are free to move normal. Thus, the WZR relay when energized indicates if the points are free to operate to the next position. The WZR is used to convey this information to the route RUR circuits which are allowed to energize if the required point lock relay is energized or if it is free to be energized. A point timer relay (WJR) is provided to ensure that the tracks have been free for a length of time to cover "bobbing" tracks. The WJR(Figure 21)  is a slow pick-up relay, which together with the slow pick-up track repeat relays provides a two-stage timing before the points are free. The WJR is tapped off the points lock relay circuit, and a contact of this relay cuts the WZR. The WJR is provided in the NLKPR and RLKPR circuits. (Figure 21). A contact of the WZR is also used to illuminate the points free light above the centre of the lever and indicates to the signalperson when the points lever may be operated to drive the points to the next position. The only interlocking information not conveyed by the WZR relay is the point-to-point locking and this is added to the points free light circuit. The WZR relay and WJR point timer relay in conjunction with the transient nature of the button controls provides for non-storage operation of the points under route setting conditions. If when the buttons are pushed to set up a route, the point lock relays are not in the correct position or free to be operated to that position as indicated by the WZR relays for the one second period during which the button relays are energized, it will be necessary to operate the buttons again when the route is free. If a train were passing over points within the route in question the security of the points is dependent entirely on the track relays remaining down whilst occupied by the train. Therefore, if the track relay should "bob" during the one second which the button relays are energized the points would commence to move under the train. To guard against this event, track repeat relays are made 4 seconds slow operating so that local tracks in the point circuit must be clear for 4 seconds before the points become free to operate to the next position. 3.3.2 Lock and Detector Repeat Relays (LKPR) Refer Figure 21 .The circuits for these two relays which tap off the points lock relay circuits are the points Normal and Reverse lock and detector repeat relays (NLKPR and RLKPR). Contacts of these relays are used in the signal control circuits to provide proof that the detection and lock relays are in their correct position and that the operation of a route RUR has locked out the points lock relay for the movement to the next position before a signal can clear. The NLKPR taps off the normal lock relay circuit so that it includes all interlocking which prevents the points from driving normal. In the case of 101 points, 3(M)"A" and 3(S)"A" NLR's, proving that routes which require 101 points reverse are normal. It ensures that 101 NLR and 101 NWKR are normal. It also ensures that 101 ROLR, 101 RLKPR, 101 WZR and 101 WJR are de-energized by back proving contacts. The proving of 101 WZR de-energized is most important, and its function is as follows. With 101 NLR energized (latched up), and 3(M)"A" route is called, the release coil of 3(M)"A" NLR is energized when the commence (CeR) and finish (FnR) button relays are operated and when 3(M)"A" NLR makes its back contact, 3(M)"A" RUR is energized. When 3(M)"A" NLR opens its front contact the circuit for 101 WZR and 101 NLR is opened and 101 WZR drop contact makes to allow 101 NLKPR to energize and complete No. 3 signal HR circuit. Therefore before No. 3 signal can clear proof is obtained that 101 RLR circuit is opened via 101 WZR de-energized and therefore 101 points cannot be operated to the reverse position. 101 RLKPR taps off 101 RLR circuit and performs similar functions to 101 NLKPR, being utilized in signal control circuits which lead over 101 points in the reverse position. 3.4 Calling the points by route setting   Energization of an RUR in the negative feed of the lock relay circuit will set the points provided the point key is central and the points are not locked by other routes, track locking or route locking. Energizing the RUR will have proved that the points are in position or available (e.g., NLR or WZR up for a move to the normal position). Contacts of the RURs for each route shown in the control tables to set the points will be wired in parallel in the NLR or RLR negative feed. Conversely the NLRs for the same route must be included in series in the positive feed of the opposite lock relay. 3.5 Moving the points using the point key/lever Relays (N)R and (R)R repeat the panel key/lever in the normal and reverse positions respectively. They allow the points to be moved individually. It is important to note, WZR must be up at the time of setting with the point key or the points will not move, even if any locking is later removed. Therefore, when moving the point key from normal to reverse (or vice versa), it must be held momentarily in the centre position to allow the WZR to reoperate. 3.6 Points in Overlaps There are situations, generally where swinging overlaps are involved, in which the simple use of route RLRs to call the points is not sufficient. Relays NOLR and/or ROLR may be provided to give the required point setting commands Refer Figure 22. Overlap relays automatically set facing points in the overlap of a signal to give a clear overlap for that signal. When a route which has facing points in its overlap is set and the points are lying so that the overlap over which the signal would clear is occupied, but an alternate overlap is clear and the points are free to operate to that overlap, the overlap relay OLR will energize and drive the points to that position. The controlling signal for the route then clears via the free overlap. The OLR relays are only energized during the one second period that the button relays are energized and thus comply with non-storage requirements. Protection against the OLR's causing the points to move if a track relay should bob under a train is obtained by wiring a contact of the relative point WZR relay in the OLR circuit, thereby ensuring that the points have been free for at least four seconds before they can be operated to another position. If the points in the overlap of a route are not free to move to an unoccupied overlap when the route setting buttons are operated, the route RUR will energize providing its requirements are met but the OLR will not be energized. Because of the transient nature of the button controls it will be necessary to either re-operate the buttons when the points become free or to set the points to the required position by operating the point lever. 3.7 Point Operation & Detection The position of the NLR and RLR in the interlocking must be translated into a command to the points to move to or remain in the corresponding position. This is done by means of a polarized circuit to the NWR & RWR at the location. A typical circuit is shown on Figure 23. Points control is affected through the NLR and RLR. Contacts of the relevant lock relay operate the normal points contactor (NWR) or reverse points contactor (RWR). The points contactors can be of the type that are mechanically interlocked with each other and are installed in the points locations, or polarity sensitive relays installed in the points location or provided within the point machine, and which will only energize if the polarity of the supply to the coils is correct. Relays installed in the points location are type QBCA1 and have two heavy duty front contacts that are capable of switching about 10 amps current to the point motor. Referring to the circuits above, each contactor is double switched by contacts of the points lock relay concerned. The points NLR when latched up will pick up the normal contactor and the points RLR when latched up, will pick up the reverse contactor. The opposing lock relay is proved down in the relevant contactor circuit in each case. This provides a measure of safety so that if both lock relays should be up at the same time or if either lock relay is unplugged both contactor coils are open circuited. When energized the motor will run either normal (if NWR energized) or reverse (if RWR energized). They are polarity sensitive relays, usually QBCA1 and will only energize if polarity i s correct. Positive to R1 and negative to R2 contact. These relays have two heavy duty front contact which are capable of switching about 10 amp current on and off to the point motor. They are energized by the NLR energized and RLR de-energized in the case of the NWR, and the NLR de-energized and RLR energized as in the case of the RWR. These contacts are double cut into the point relays, ie contacts in both positive and negative feeds. Each relay is also controlled by the opposite relay being de-energized, ie RWR proved down in NWR circuit and vice-versa. There are two contacts of each relay in the opposite circuit, ie: referring to the circuit diagram RWR A6/A5 and D6/D5 are in the NWR circuit. This is to prove that the whole relay is de­ energized as it is possible to have half the relay 'stuck-up' by failure of a set of contact strips. Relay rows A and B are operated by one strip from the armature and relay rows C and D from another. This then proves that the RWR is definitely de-energized before the NWR can pick and vice-versa. Once the points have moved to the correct position, a polarized detection feed comes back to energize NWKR or RWKR (Figure 24) provided the detection corresponds to the position required by the interlocking (NLR/RLR). The detector relay circuits (NWKR & RWKR) as well proving that the points  have corresponded to the lever and are locked (via NKR or RKR), also proves the following:- The opposing WKR de-energized, via a back contact  The corresponding NLR or RLR energized, thereby ensuring all interlocking functions are correct  The LWR (E.P. points,NOT SHOWN ) or Isolating Relay (electrical points) de-energized via back contact . This ensures that the points cannot be operated, except under normal operating conditions. For EP. points (Not shown here) that the Plunger Lock has returned to the normal position (locked), via plunger lock normal contacts. This ensures mechanically that the points will not move should the control valve be falsely energized, or "creep" open due to worn equipment. For electrically operated points, a contact of the EOL is included to ensure that while the EOL is withdrawn from the lock for emergency operation of points, both WKR's are de-energized, thereby ensuring that the signals protecting the points cannot be cleared, or the points operated from the control With the points normal and called reverse, the points NLR is driven down and drops the normal detector (NWKR). A back contact of the NWKR closes the circuit for the points RLR, allowing the relay to latch up, providing that all interlocking functions are correct. This allows the points to then operate to the reverse position. The point operation circuit has the additional protection of the IR (isolating relay). Refer Figure 25. This proves all signals reading over the points normal, all direct locking tracks clear and no trains between the points and a protecting signal (unless moving away from the points. The WTJR (where provided) disconnects the circuit to the point contactors if the points have been running too long. This will avoid damaging the point motor or clutch if an obstruction in the points prevents them completing their movement.  IR's (for electrical operated points) or LWR’s (for E.P. points) prevent irregular operation of the points should the point lock relay, contactor or control valve be falsely energized whilst a train movement is taking place over the points. The IR associated with electrically operated points can be of the neutral contactor type or a polarity sensitive relay and is installed at the points so as to be physically remote from the points contactor to prevent manipulation, or in the points location where the points contactors are of the relay type and thus sealed or located in the points machine. The LWR is associated with E.P. points and is normally located adjacent to the points. When energized the LWR unlocks the facing point lock via the plunger lock and allows the points to move. The IR or LWR check that the home signals protecting the points are normal and not approach locked, and that tracks from the home signals to the points, and the local tracks over the points are clear before the points can be operated to the next position. When the points have reached the required position the IR or LWR is open circuited by either a switch machine contact where the contactor type is used, or the relevant local detector relay (NKR/RKR) energizing where polarity sensitive relays are used and proved de-energized in the detector relay circuit (NWKR or RWKR). Where polarity sensitive relays are used, for electrically operated points a contact of the EOL (Emergency Operating Lock) is provided and when operated manually, the isolating relay is open circuited. The NKR and RKR (Normal and Reverse indicating relays), are located locally at the points and prove that the points have corresponded to the lever movement and are locked. They are divide into (2) two basic circuit types, those for E.P. points and those associated with electrical operated points.  Figure 26 shows a typical NKR and RKR circuit used for electrically operated points using polarity sensitive relays. The points are proved Normal or Reverse and locked before the corresponding detector contacts are allowed to make. The opposing KR is also proved de­ energized via back contacts. 4 ROUTE LOCKING   4.1 Principles The control tables will often specify route locking to allow the route to be held in front of a train whilst being released section by section behind the train. This is effective as soon as the route is set and releases only after the passage of the train (or if no train has entered the route after the signal approach locking is released). 4.2 USR (Route Stick Relay) Circuits   The relays used to lock each part of the route are called USRs, Route Stick Relays, which are energized when that section is free of route locking in the direction specified, and de-energized when route locked. A typical USR circuit is shown on Figure 27   The presence of the JR contact in the circuit will depend on whether the control tables specify a timed release. The route stick relay in route control systems of interlocking performs a similar function to those in conventional interlockings where it may be used to: maintain or hold the route locking to provide maintenance of selective overlap. hold the route locking where a train has passed an outer protecting signal which is interlocked with the points, and the signal normalized with a train occupying the track circuits ahead of that signal. qualify that portion of the route locking that would not be required where the route is signalled for both directions. The route stick relay is a normally energized relay with a stick function the relay being held energized by the signal concerned at Stop (ALSR Energized). The relay is de-energized when the signal is cleared and will remain de-energized with the track circuit ahead occupied although the route has been normalized. The USR is dropped by the ALSR down (signal cleared) and proved de-energized in the signal HR circuit. Under certain conditions the USR may be required to be timed out to release the locking, and where this is required a front contact of the track time limit concerned qualifies the stick function to allow the relay to energize at the completion of the timing cycle. An example of the function of a USR relay is shown in Figure 21 where 1 USR is used to hold the points lock relay de-energized for maintenance of selective overlap.   5         SIGNAL ASPECT CONTROLS    5.1     Aspect Requirements   Once any route has been set, it must be proved entirely, including any overlap before displaying an appropriate proceed aspect and relevant route information to the driver. This may include track circuits and/or points depending on the type and geography of the route.  5.2 UCR Circuits   The UCR proves continuously that all conditions are present for the signal to clear. A UCR will generally be provided for each route. The UCR relays are mounted in the main location and include all the functions normally placed in the HR circuits. In effect the UCR is an internal HR relay. The HR relays are located in the remote locations. The UCR drops the NGPR and then the USR and ALSR relays which are proved down in the outgoing HR circuit, in series with front contacts of the UCR. The UCR relays allow proving of internal relays. UCR circuits will generally contain the following controls: - a) A contact of the relevant RUR which only operates when the route is required to set. b) The SR, which allows the signal to clear for one movement only  c) Track circuits proved clear by TPRs. For main routes, the tracks will be proved clear to the end of the overlap. Where facing points exist in the overlap, tracks beyond the facing points will have NWKR or RWKR contacts in parallel to exclude tracks when the points are set away from them . d) Points set and locked, using NLKPR and RLKPR contacts  Also shown in the circuit examples are back contacts of the TZR (this will be present when automatic nominalization is required) and down proving of any track circuit timers which will be used to release route locking associated with the route. Refer Figure 28 for a Route Checking Relay which the UCR circuit for No.1 signal where the route is proved set by the RUR being energized thereby ensuring that all interlocking is correct and all relevant track circuits, including selective overlaps are proved clear (energized). This Figure 28  shows the UCR circuit for No3 Signal has four routes     Main Route M(B) Shunt Route S(B) Main Route M(B) Shunt Route S(A) 5.3  Different Types of Routes   Where controls are common between different types of routes (e.g., 3(M)A and 3(S)A), part of the circuit can be common to both UCRs. In the example shown on Figure 28, the main route UCR will include track circuits, but the shunt route will not. Such circuits can often be laid out in a geographical manner. The circuit designer should decide the most efficient layout by reference to the signaling plan and control tables. Where main and shunt routes exist from the same signal, the track circuits and overlap points will have to be separated out to appear in the (M)UCR circuit only. 5.4 Stick Relay   The function of this relay is to maintain the signal at stop after the train has passed it. The signal will clear for one train movement only.  Once the train has occupied the first track in the route, the stick relay can only be reoperated by normalizing and resetting the route. If automatic working is required, an (A)SR will be provided to maintain the SR circuit energized. The lever stick relay (SR) performs the same function as in a conventional interlocking. When a train passes a signal, the signalperson must pull the panel button to normalize the route before the signal can be cleared again. Referring to the circuit Figure 29, with the passage of a train passed No 1 Signal 1, SR is de­ energized by 1AT track dropping and will remain down after the train has vacated the track until No 1 panel button is pulled to energize 1(N)R relay, where a pickup circuit is established via 1AT and 1(N)R contacts. 1 SR is held energized via 1AT track contact and 1 SR stick contact when the route is set by the operation of the panel button. A front contact of 1 SR is included in No 1 signal control circuit (1 HR or 1 UCR if provided) and after the passage of a train past No 1 signal the SR contact prevents the signal from clearing again until the route is normalized and then re-set by the operation of the panel buttons. The (N)R contacts in parallel with the route NLR contacts allows re-energization of the SR relay should power failure occur when a train is approaching the signal and the signal is showing a proceed indication, under which conditions the approach stick down would prevent energization of the route NLR (approach locking) when the panel button was pulled and it would not be possible to energize the SR relay to re-clear the signal unless the timing period of the ALSR had elapsed. 5.5 Approach Lock Stick Relay (ALSR) 5.5.1 Approach Locking (Requirement) Approach Locking is achieved by means of an Approach Stick Relay (ALSR) and is provided on all controlled signals with the exception of certain starting signals. Its purpose is to hold the route locked, thus preventing the operation of points in the route and/or the setting of a conflicting route if the signal protecting the route has been returned to stop in the face of an approaching train. A route becomes approach locked once a driver has seen a 'proceed' indication or has seen an indication at a previous signal which would indicate to him that the next signal is displaying a 'proceed' indication. Where long sighting distances are involved, 600 meters is considered a suitable approach locking distance to the first warning signal. The approach stick relay is energized by front contracts of the NGPR i.e. signal at stop, and the approach track or tracks circuits to that signal unoccupied and will remain energized with the signal at stop via the stick path with the approach track occupied. The relay is de-energized when the signal for the route is cleared and will remain de-energized with the approach track occupied although the signal has been normalized. A front contact of the approach stick relay is included in the route NLR and prevents this relay from normalizing (latching up) when approach locking occurs as described above, thus preventing release of the interlocking. When a route becomes approach locked it is impractical to hold the route locked indefinitely once the train has come to a stand. To overcome this and the need for the signal electrician to provide a 'release', a time release relay is provided (ALSJR). The relay commences its timing cycles once the signal has been returned to the stop position (NGPR) energized. A timing cycle of 120 seconds is provided for main line running signals and is considered sufficient to ensure the train has come to a stand. For shunting signals a time limit of 60" is provided. A front contact of the time release relay is placed around the stick function of the ALSR and when energized allows the ALSR to energize. 5.5.2 Approach Locking (Operation) The circuit for 3 ALSR as shown on Figure 30,and its various circuit paths are as follows: PATH No 1:- 3 ALSR will energize (approach locking not effective) if No 3 signal is at stop, (NGPR energized) and track circuits approaching No 3 signal (1AT and 1BT) energized, with the approach track to No 1 signal (54.5B) included if No 1 signal has not normalized (1 ALSR down). This arrangement satisfies the condition where a driver has seen an aspect at a previous signal which would indicate to him the next signal is displaying a proceed aspect. The two-track occupation to release approach locking under normal running conditions is to overcome the problem of a track bobbing under a train thus releasing the locking. PATH No 2:- Allows for energization of 3 ALSR when a train proceeds past No 3 signal in the normal manner and allows a release of approach locking should a long train be standing with its rear on the approach locking tracks. To guard against a release due to an intermittent failure of 3AT, either 3BT or 3XT must be shunted at the same time. To guard against a premature release due to a power failure and restoration, which will cause the track circuit PR’s to drop and then pick up, a front contact of POJPR, a power off time delay relay, is included in the release path. The POJR, which is the parent relay for the POJPR, is wired directly across the AC supply and does not make. Its front contacts until 30 seconds after the supply is restored. PATH No 3:- The stick circuit holds the ALSR energized with the protecting signal (No 3) at stop and a train occupying the approach tracks. PATH No 4:- Energizes the time release which allows the release of the approach locking when the signal has been cleared and then returned to stop with a train occupying the approach tracks. 5.5.3 Approach Locking (Testing )  There are 4 approach locking test performed in the logic. Test1: Did the signal always stay at stop ?That is,  signal not shown a proceed aspect .Then it is safe to normalise the route when controller cancels the route  ,test passes and route get cancelled straight away Test fails if signal started to clear or made an attempt to show a route indicator and if lamp is failed ,driver believe a proceed aspect. Test 2 : Has no Train approached the signal ?Its is permitted to cancel (normalise) ,if approach tracks are clear (ie .Upto sighting distance of first caution-Comprehensive Approach locking ) .This means if no train approached test passes and route  get cancelled .If Train has approached the signal and controller put signal to normal ,test fails .This is checked for the track status from concerned signal looking back to first caution aspect (Comprehensive approach locking ) .Test 2 is required only when route is not approach controlled for Red (MAR ) or an automatic working facility. Test 3:-Did Train enter the route ?If signaller cancels the route when train  entered the route already ,test passes because sectional route locking will protect the train (USR relay above ) .Test fails when route is cancelled while train occupy birth track and just entered .Sectional operation of track is 1st track clear ,2nd track  occupied ,AFTER first track occupied and second Occupied  Test 4 : Did Train get Time to stop?.This is the last resort to normalise the route ,if all above 3 test fails when test sequence started and train seen a proceed or impression of proceed aspect .Then timer operates for the train to come to standstill OR  have to wait for train to pass the signal for sectional route locking to release (USR) .In UK practice for a Main Signal Timer is 180 seconds for comprehensive approach locking and 120seconds for Signals get approach locking "when cleared"   and in Australia it allow only 120 seconds for a train to come to standstill for main routes  or 60 seconds for shunt route  and approach locking get released after timer times out (Timer path on the ALSR relay ) .In nutshell for main line or loop line timer value is based on the class of route (Main Route  /Diverging Main Route) ,which is 180 seconds for UK and 120 seconds in NSW ,Australia. If the route is Call on (Position Shunt Route  ) ,irrespective of straight route or shunt route approach release timer value will be lesser .Check with your railway for these values ! 5.6  Signal Operation   The UCR is at the interlocking. This will be used to operate a circuit to the HR at the location, controlling the clearance of the signal. Refer Figure 31 for a typical HR circuit for 1 Signal and 3 Signal where 3 Signal have both Main and Shunt routes. The HR (Signal Control) Relay operates the signal lights to show a proceed indication from the Stop position and is located at the signal location. The NGPR which proves the signal and train stop, if provided, have returned to normal, is proved de-energized in the HR circuit via back contacts. The ALSR and ALSJR are proved de-energized and ensures that the approach locking requirement is effective. The USR where provided is back proved thereby ensuring that the route locking is effective. The UCR proves that all points are detected in the correct position and that the track circuits are unoccupied for the route set. Refer Figure 32 for a Typical Signal Control Relay (DR) for green aspect. The DR Relay when energized provides the full clear (green) indication in the signal. The relay is energized by a front contact of its own HR and the HR for the signal in advance. Where single light colour light signaling is used, a front contact of the ECR for the signal in advance is included. This ensures that if a lamp fails in the signal in advance, the signal will only display a caution indication. The VRR of the signal in advance is also included when train stops are provided. To prove that the signal has responded to the interlocking control, an NGPR (signal normal - at stop) and an RGKR (signal cleared) are fed from the signal location back to the interlocking. The NGPR (Normal Signal Repeat Relay) proves that all signal control and operating functions, ie:- UCR's HR's and train stop if provided, have returned to the normal position, signal showing stop indication. The NGPR conveys this information via a front contact to the ALSR for the necessary proving, and the stop indication for the signal repeater in the diagram. It is also proved de-energized in the signal HR circuit. The (RGKR) Reverse Signal Indicating Relay, indicates that the signal has been cleared and is energized by front contacts of the HR relay concerned. This relay provides the clear indication for the signal repeater. Refer Figure 33 for Normal /Reverse Signal Repeat Relays Proof of signal normal is vital in the approach lock release. Both relays are used to provide control panel indications.    6 ROUTE RELEASING   6.1        Principles   Route releasing comprises the following sequence of events: - A) Initialization of route release - signalman pulls the signal button at the start of the route .If automatic normalization is provided, this will be initiated by the train passing the signal. B) Release of approach locking on the signal - the train is proved past the signal (this may occur before  or after (A)), the train  has come to a stand  at the signal or there is no train approaching. C) Release of the route up to the rear of the train, if any, known as sectional route release. 6.2 Approach Lock Release   As far as the circuits are concerned, the first step must always be to operate the ALSR. The circuit is shown on Figure 30 above. Three separate circuit paths are provided to pick the ALSR according to whether the train is entering the route, the train has come to a stand at the signal or there is no train approaching. The arrangement of this circuit will be determined by the "approach lock tracks" and "approach locking released by" sections of the control table. Once operated, the ALSR will remain up until the signal is ready to clear again  for another movement. 6.3 Route Release   Picking the ALSR will allow the NLR to latch up (Refer Section 2.12) provided the route has actually been cancelled.  This, in turn, will allow the USR (or the first USR if there is more than one) to pick as soon as the tracks are clear. It can therefore be seen that the route locking will always release behind the train. If the route is cancelled with no train, the USRs will pick up immediately as all the tracks are clear. 7. OVERLAPS   7.1 Principles   Interlocking circuits are considerably complicated by overlaps. The controls must be accurately specified in the control tables and then translated into additional calling and locking circuits. The circuits must ensure that any route requiring an overlap has that overlap (or an acceptable alternative) maintained as long as the route is set or there is a train in the route. 7.2 Aspect Circuits   The UCR circuit will include the additional point detection and track circuits in the overlap. For signals with facing points in the overlap, all valid overlaps will be included, with the necessary conditions of the position of the facing points. The facing points themselves will only be detected where they are set and locked to prevent a confliction with another route. 7.3 Route Locking of the Overlap   Where an overlap is provided, route locking must extend to the overlap. Normally a timed release is necessary to prove the train has come to a stand and allow the overlap to release when no route has been set forward from the next signal. The USR will then include a TJR contact for the last track in the route in parallel with the TPR front contacts. 8 PRESET SHUNT SIGNALS   Occasionally a preset (or facing) shunt signal is positioned within another route. It may either be operated on its own as a shunt signal or cleared by setting the main route (presetting). Once a train has entered the main route, the preset shunt must remain off until the train has passed it. The preset shunt may be replaced to danger in emergency, but this will not permit any release of the main route beyond the preset shunt. The examples do not include a preset shunt signal. The main points to note are as follows: - a) Main routes which require the shunt signal to be preset will first prove that the corresponding routes from the shunt signal are not in use (and vice versa). b) Setting of the main route will initiate the presetting process. c) The main signal will prove the shunt signal cleared in its UCR circuit. Pulling the signal button of the preset shunt will therefore return the main signal to stop. d) Route locking for the main route will be effective to the end of the route, not just to the preset shunt signal. Once the train has entered the main route, it cannot be partially released beyond the preset shunt . A train cannot therefore be re-routed by cancelling the preset route and resetting for another route.    

Read Full Article