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Posted 97 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 

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Esat Kepenekli -
Posted 82 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

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Deepu Dharmarajan -
Posted 252 days Ago

ASPECT SEQUENCES

Signalling

  CONTENTS 1. Introduction 2. Plain Line Sequence 3. Diverging Junctions 4. Converging Junctions 5. Transition between Aspect Sequences 6. Isolated 4-aspect Signals 1. INTRODUCTION   Control tables contain details of the aspects displayed by each signal and the conditions under which they are displayed. To simplify testing, it is common to show the conditions for which each signal displays each of its aspects on a single document. As the final testing of signal aspects requires several persons to observe the aspects of a succession of signals the aspect sequence chart or table is of great assistance to the person coordinating the testing of aspect sequences. The aspects of shunting and subsidiary signals are not shown as they convey no information regarding the aspect of the signal ahead or the distance for which the line is clear. The text of these notes will refer to both British and SRA aspects. 2. PLAIN LINE SEQUENCE For any signal showing a stop or danger aspect,  there will be one or more aspects preceding it, warning of the need to stop. The aspect sequence information should already have been shown on the control tables. It can, if necessary be derived independently according to the following simple rules. Measure back full service braking distance from each signal at stop. The next signal outside this distance (still measuring back) will display the first caution to be seen by the driver. If there are no other signals between, this will be a caution (British single yellow) aspect. If there is one signal between, this will show caution and the signal outside braking distance will show preliminary caution/medium. British practice does not permit repeated cautionary aspects of any type but, for SRA signalling, if there are two or more signals between the first signal outside braking distance and the signal displaying stop, the medium aspect will be repeated as necessary and a caution aspect will precede the stop. Move forward to the next signal and repeat the process. When the aspect sequence is complete, a full set of aspects should be written down for each signal. To establish the conditions for a particular aspect to be displayed (e.g. when testing) the line from that aspect should be followed forward to its conclusion to show the aspects of signals in advance. Where low speed and/or conditional caution (warning) aspects are required, the aspect sequence should distinguish between the two by reference to the different overlaps and/or the clearance conditions required. The diagrams on the following page show the normal two, three and four aspect sequences. Examples of conditional caution, low speed and repeated medium aspects are also shown. NORMAL TWO ASPECT SEQUENCE (SINGLE LIGHT) NORMAL 3 ASPECT SEQUENCE (SINGLE LIGHT) NORMAL 4 ASPECT SEQUENCE (DOUBLE LIGHT) NORMAL 4 ASPECT SEQUENCE (BRITISH PRACTICE) CONDITIONAL CAUTION AND LOW SPEED ASPECTS REPEATED MEDIUM ASPECTS (CLOSELY SPACED SIGNALS) 3. DIVERGING JUNCTlONS Depending on the type of signalling, indication of a route diverging from the main line must be given at the junction signal and may also need to be given at the previous signal or signals. A separate line of the aspect sequence will be required from the signal at which the aspect sequence for the diverging (turnout) route differs from the plain line sequence. British practice requires approach control where a significant speed reduction is required. This should be noted on the aspect sequence chart. SRA does not use approach control for junction signalling so the aspect sequence is correspondingly simplified. If a junction signal is showing a proceed aspect for the turnout, the previous signal will display medium. It is recommended that the braking distances are checked to ensure that the required speed reduction can be achieved before the turnout. If not, two options are available; the medium aspect could be repeated or the aspect sequence leading up to the junction signal should be the same as that for the signal at stop. It should be noted that normal SRA practice normally requires the use of the medium aspect for junction signalling even where it is not used for the through route. The accompanying diagrams show the aspect sequences for a junction signal on lines signalled with three and four aspect signals for the main line. The aspect displayed by the junction signal should refer where  necessary to any turnout. route or junction indicator displayed as this will need to be checked when testing the aspect sequence. JUNCTION SIGNALLING (4 ASPECT - DOUBLE LIGHT) JUNCTION SIGNALLING (3 ASPECT - SINGLE LIGHT)   4. CONVERGING JUNCTIONS Because all trains at converging junctions must make the same speed reduction, and the driver is expected to know this, no special provisions are necessary for converging junctions. The sequences will combine at the first signal beyond the junction. 3 ASPECT SEQUENCE AT CONVERGING JUNCTION (SINGLE LIGHT) 5. TRANSITlON BETWEEN ASPECT SEQUENCES The transition between different aspect sequences sometimes causes difficulties, for example when running from a 3 aspect line to a 4 aspect line. The engineer must decide exactly where the transition occurs. This should of course have been considered at the time the signalling plan was produced to be able to decide the possible aspects displayed by each signal. The simplest rule to ensure getting the aspect sequence correct is to start from the stop aspect and work back. There should be no caution aspects further back than the first signal at or beyond braking distance. Where a 3 aspect line leads on to a 4 aspect line at a junction, the only reason for carrying the 4 aspect sequence back on to the 3 aspect line is if the signal spacing is inadequate for 3 aspect over the junction or the first section past (taking into account any speed restriction over the junction). Only use a medium aspect if it is necessary to obtain adequate braking (or to warn if a turnout ahead) not simply because· the signal is capable of displaying a medium. With SRA practice, the aspect sequences through diverging junctions will be similar, regardless of whether plain line aspect sequences are 3 or 4 aspect. In British practice, the aspect sequence should be maintained through the junction (together with any route or junction indicators) according to the aspects used on the diverging route. A junction signal reading on to a 3 aspect line will usually only display yellow (caution) or green (clear) for the turnout. 3 ASPECT TO 4 ASPECT TRANSITlON (SINGLE LIGHT) 4 ASPECT TO 3 ASPECT TRANSITION (SINGLE LIGHT) 6. ISOLATED 4 ASPECT SIGNALS At certain locations (approaching stations for example) it may be necessary to position two signals closer than braking distance in what is otherwise a 3 aspect sequence. The remainingsignals are all at least braking distance apart. In the example shown, there is insufficient braking distance from 105 to 107. Note that 103, the signal before the section shorter than braking distance is the 4 aspect signal. Note also that when 107 changes  from stop to caution, 105 and 103  will both  change  to a clear aspect together. ISOLATED 4 ASPECT SIGNAL (SINGLE LIGHT)      

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Deepu Dharmarajan -
Posted 258 days Ago

BASIC SIGNALLING PRINCIPLES | PART 1

Signalling

SIGNALLING BOOK | CHAPTER 2 | PART 1 CONTENTS 1. Introduction - In Part 1 2. Signal Aspects - In Part 1 3. Signalling Principles - In Part 2 4. Drawing Standards - In Part 2 5. Interlocking Principles - In Part 2 6. Train Detection & Track Circuit Block - In Part 2 7. Colour Light Signals - In Part 2 8. Control Panels & Other Methods of Operation - In Part 2 9. Colour Light Signalling Controls - In Part 2   1. INTRODUCTION Whatever type of signalling system is provided on a railway, its basic functions will remain the same. Safety must be ensured by preventing trains colliding with each other and locking points over which the train is to pass. The means of achieving these functions may vary from one railway administration to another but a set of rules must be laid down to define:- The positioning of signals The types of signals The aspects to be displayed by the signals and the instructions to be conveyed  by those aspects The controls to be applied to the signals The method of controlling points The method of interlocking points with signals The standardisation of human interfaces Many countries have sytems of signalling based on British railway signalling practice. The basic British system is very simple having only a small number of different signal aspects displayed to the driver. The driver is responsible for knowing the route over which he is to pass. The signal engineer must, in turn, provide sufficient information for the driver to safely control the speed of his train and, where necessary, to inform him which route he is to take. Other signalling systems have developed along a different path. The driver is given specific instructions to travel up to or reduce to an indicated speed. Route indications are optional. This will generally require a more complex set of signal aspects. This section will deal mainly with the principles and practices of the State Rail Authority of New South Wales, with reference to other systems where appropriate. 2. SIGNAL ASPECTS There are three principal types of signal, each serving a different purpose:- Main or Running signals control the normal movement of passenger and freight trains on running lines. The great majority of movements will be controlled by main signals. Subsidiary signals, mounted on the same post or structure as running signals, control movements other than for normal running, such as the shunting or coupling of trains. Independent shunting signals, generally similar to the subsidiary signals above, are provided for shunting movements at positions where there is no need for a running signal. We will examine the aspects displayed by each type of signal and the instructions and/or information conveyed by them. 2.1 Main or Running Signals As all early signals were semaphore signals, displaying a light for night time use, the aspects of colour light signals are usually based on the indications of the semaphore signals which they replaced. As most new signalling installations are likely to employ colour light signals, this section will concentrate on colour light signalling only. SRA (Currentlly TfNSW) employs two methods of signalling on main lines; single light and double light. As the name suggests, double light signals will always display at least two lights to the driver. Double light signalling is generally used in the Sydney metropolitan area. Single light signals normally use only one light to convey instructions to the driver, although a second marker light may be illuminated to aid the driver in locating the signal. Single light signalling is mostly used on lines outside the Sydney metropolitan area. Although there are similarities between the two systems, we will deal with each separately. We will then make a comparison with the corresponding aspects displayed by the British system to enable readers to read signalling plans drawn in British style. 2.1.1 Double Light Signalling This is intended for use in areas where signals are closely spaced. Each stop signal is therefore required to carry a distant signal for the signal ahead. To give the driver a consistent indications, each signal carries two separate signal heads. The upper signal head can be considered as the stop signal. It will always be capable of displaying, at least, stop and proceed aspects. The lower signal head can be considered as the distant for the next signal ahead. An additional green light may be provided below the distant. This is used for a "low speed" indication . FIGURE 1 shows the normal running aspects for double light signalling. Four aspects are used for normal running :- STOP is denoted by two red lights, one above the other. Note that the lower signal head will always display a red if  the upper signal is at red, even if the signal ahead is showing a proceed aspect. This is important to avoid misleading or confusing the driver. CAUTION is denoted by green over red. In other words, this signal is at "proceed" (top signal head) but the next signal is at "stop" (bottom signal head acts as distant). The caution indication tells the driver to be prepared to stop at the next signal. MEDIUM is a preliminary warning of the need to stop. It is denoted by green over yellow. Signals in urban areas may be closely spaced.  The one  signal  section between the caution and the stop may provide insufficient braking distance for a train travelling at full line speed. The medium indication tells the driver that the next  signal is at caution. This implies that he may have to  stop  at  the  second  signal ahead. CLEAR allows the train to proceed at maximum speed. A clear indication is two green lights. This will tell the driver that there is no need to reduce speed (other than for fixed speed restrictions) before the next signal. All the above indications require the driver to know where the next signal is, to safely control the speed of his train and be able to stop where required. An additional indication is provided on some signal, A  LOW  SPEED  indication, consisting of a small green light below a normal stop aspect tells the driver to proceed at no more than 27km/h towards the next signal. This is generally more  restrictive than the  caution. The low speed aspect is used when the track is only clear for a very short distance beyond the next signal. Fig 1: DOUBLE LIGHT SIGNALLING - ASPECTS FOR NORMAL RUNNING *Where a low speed indication is provided. Fig 2: DOUBLE LIGHT SIGNALLING - TURNOUT ASPECTS NOTE: A full clear indication is not given for turnouts. Note the difference in the indications given by Multi-light signals at a turnout. The yellow over red indicates "Proceed" at Medium speed through Turnout, next signal at "Stop". The Yellow over Yellow indicates "Proceed at Medium speed through Turnout" the lower Yellow is cautioning the driver to continue at Medium Speed towards the next signal which is indicating either "CAUTION" or "CLEAR" *Where a low speed indication is provided. **In the Sydney and Strathfield resignaled areas this indication represents a 'low speed' with  the train stop at stop. In this case the signal in the rear will show a caution indication. Figure 2 shows the indications for double light turnout movements. If there is more than one route from a main signal, the driver  must be told whether he is to take the main line or through route or whether he is to take a lower speed diverging turnout. This information is necessary to prevent the driver running through a turnout at too high a speed. The upper signal head is used to display a distinct proceed aspect for a turnout. Instead of the green normally displayed, a yellow light will tell the driver that he is to take the turnout. The proceed aspects for turnouts are:- CAUTION TURNOUT (yellow over red, also described in some operating documents as medium caution) tells the driver to expect the next signal to be at red. MEDIUM TURNOUT (yellow over yellow) tells the driver that the  next  signal ahead is displaying a proceed aspect. This is the least restrictive aspect for a turnout. There is no equivalent of a clear aspect for trains signalled over a turnout. To give a clearer indication to the driver where several routes are possible from one signal, the main signal aspect may be used instead, in  conjunction with a theatre route indicator. The route indicator contains a matrix of small  lunar  white lights which  can  be illuminated to display a Jetter or number. Each character will be associated with a distinct route. The route indicator is not illuminated when the signal is at stop.  When  the  signal  is required. to clear, the route indicator will illuminate for the appropriate route. LOW SPEED aspects may be used. If  a  low  speed  aspect is provided for a turnout route, this is no different in appearance to a  low speed for the main line route. This is not a problem as this aspect conveys a specific speed instruction. As the speed is  likely to be lower than that of most turnouts, route information is not essential 2.1.2 Single Light Signalling On lines where single light signalling is installed, the spacing of signals may vary widely. Therefore some signals may be combined stop and distant signals (as for double  light) but there may also be signals which are stop signals only or distant signals only. The instruction to the driver is therefore generally conveyed by a single light. A second marker light is provided below the main light to aid the driver in locating the signal. The meaning of the signal aspects is equivalent to the double light aspects but the appearance to the driver is different. FIGURE 3 shows the normal running aspects  for single  light signalling. The appearance of each aspect is as follows:- STOP consists of a red light. The marker light also displays a red, except on some older signals where it is lunar white. CAUTION consists of a single steady yellow light. The marker light is extinguished, except on some older signals where it is lunar white. If the main light should fail the marker light  will  display a red on stop signals or yellow on distant signals. MEDIUM, where this aspect is necessary, will be a flashing or pulsating yellow light. The marker light will operate as for the caution aspect. CLEAR is a green light. The marker light will operate as for the caution aspect. LOW SPEED aspects may be used in single light signalling where required. An additional small green light is provided below the marker light. The complete low speed aspect will be a main red light over a red marker light with the additional green light illuminated . Fig 3: SINGLE LIGHT SIGNALLING - ASPECTS FOR NORMAL RUNNING   Fig 4: SINGLE LIGHT SIGNALLING - TURNOUT ASPECTS The indication displayed by a Home signal for a turnout movement through facing points into a Loop Refuge siding or important siding consists of a band of three yellow lights in a subsidiary light unit (inclined towards the direction  of the movement). The Red light is  displayed in the Main line signal , as shown. The marker light for the main line signal, contained in the subsiduary light unit will be extinguished when the main line or turnout signal indication is displayed. 4.1 ROUTE INDICATIONS MAIN LINE At locations where more than one turnout is provided one signal indication is some times given and in such cases a route indicator working in conjunction with th e signal is provided, this enables drivers to ascertain the route for which th e signal has been cleared. The route indicator will not show any indication when the signal is at stop, but when the points have been set for the turnout movement a yellow light will appear in the signal in conjunction with the route indication showing a letter to denote the line to which the train will travel, e.g. Figure 4 shows the indications for single light turnout movements. For junction signals, two distinct methods are used according to the situation. For a simple turnout into a loop or siding, a separate turnout signal is provided below the main aspect, incorporating the marker light. For a CAUTION TURNOUT aspect, the main aspect remains at red, the marker light is extinguished and the three yellow lights of the turnout signal are illuminated . The row of lights is inclined in the direction of the turnout. For a MEDIUM TURNOUT aspect, the turnout signal will flash. Otherwise the appearance is the same as above. As for double light signalling, a theatre route indicator may be used in conjunction with the main signal aspect, where several routes are possible from one signal. Again the route indicator is not illuminated when the signal is at stop. When  the signal  is required to clear, the route indicator will illuminate for the appropriate route. The normal construction of signals is to provide a separate lamp unit for each light to be displayed . Some signals, however, are of the "searchlight" type. In this type of signal, the lamp is continuously illuminated and coloured lenses are moved in front of the  lamp according to the aspect to be displayed. The lenses are moved by a relay mechanism inside the signal head. The lights visible to the driver are the same for either type of signal. 2.2 Subsidiary Signals Associated with Main Signals As well as normal running movements, signals may be required for some of  the following movements:- Entering an occupied section Shunting into a siding Running on to a line used for traffic in the opposite direction. Attaching or detaching vehicles or locomotives. The main types are described below. As for the running signals, only current practice is covered in detail. Although the SRA (TfNSW) practice will allow subsidiary signals to clear immediately the route is set, many railway administrations employ approach control to delay clearance of the subsidiary signal until the train has come at or almost to  a  stand  at  the  signal. This  is usually achieved by timed track circuit occupation. The driver will receive a caution at the previous signal and will be preparing to stop. Subsidiary signals are short range signals which are only visible within a short distance of the signal. 2.2.1 Subsidiary Shunt and Calling-on Signals These authorise a driver to pass a main signal at stop for shunting purposes or to enter an occupied section. The driver must be prepared  to  stop short of  any  train or other obstruction on the line ahead. He must therefore control the speed of his train so that he can stop within the distance he can see. The appearance of these signals is a small yellow light below the main aspect. On  some older double light signals the letters "CO" in a round lens illuminated in white may be used. 2.2.2 Shunt Ahead Signal This signal is generally found on single and double lines worked under absolute block conditions. It permits the movement of a train past the starting signal for shunting purposes. It does not require a block release from the signal box ahead and the movement  will  eventually come back behind the starting signal when shunting is complete. As this method of working is generally only found outside the suburban area, a shunt ahead signal will normally be provided on single light signals only. It consists of a small flashing yellow signal below the main running signal and marker light. 2.2.3 Close-up Signal This is similar in appearance and application to the low speed signal. 2.2.4 Dead-end Signal This is for entering short dead end sidings directly from a running line. The only difference between this and a subsidiary shunting or calling-on signal is that the dead end signal is offset from the post on the same side as the siding leads off the main line. Subsidiary signals display no aspect when not in  use.  The  associated  main  signal  will  remain at stop when the subsidiary signal is in use. Route indicators may be used in conjunction with subsidiary aspects to give an  indication to the driver where multiple routes are available. In the case of a movement on to another running line in the wrong direction (i.e. opposite to normal direction of traffic) a route indication is always provided. 2.4 Shunting Signals Signals may also be required for shunting movements in positions where no main signal is necessary. The most common locations are:- Entrance to and exit from sidings. At crossovers to allow a wrong road movement to regain the right line. In yards and depots where main signals are not required. As they have no associated main signal, they must display a stop as well as a proceed aspect. 2.5 Dwarf and Position-light Signals Two main types are in use, the dwarf signal, with all lights arranged vertically and the position light signal. The diagrams show the various signal profiles.  Both types display two red lights for stop. The proceed aspect is normally only a yellow indicating caution. Shunting signals do not always prove track circuits clear and the driver must be ready to stop if there is another train occupying the section ahead. The proceed aspect may be accompanied by a route indication. Shunting signals are normally mounted at ground level, although they may be elevated if required for sighting. 2.3.2 Stop Boards If a wrong road movement is authorised from a shunting or subsidiary signal there must be another signal ahead to limit the wrong road movement. If no such signal was provided, the movement could continue past the protecting signal for the normal direction of traffic and cause a collision. The usual signal is an illuminated notice board carrying the words "SHUNTING  LIMIT". It can be considered as a shunting signal permanently at danger. 2.3.3 Facing Shunt Signals A shunting signal is sometimes needed in a position where it is passed in the normal direction by running movements. To avoid confusing  the driver by displaying a yellow light for a movement which may well be running under the authority of clear signals, these facing shunt signals are provided with an additional green light (clear aspect) for use only in this situation. 2.3.4 Point Indicators Although not signals in the same way as those just described, point indicators are important in sidings to avoid derailments and damage to equipment. They provide a visible indication of the position of hand operated points. Operation may be either mechanical or electrical. Located alongside the point switches, they display an illuminated arrow in the direction of the line for which the points are set. 2.5 British Signalling Aspects For the benefit of those who may at some time have to read signalling plans drawn to British standards (e.g. for the IRSE examination), this is a brief summary of the aspects in use, their meanings and how they are drawn. 2.5.1 Main Signals As with SRA (Currently TfNSW) practice, three colours are used, red,  yellow  and  green.  On  the  plan,  a  red light is denoted by a circle with a horizontal line across it. A yellow  light  has the line at 45° and a green light has a vertical line. The  "normaJ"  aspect  of  the signaJ  (i.e. with  no  routes set and all track circuits clear) is shown by a double line in the appropriate light(s). There are four available aspects; STOP is a red light, CAUTION is a single yellow light, PRELIMINARY CAUTION is two yellow lights and  CLEAR  is  green.The stop, caution and clear signals have the same meanings as the corresponding SRA  aspects. The preliminary caution is similar to the MEDIUM indication  of  SRA  signaJs. The  double yellow aspect is only used in situations where signals  must  be  positioned  closer  together than braking distance. Many lines use red, single yellow and green only. Marker lights are not used. There is no equivalent of the LOW  SPEED  signal. An equivalent control (to allow trains to close up provided they are running  at very low speed)  is provided  by delayed clearance of the yellow aspect. The train must be almost stationary at the signal before the aspect will change from red to yellow. This is achieved by applying approach control with timed track circuit occupation. 2.5.2 Junction Signalling Where a signal has more than one route, a distinct route indication must be given for each  route, except that the highest speed or straight route  need  not have a route  indication.  This may take one of two forms, a junction indicator (a row of  five white lights)  normally  above the main signal and pointing in the direction of the divergence or a multi lamp or fibre optic route indicator displaying one or two characters. There are six available junction indicator positions. Positions 1, 2 and  3 (at 45°, 90" and 135° respectively) indicate diverging routes to the left. Positions 4, 5 and 6 provide equivalent indications to the right. Multi-lamp or fibre optic route indicators are restricted to routes with a speed of 40 mph (64 km/h) or less. Where necessary, clearance of the junction signal is delayed by occupation of the approach track circuit (timed if necessary) to enforce a speed  reduction.  This  is  because  the  driver may receive no warning at previous signals of the route set from the junction signal 2.5.3 Subsidiary Signals The standard subsidiary signal is a position light with two white lights at 45°. The proceed aspect is both lights illuminated. There is no stop aspect -  the  associated  main  signal remains at red. Route indicators are provided  where  necessary but are not obligatory -  if they are provided, route  indications  must  be displayed  for  all routes. The subsidiary signal is used for all shunting and calling on moves. This is a short range signal. An approaching train must be  brought  to a stand  before clearance of the subsidiary aspect. 2.5.4 Shunting Signals The position light shunting signal has two white lights and one red  light. The proceed  aspect is identical to the subsidiary signal. The stop aspect is one red and one white  light, horizontally placed. The white light at the lower right {the "pivot" light) therefore remains continuously lit. A shunting signal with two red lights only is used as a "limit of shunt" indicator. 2.6    Summary Whatever the system of signalling, the signal engineer  must  have  a  detailed  knowledge  of the aspects displayed to the driver and the instructions conveyed. He must then design  the layout of the signalling and the associated controls so that the driver can safely obey all signal aspects. This  must apply for all types of  train likely to use a line. When  required  to reduce  speed or stop, trains must have adequate braking distance under all conditions. The driver of a train must never be given an instruction by a signal that he is unable to comply with.   TO BE CONTINUED - SIGNALLING BOOK | CHAPTER 2 | PART 2...........

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Deepu Dharmarajan -
Posted 72 days Ago

BASIC SIGNALLING PRINCIPLES | PART 2

Signalling

CONTINUED FROM - SIGNALLING BOOK | CHAPTER 2 | PART 1 SIGNALLING BOOK | CHAPTER 2 | PART 2 CONTENTS 1. Introduction - In Part 1 2. Signal Aspects - In Part 1 3. Signalling Principles - In Part 2 4. Drawing Standards - In Part 2 5. Interlocking Principles - In Part 2 6. Train Detection & Track Circuit Block - In Part 2 7. Colour Light Signals - In Part 2 8. Control Panels & Other Methods of Operation - In Part 2 9. Colour Light Signalling Controls - In Part 2   3. SIGNALLING PRINCIPLES   Any railway administration must have a set of rules which determine the basic principles of design and operation of the signalling system. In some cases they may be carefully documented in detail, in others they may have developed through many years of custom and practice. At the very minimum, the operating rules must define the meaning of each signal aspect. British Rail has a set of Standard Signalling Principles. They will not be referred to directly in this course but many of the BR principles are similar to SRA (TfNSW) practices. 4. DRAWING STANDARDS Most readers will be involved in the design, specification, installation, testing or maintenance of signalling equipment. They will inevitably have to convey  large amounts of technical information to others. This is usually done by means of drawings. It is important to appreciate the impact of drawings on engineering activities. They are used to:- Specify a signalling system Agree the specification with the users (operating department etc.) Agree the specification with suppliers/contractors Estimate costs Order materials Construct and install equipment Test an installation for correct operation Maintain the equipment Locate and rectify faults The information included in the drawing will vary considerably according to which of  the above purposes it will serve. A drawing will generally need  to be read  by someone  other  than  the person  who  produced it. In the same way that persons talking to each other need to speak the same language, engineers need to use common conventions and symbols in their drawings to convey the necessary information. If a drawing is not understood, it is of no practical use. SRA (TfNSW) have developed a large range of standard schematic and circuit symbols to depict signalling equipment and electrical circuits. A copy of these symbols is provided with these notes. Also provided are the main schematic symbols likely to be used on British signalling plans. These are incorporated in a British Standard -  BS  376.  As this has not been revised for a number of years, certain additional symbols not included in BS376  are now in regular use. In most cases, each railway administration will have its own company standards for the production of technical drawings. It is nevertheless important that the signal engineer should be able to ensure that each drawing is responsible for issuing, conveys the necessary information. This may include the use of symbols and terminology peculiar to the signal engineering profession or even to a particular company. 5. INTERLOCKING PRINCIPLES To understand some of the basic principles of interlocking, it is best to start by referring to a simple mechanical signalbox. Most Readers will not be engaged in the installation of mechanical equipment, but many mechanical signalboxes still exists and it provides a simple example which demonstrates the general principles. Each lever in the frame has a normal and a reverse position. For signals, the normal position is always associated with the danger or stop aspect.  Moving the lever to the reverse position operates the signal to the proceed aspect. With points, normal and reverse have similar status, each being associated with one of the two possible positions of the points. However, the normal position is generally used to set points for main routes. This terminology has been carried forward to electrical signalling although levers are no longer used. lt is therefore essential to remember the association between the terms normal and reverse and the state of the equipment. In the mechanical signalbox depicted below, the levers are mechanically interlocked. A signal lever cannot be moved from normal to reverse  unless all point levers are in the correct position. Once the signal lever is reversed, the point levers for that  route  and  any which provide additional protection, cannot  be moved from  their current position (normal or reverse). Signal levers reading over the same  portion of route in opposite directions cannot be reversed at the same time. Starting signals 3 & 7 when operated will not lock any other lever. They will however be electrically controlled by the block equipment to the adjacent signal boxes. Home signal 2 requires points 5 normal. Conversely, 5 points reverse will lock  signal 2 in the normal position. Signal 2 need  not directly lock signal 4 as the signals  require 5 points in opposite positions. To reverse 4 signal lever requires 5 points reverse AND 6 signal normal. To reverse distant signal lever 1 requires signals 2 AND 3 reverse. In colour light signalling practice there is no equivalent to this type of interlocking as distant signals will usually work automatically, controlled by the aspects of the stop signals ahead. It should be evident from the above examples that all basic interlocking is reciprocal (ie. if 4 reverse locks 6 normal then 6 reverse must lock 4 normal, if 5 is required reverse to release 4 then 4 in the reverse position will lock 5 in the reverse position). The reciprocal nature of locking is inherent in the construction of any mechanical system but in electrical systems the engineer must ensure that it is provided. It is a useful  check to ensure that for each basic interlocking control the converse is also specified. It is possible to produce a complete set of interlocking controls (the  locking  table). However, as modern signalling systems do not employ lever frames, the format shown is no longer used. As its main purpose is to specify the construction of the mechanical interlocking, the converse of the releases is not shown, neither is the locking applicable for moving the lever from reverse to normal. Although adequate for this purpose, it is totally inadequate for an electrical system. RELEASED BY (Req Lever Reverse)   LEVER NUMBER LOCKS (Req Lever Normal) 2.3 1     2 5   3   5 4 6   5 2.8 5 6 4   7     8 5 7.8 9    release the lever in the left hand column, the other levers must be in the position shown.   REQUIRES LEVERS LEVER NUMBER N -> R R ->N 1 2R.3R   2 5N 1N 3   1N 4 5R.6N   5 2N.8N 4N.6N 6 4N.5R   7   9N 8 5N 9N 9 7R.8R   6. TRAIN DETECTION & TRACK CIRCUIT BLOCK The development of a safe, reliable means of detecting trains, the track-circuit, allowed a major advance in safety and ease of operation. The earliest application of track circuits was to prevent a signalman forgetting a  train standing at his home signal, and giving permission for another train to enter the section. To do this, the berth track circuit bolds the block instrument at "train on line". The use of track circuits was then extended to cover sections of line which were out of sight of the signalman, and also to lock facing points while trains were passing over them. It was soon realised that a track-circuit could be used to ensure that the whole of the section was clear. There would then be no need for signalmen to supervise the entry and exit of trains, to ensure the section was clear. "Track-Circuit Block" was thus created and block instruments could be dispensed with. With track-circuit block, the rear signalman does not have to ask permission to send a train forward, be can do so whenever the track circuits are clear up to the end of the overlap. 7. COLOUR LIGHT SIGNALS The development of track-circuit block made it possible for signals on plain line to work automatically - a signal could  show clear when the section track circuit was clear, and stop if otherwise. Normally, no action would be necessary by the signalman, other  than  to observe that the trains were running normally. This, in turn, made it economic to have short block sections, allowing increased line capacity, as a signalbox was no longer needed for each block section. The use of automatic colour light signals soon became widespread. The signal aspects were  and still are as described in section 2. Usually the appearance of  the  signal  is  slightly modified to identify it  to the  driver  as an  automatic.  This may be by  means of  a sign or as in SRA (TfNSW) practice, by offsetting the  upper  signal  head to the left for double light  signals  and by offsetting the marker light towards the track for single light signals. The manner in which colour light signals are used will differ according to the required capacity of the line. 7.1.  2 Aspect Signalling This is a direct colour light replacement for the mechanical distant and stop signals. The block section is the length of track between two successive stop signals.  Each stop signal will have an associated distant signal at least braking distance from it. Block sections will generally be long, typically several times normal braking distance. 7.2.  3 Aspect Signalling To increase the frequency of trains on a line, the block sections must become shorter. When the length of the block section is not  significantly greater than normal braking distance, 3 Aspect signalling economises on the number of signal posts required by combining the two signals at the same position along the track. Each stop signal also displays the distant aspect for the next stop signal. Each signal can display stop, caution or clear. The length of the block section must always be greater than or equal to braking distance. 7.3.   4 Aspect Signalling On high speed lines or those with a high traffic density, it is often necessary to have block sections shorter than braking distance. It is then necessary to give  the  driver  an  earlier  caution indication, as he has insufficient distance to stop between seeing the caution and arriving at the stop signal. In such cases, the signal in rear of the caution shows a medium aspect as a Preliminary Caution. This is a "4 aspect" signalling system as each signal can display four distinct indications to the driver. Although, in theory, capacity could be increased further by the introduction of additional aspects, few railways have found it necessary to do so,  unless  associated  with  the introduction of automatic train control. It is  likely  that  too many  different  aspects  would lead to confusion. If the total length of two adjacent block sections is less than braking distance due to signal positioning requirements, it would appear that a further aspect is necessary. SRA (TfNSW) practice however is to repeat the medium caution in this situation. British practice is to ensure that signals are suitably spaced to avoid this situation. Note that the additional "low speed" aspect used on many SRA (TfNSW) signals is not for increasing headways at normal speed. Although  it often forms  part of  the normal sequence of aspects to bring a train to a stand, its overlap generally coincides with  the caution aspect and does not affect the overall line capacity. Its purpose is to allow trains to close up to each other after their speed  has been safely  reduced. It is particularly useful in the vicinity of stations to minimise the effects of station stops on line capacity, although its inclusion in the normal aspect sequence can be restrictive if a full overlap beyond  the signal at stop is available. This will be covered in more detail in later sections. The existence of low-speed aspects does not need to be taken into account  in determining the capacity of a line for through running at normal line  speeds, unless  the  low speed overlap lies beyond the caution overlap for the signal in the rear. 8. CONTROL PANELS & OTHER METHODS OF OPERATION The introduction of colour-light signals, and power-operated points, in tum allowed the bulky and cumbersome lever-frame to be replaced by modem signalboxes with panels. The standard British type of panel has for many years been the "Entrance-Exit" (N-X) type, with push-buttons for setting routes. Each button has 3 positions: middle, pushed and pulled. The button is sprung to return to the middle position after it is either pushed or pulled. To set a route and clear a signal, the entrance  button  corresponding  to that signal  must  first be pushed and released. This  button  will flash,  to indicate  it is the selected  entrance.  Toe next button pressed is taken to be  the exit or  destination.  Provided  the  route  between  the two buttons is both valid and available, then the route will  set,  the  entrance  button  will change to a steady white light, and in addition white route lights will illuminate to the destination. With the route set, any points will move to the required position automatically.  Provided the route is clear, the signal will then clear. To restore the signal to red, and release the route, the entrance button is pulled. If required, the points can be controlled manually from the panel. Each set  of  points  is provided with a three position switch for this purpose.  With  the  switch  in  the  central position, the points will move automatically as  routes are set.  Alternatively,  it  may  be turned either left to move the points normal, or right to move them reverse. The position of all trains in the panel box area is indicated by red track circuit lights on the panel, normally appearing in the same aperture as the route lights. Indications are also provided for each signal, and each set of points. Unlike a lever frame, where the signalman can only pull a lever if it is safe to operate that signal or set of points, with a push-button panel the signalman is always able to operate the buttons or switches - but the trackside equipment will only respond provided it is safe to do so at that time. The "interlocking" is used to ensure this safety. Conventionally, the interlocking has been done with relay circuits, a typical panel signalbox requiring many thousands of relays. Relay technology, although very reliable in operation, is now being replaced on many railways by electronic or processor based systems. British Rail, in conjunction with Westinghouse and GEC, have developed "Solid State Interlocking" (S.S.I.), which is now being used in a large number of installations, achieving significant savings in space and cost. SSI also has the advantage that alterations to the signalling controls do not require extensive alterations to physical wiring. Most of the controls are stored as data which can be prepared off-site beforehand. Improvements in technology have not only revolutionised the interlocking equipment. Attention has also been given to the interface with the signalman. Although S.S.I. may be operated from a conventional control panel, it is becoming more usual to use video display units (VDU's). These can either be used as a direct replacement for the control panel or as part of a much larger integrated system for providing all train running information to signalmen, passengers and other operating staff.   As an example, the BR IECC (Integrated Electronic Control Centre) includes a train describer system, automatic route setting to a stored timetable, train reporting, passenger information systems, communication with adjacent signal boxes and extensive monitoring facilities. If all trains are running normally, the signalman can sit back and watch the trains go by while the Automatic Route Setting does most of the work. SECTION OF A TYPICAL CONTROL PANEL (BR Style) 9. COLOUR LIGHT SIGNALLING CONTROLS   This section describes the normal controls which would be found on a modem colour light signalled layout operated from a control panel. 9.1. Types of Route A ROUTE is the section of track between one signal and the next.  All  routes  have  an entrance and an exit. A signal may have more  than one route if  there  are  facing  points ahead of it. Although the exit is usually another signal, it may be a buffer stop (terminal platform or siding) or an unsignalled portion of the railway (depots,  yards or  sidings).  A route is uniquely defined by the number of the entrance  signal,  a suffix  defining  the direction of the route (in order from left to right as seen by the driver - normally a letter although some railways use numbers) and,  where  necessary,  a letter denoting  the class of the route. The type of the route is determined by the purpose of the train movement. In  British terminology these are known as classes of route. Each class of route will  have different controls applied. SRA (TfNSW) does  not  use  the term class; however,  there are  three general types of route (four in British practice). A signal may have more than one type of route to the same exit. 9.1.1 Main Routes A main route is from one main running signal to the next. The signal proves all track circuits clear and points correctly set and locked up to the next signal, which is proved alight. In addition, a further distance beyond the exit signal is also proved clear with points set. This is known as an "OVERLAP". The purpose of the overlap and the determination of its length will depend on the type of railway, the setvice operated and the provision of any protective devices to prevent a train running past a signal at danger. In the Sydney metropolitan area, trainstops are provided which are set to operate a tripcock on the train's braking system if a signal  is passed at danger or in some cases approached at too high a speed. In this case the length of  the overlap should be sufficient for a train which bas been tripped to stop within the overlap. Overlaps distances may therefore vary for each signal according to line speed and gradients. Under present day operating conditions,  the worst case overlap  would  be of  the order  of  830 metres for a line speed of 115 km/h on a  1 in 50 (2%) down gradient. Overlaps may often be longer than the signal sections. Elsewhere, trainstops are not provided. Unless and until some form of automatic train protection is provided, there is no certain means of ensuring that a driver will not inadvertently pass a signal at danger. The driver bas the final responsibility for obeying the signals. So, whatever the length of overlap, there is no guarantee that it will be adequate for all situations. It can therefore be considered as a margin for error if the driver misjudges his braking or the train braking system does not perform adequately. A nominal 500 metres is the present standard. This has been shown by experience to be adequate for most situations. In special circumstances, the overlap distance may be reduced. The end of the overlap is indicated on signalling plans, and often on the signalman's panel. Routes giving a low speed aspect may also be classified as main routes although the overlap will be much shorter (often 100 metres or less). Some caution or low speed aspects may be conditionally cleared (i.e. approach controlled) to permit a shorter overlap to be used at the next signal. In British practice such routes would be defined as "warning" routes. SRA (TfNSW) does not make such a distinction. 9.1.2. Calling-on Routes Some railways prefer a separate type of route for passenger trains running into occupied sections (e.g. bringing a second train into a partially occupied platform. This is known as a calling-on route and will require a distinct aspect, the main aspect remaining at stop or danger. Although calling-on signals exist on SRA (TfNSW), there is now no distinction between calling-on and shunting routes. Calling-on moves will be made under the authority of a subsidiary shunt signal (see 9.1.3.). 9.1.3. Shunt Routes A shunt route is used for low speed (usually  non-passenger)  movements,  e.g. into or out of sidings or for shunting between running lines. Any move into a line which is not proved clear, e.g. a siding, and any move from or up to another shunt signal or "limit of shunt" is classed as a shunt move. Shunt routes may be from dwarf or position light shunt signals or from a main signal, using a subsidiary signal on the same post. Route indications are provided where required. For a shunt route, the signal proves all points correctly set and locked. Proving of track circuits will depend on the policy of the railway concerned and local operating requirements. If it is regularly required to shunt into an occupied line, track controls should not be provided. Some sidings, of course, may not even be track circuited. Where a shunt move is made using the subsidiary aspect of a main signal, the train should first come to a stand. This can be partially achieved by using only a short range signal. However, some railways require the subsidiary signal to be approach controlled by timed track circuit occupation. For a shunt move from a ground-shunt signal there is no requirement for approach control, although it is sometimes provided. The train should either be approaching at low speed anyway or it will have set back behind the signal and must first stop before reversing direction. Where propelling moves (i.e. with the driver at the rear of the train) are regularly made past a shunt signal, some railways employ "I.AST WHEEL" replacement of the signal aspect so that the signal does not go back to danger until the driver has passed the signal. In such cases the signal continues to show a proceed aspect,·even, when the train occupies the first tracks beyond the signal, and is only replaced when its berth track clears. 9.2. Approach Locking  When a route is set, the interlocking will lock all the points in the correct position, and lock out any conflicting and opposing routes. The signalman must not be allowed to restore the route, and release this locking, with a train approaching the signal. This is called "APPROACH LOCKING". Once a signal has cleared, its route cannot be released until either:- the train is proved to have passed the signal a suitable time delay has elapsed, allowing an approaching train to see the replaced signal (or any cautionary aspects leading up to it) and be brought safely to a stand without any risk of passing the signal at danger. there is proved to be no train approaching ("Comprehensive Approach Locking") Proving that the train has  passed  the signal  is done by monitoring  the sequential  operation of the track circuits immediately beyond the signal. 9.3 Point Controls Although the signalman has a switch for manual control of each set of points, they are normally controlled automatically by the setting  of routes. The points are  then  locked  by the route set over them. The points are also locked by the track circuits over them, so that they cannot be moved under a train. Where a set of points has more than one end, then they are locked by the tracks over all ends. If a track circuit adjacent to the points is positioned so that a train standing on one of the diverging tracks could be foul of a movement over the other track  (a "foul" track circuit) it must be proved clear before the points are allowed to move to the position which would allow the fouled movement. 9.4. Route Locking Once a train has passed a signal, its route can be restored but any points, conflicting routes, etc. ahead of the train must remain locked. This is done by the "route locking", which is indicated by the line of white lights on the signalman's panel. The release of  route locking must first be preceded by the release of approach locking (i.e. it is safe to start releasing the route. If the route is cancelled after the train enters the route, the white lights extinguish behind, releasing the points for other moves. The white  lights always remain alight in front of the train, holding the points ahead locked. If there is no train in the route at the time of release and the approach locking has proved that there is no train approaching or it is safely at a stand, the whole of the route  will release immediately.

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Deepu Dharmarajan -
Posted 250 days Ago

CABLES

Signalling

CONTENTS 1. Introduction 2. Signalling Cables 3. Telecommunication Cables 4. Power Cables 5. Selection of  Cable Type 6. Methods of Termination 7. Cable Routes 8. Cable Construction 9. Cable Jointing 10. Cable Testing 11. Fibre Optic 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.     SIGNALLING CABLES   Most lineside signalling circuits are d.c. or mains frequency a.c. Voltages are low, typically 24 - 130 volts.   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 construct ion 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:-   Internal wiring   This is usually flexible (stranded conductor) for easy installation along relay racks 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) is often preferred now as it generally satisfies fire regulations.   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).                  Lineside Cables   " Although these may carry simil 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 subjected to changes in temperature and humidity, often  lying  in  waterlogged  ground. Often oil and vermin will 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.   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.                    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.  B.R.  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.     2.           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 neighbouring circuit, commonly called "Crosstalk". The degree of crosstalk which may be encountered can depend on a number of different factors e.g.   The frequency of the disturbing signal i.e. crosstalk increases with frequency (square waveforms, because of their high harmonic content are particularly troubl esome).   The magnitude of the current flowing in the  disturbing    i.e.  crosstalk increases with the current.   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.     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. SELECTION OF CABLE TYPE   Lineside Signalling Circ'!ii§ _ ..., . ,.., ·· 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 0.6 to 2.5mm 2 To economise on installation costs, a smaller number of cables with a higher number of cores is preferred.   Preferred sizes for B.R. multicore cables are 10, 12, 19, 27, 37, and 48 cores. Conductor sizes are either 110.85mm or 111.53mm.   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 : 1 core Track cables 2 core Track cables 4 core Clamp locks 7 core Colour light signals 10 core Color light signals/point machines 12 core Colour light signals/point machines 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.   Remote Control Systems and SSI Data Links   In the context of railway signalling, the  term  remote  control  has a specific  meaning.  It  is  the transmission of a large number of non-vital control and indication circuits  between  a control centre and an interlocking.  If  the system  should  fail  in  any  way,  the interlocking will still ensure the safety of train operation.   In some areas, a vital remote control link replaces the line circuits from the interlocking to track-side equipment. The system is then designed such that failures will not cause false operation of points or signals. SSI employs a fail-safe data link between the interlocking and trackside equipment. ol are available; direct wire, FDM and TOM.   With  direct  wire  a single  cable  core  (1-,,,1;  ,•.  :::::,1,1,   .,  "  :·t11TT1)    !''r  pair  is allocated  for  each function.  Telecommunications  cable  can  be  used.  A  special  , ,.:: •r, r.~1_,; ;;:.  w le  with  a  large central return conductor has also been employed. With the reduction in cost of dectronic equipment, TDM can now be economic over very short distances (and can also be traction immune) . Direct wire is unlikely to be the first choice for a new installation.   Both FDM and TDM systems employ a.c. signals. For FDM circuits normal signalling multicore cables can be used with some limitations. A twisted pair cable of similar construction to signalling cables is available specifically for FDM systems and is where possible the preferred choice. This reduces crosstalk betw_een systems.   TDM systems generally employ telecommunications type cable. As they require only a few cable pairs (typically 2 or 4 per system including standby) it is not economic to provide dedicated cable and the signalling TDM systems will be carried over the telecomms network. This is acceptable for safety as TDM is generally a non-vital system.   SSI data links employ a single twisted pair cable to convey the a.c. signals between interlockings and trackside modules.   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.                    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.     2.            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.   Toe following are the most widely used forms of termination :-  

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Deepu Dharmarajan -
Posted 210 days Ago

CHECKING PROCEDURES

Signalling

CONTENTS 1. The Purpose of Checking 2. What Should be Checked? 3. The Checking Process 4. Checking for a Typical Signalling Project 1. THE PURPOSE OF CHECKING 1.1 The Signalling Production Line  The following is a very simplified view of a signalling project from beginning to end. Note that checking does not appear as a specific item. This is because it should be built into each stage to ensure that it is being carried out correctly. This is part of the quality control of the whole project. It should be an integral part of every task. Each check should be recorded so that the next stage can use the results of the previous stage as a basis from which to work. 1.2 The Importance of Checking A signalling system is required to perform correctly to ensure the safety of the railway. Unfortunately the system is specified, designed installed and tested by humans. Humans despite their ability to process information better than any computer have a tendency to make mistakes occasionally. The purpose of checking is to ensure that these mistakes are detected and corrected before they are incorporated into a working system. 1.3 Checking Principles These notes cannot cover in detail how to check. That is a skill which the checker develops with experience. There are however some basic principles which should be observed. The producer should first check the work. Any responsible designer should not pass on his work knowing that there are errors present or assuming that another person will find any deficiencies. The designer should aim to get  his work right frrst time. Of course this will not always be possible but, if errors have been made, it is better for the producer to identify them for his own future reference. All formal checks should be independent.  Anybody,  particularly an  engineer can become so familiar with his work that he fails to detect simple  and obvious mistakes. Where checking is a mandatory part of any design process, this should be performed by somebody who has not been involved in the detail of the work. Be sure of your assumptions. Any drawing will make certain assumptions, about site information, equipment performance, materials or the user of a system. The checker should ensure that he is informed of all assumptions made and be prepared to challenge them if necessary. Record all checks as you go. If you get interrupted, it is possible to see where you need to resume. If somebody takes over from you, he will know what is left to be done. Most important, you have a record for future reference that the check has been carried out. Be sure you check enough. On a new installation, deciding what to check is  easy - everything is a new design so it all needs checking. Where alterations to working circuits are involved, this decision is not so easy. For a minor  alteration, there is no point in checking every circuit on every wiring diagram if 95% of them are unaltered.  However, deciding the boundaries of what should be checked requires great care. 2. WHAT SHOULD BE-CHECKED? These notes are mainly intended for those who will be involved in producing and checking drawings in various forms. These drawings will be used for:- Agreeing the specification for the system. Estimating and ordering of materials A contract with a supplier or installer Installation of the equipment Testing and commisioning Maintenance of the system, probably for a long period after it has been installed. Drawings retained as a record of a working system will be used as the starting point for any future alterations. It is just as important that these are correct as those drawings used for installation. Drawings used for any of  the  above functions, either directly or indirectly,  should always be independently checked. The checking should ensure that the drawings are consistent with all previously checked drawings for the same project or system. 3. THE CHECKING PROCESS  3.1 Who Should Check?  As mentioned earlier, the first check should be performed by the producer himself. In most cases this will be followed by a more formal check which should be independent of the producer. Many organisations have strict rules as to who should check certain types of  work, or the work of specific individuals. These notes do not set out to challenge those rules. If there are no clear rules on checking in your organisation, it would be desirable to establish some. The general principles must be that the checker will:- Be independent of the work which has been done. Nobody should be required to certify that their own work is totally correct. In general, though, it is acceptable for a person who is involved in the planning or management of a project to check elements of the detail provided he has not been involved in the production. Be qualified to check the work in question. He should obviously be capable of doing equivalent work himself. It is a matter for each organisation to decide whether and how to ensure, certify, and record  that an individual is capable of checking particular types of work. Have the authority, either directly or indirectly, to ensure that any errors found are corrected. Many organisations require that the checker is of equivalent or higher status than the producer. These principles can be applied whether persons are employed purely as  checkers or alternate between production and checking. 3.2 When Should Checking Be Done? In general, checking should be an integral part of each step in a project.  It should ideally be done as soon as possible after completion of one stage and  before the commencement of the next. Otherwise there is a risk of errors  being carried forward which will subsequently be more difficult to correct. Only in the case of very minor works should checking of the whole design  process be attempted in a single stage. 3.3 Where Should Checking Be Done? Most design work will be done in an office and there is no reason why the checking should not also be done in the same office. However, some checks  will require information from site. If these are not adequately documented in the office, a physical check of certain site details may be necessary. 4. CHECKING FOR A TYPICAL SIGNALLING PROJECT  As an example of the type of checks that should be made to ensure the accuracy of all documentation for a signalling project, the main types of drawings required for a new or altered route relay interlocking are listed below  together with the type of checks that should be made and the source of information against which the check can be made. It is important to note that this is not an exhaustive list. The student will no doubt think of other items to add. It should also be noted that many of the checks involve ensuring consistency between drawings. Others may require reference to external sources  of information. 4.1 Signalling Plan/Layout Check Source of Information Track layout correct Distances accurate Braking distances adequate Signal profiles correct Route information correct Track circuits correct Signal/point/T.C. numbering Headways adequate P.Way drawings, site surveys P.Way drawings, site surveys Braking charts/tables, gradient profiles Signalling principles Signalling principles Signalling principles Signalling principles Headway charts  4.2 Control Tables Check Source of Information All signals & points listed All controls included Converse controls shown Signalling plan Signalling principles,signalling plan Cross-check between control tables 4.3 Location Area Plan This is normally derived by adding information to a copy of the signalling plan. It should therefore be confirmed that the original signalling plan has been checked. Check Source of Information Each function (signals, points, track feeds and relays assigned to a location Location suitably sited By examination of plan Site survey 4.4 Interlocking Wiring Diagrams Some work can be saved here if the circuits have been drawn to standard masters, with only the individual function numbers/letters added to each sheet. Provided the master has been checked for correct circuit operation, only the existence of the correct circuits and the correct labelling need be checked. Check Source of Information All circuits drawn All controls included Correct circuit operation Equipment space allocated Relay contacts allocated Correct contact type used Fuses allocated Terminals allocated Wire count recorded Signalling principles, circuit knowledge, control tables Signalling plan, control tables Circuit knowledge Relay rack layout Relay contact analysis Contact analysis, relay specs Busbar allocation Terminal panel Relay contact analysis 4.5 Cable Schematic Check Source of Information All locations included Correct size & type of cables Location area plan Cable core allocation, power supplies 4.6 Cable Core Allocation Chart Check Source of Information All functions included Correct type of circuit Through spares reserved Circuit suitable for cable type Signalling plan, location area plan Signalling principles, loc & relay room  wiring By observation Knowledge of equipment 4.7 Location Wiring Diagrams (& Equipment Layout) Check Source of Information Equipment space allocated All functions included Terminations correct Circuits correct Loc. internal layout drawing Location area plan, cable core allocation Cable core allocation Signalling  principles 4.8 Track Circuit Bonding Plan Check Source of Information Position of block joints Clearance points Traction bonding continuity Min/max T.C. lengths Series bonding Feeds/relays shown Signalling plan, P.Way drawings Control tables By observation Signalling principles By observation Location area plan 4.9 Control Panel Faceplate Check Source of Information Correct layout Numbering Indications Button & switch types Track circuit colours Signalling plan Signalling plan Signalling principles Signalling principles By observation 4.10 Relay Rack Layout Check Source of Information All relays shown Relays correct type Wiring diagrams Signalling principles, relay specs 4.11 Terminal Panel Check Source of Information Circuits shown Functions allocated Wiring diagrams Cable core allocation 4.12 Power Supplies Check Source of Information All supplies shown Transformers etc. correct rating Fuse discrimination Fuse/busbar allocation Wiring diagrams Wiring diagrams (equipment count) Wiring diagrams Wiring diagrams 4.13 Relay Contact Analysis Check Source of Information All relays shown Correct contact arrangement Wire count shown Contacts allocated Relay rack layout Relay specs Wiring diagrams Wiring diagrams 4.14 Aspect Sequence Chart Check Source of Information All sequences shown All sequences correct Signalling plan Signalling plan, control tables 4.15 Other documents Other documents not included here may comprise:- Remote control schematics Remote control allocations & interfaces Level crossing layouts Train describer stepping controls Train describer interfaces On computer based systems such as SSI and most train describer systems, much of the information is computer generated data. Checking and testing SSI installations is a large enough topic for a course on its own. It is too specialised to be covered in detail here.  

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Sotto -
Posted 91 days Ago

Custom HVAC Control Panel for Sleeping Car Compartments

Rollingstock

Around 100 control panels with integrated compartment control technology including all validations - in just 9 months from the drawing board to delivery with a strong partner. We offer # project management, # standards management, # hardware design, # software design, # mechanical design, # product design, # procurement, # assembly and testing  all from a single source! Together with our QM-validated supplier base, we realize your project. Feel free to talk to me!

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Jyoti TV -
Posted 26 days Ago

Fixed Block Vs Moving Block

Signalling

  Significant developments are made to railway signalling from Fixed block era to Moving Block, Communication based Train Control System . The below comparison table shows some of the major differences between conventional fixed block systems and moving blocks and the advantages. No. Fixed Block (Absolute Block ) Moving Block 1 Trains are defined per fixed block and only one train in a block at a time. That is protected train routes in a fixed block Trains are considered as moving blocks and distance between trains is maintained at safe distance.   2 In a three aspect fixed block conventional signalling minimum distance between following train with proceed authority  towards preceding train  is twice the maximum braking distance for the worst-case rollingstock operating in the line plus safety margin provided by overlap beyond a stop signal In a moving block system minimum distance between the following train with proceed authority  towards the preceding train  is just the braking distance needed for the following train plus a safety margin required by the CBTC system 3 Position of limit of authority is restricted to see a Signal (By driver) visible continuously for 3 seconds Position of limit of authority don’t have such restriction. 4 Even if fixed block signalling system is protected with ATP system, the train has to pass over a transponder to receive a new limit of authority , until train sees a transponder it travels with restricted speed set by the previous transponder Limited authority is continuously updated as there is continuous two way communication between onboard and trackside ATC equipment.   5 High level of operational variability and driver to driver run time variation  can cause delays , affect performance ATO can enable  continuous , consistent automated driving profile and thereby eliminate driver run time variance 6 Large quantity of track side equipment to be maintained, including signals  Trackside signals are used for train recovery during complete ATC non availability thereby eliminate the requirement for Signals 7 If additionally protected with ATP(Automatic Train Protection) , will ensure trains don’t SPAD (Signal Passed at Danger) by automatic enforcement of Movement Authority limit and Automatic enforcement of speed limit Note : If Manual Trainstops or AWS are implemented it's still degraded compared to ATP Maintain two-way radio communication with each train on the network, monitoring train position with onboard equipment and thereby ensuring safe train separation by sending limit of Movement Authority (MA) to each train on the network. It also enforces this limit with overspeed protection 8 Train detection equipments such as Track Circuits , axle counters are mandatory to ensure the fixed block is free before sending a train Train detection is based on onboard equipment,and secondary train detection systems such as Axle counters or track circuits are ‘not necessary ‘ unless degraded modes of operation needed 9 More number of Wayside equipment such as Signals are required Uses  onboard VDU (Video Display Unit ) Note:Signals might be used for secondary signalling or degraded mode of operation or train recovery during complete failure of ATC(Automatic Train Control)  system 10 Pedestrian crossing and level crossings are allowed as the headway (Headway is the distance between vehicles in a transit system measured in time or space. The minimum headway is the shortest such distance or time achievable by a system without a reduction in the speed of vehicles) are relatively high Pedestrian Crossing and Level crossing are ‘possible’  to integrate with CBTC , however the whole purpose of headway reduction will be impacted and are not commonly implemented. In nutshell  both are contradictory requirements (Arguably ) Note: No provider has successfully implemented a level crossing with a CBTC system for heavy traffic road users 11 Less capacity , safety,reliability, serviceability, and resilience High  capacity,safety ,reliability,serviceability, and resilience 12 Schedule optimisation is limited possibility Schedule optimisation possible after a disruption  with faster recovery 13 Real time Passenger information cannot be accurate Precise Passenger Information Possible and can predict the exact time of arrival 14 No coasting ability to conserve  Coasting or other alternate strategy to conserve energy.

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Deepu Dharmarajan -
Posted 253 days Ago

HEADWAYS

Signalling

Coming Soon.......

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Contact . -
Posted 97 days Ago

Innovative PantoSystem Prevents Service Disruptions to Paris RER Network of RATP

Automatic Train Supervision

      The customer RATP is a state-owned public transport operator and the biggest transport company in Paris with 60,000 people responsible for engineering, exploitation, and maintenance. The company provides multiple transport modes such as metros, buses, trams, and regional express rail (RER) network. RATP has a total of 28 lines of metro, trams, and RER in the Parisian metropolis.   The challenges/problems Within a two-week interval, incidents related to the spring box of two separate pantographs running on opposite train tracks, were identified. In one of the incidents, the abnormal wear of the carbon strip kept deteriorating, and when the carbon strip finally had a pitch angle between -3,8° and -3,4°, the PantoSystem generated a level 1 alarm in one of RATP´s RER networks, indicating a warning of high importance. After examining the 3D images of the pantograph, the PantoInspect team urgently sent an e-mail to warn RATP about the carbon strip, which had clearly been bended. Immediately after, the exploitation team of RATP took the train off the track and when the problem was investigated by the maintenance team, they confirmed that the horn of the pantograph was hit by an unknown object, causing the spring box to twist on one side.   The solution As the PantoSystem has not yet been validated by formal tests, the RATP does not yet have a dedicated team to handle the train alarms and take appropriate action, and that is why, they were very pleased to receive a direct warning from PantoInspect, that a train required attention. The company was also very satisfied that the PantoSystem enabled them to detect the consequences of the twisted or broken spring box, by accurately measuring the geometry of the pantograph. The automatic system is important due to the fact that RATP has about 90 km of tracks on each direction, a total of 180 km track on both directions, and since this type of problem does not happen frequently, manually identifying this type of defect throughout the RATP fleet would have been very time-consuming and costly for RATP as it is not visible from the ground. Additionally, to manually investigate if more trains were affected would again require a major effort.                Figure 3: Broken spring box             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 9120

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Deepu Dharmarajan -
Posted 212 days Ago

INTERFERENCE & IMMUNISATION

Signalling

CONTENTS Introduction Traction Systems D.C. Traction Systems Mixed Traction Systems Protection Against Other Forms of Interference Future Developments and Problems 1. INTRODUCTION Electric traction is increasingly being used as an economic means of operating a railway. Electric power is taken from the national or regional supplier. Due to the scale of production this can normally be produced at a lower price than with individual power units on each locomotive. Electric locomotives are much simpler and cheaper to control maintain and operate than their diesel equivalent. Electric traction brings with it a number of additional problems for the signal engineer. Signalling equipment, in most cases, operates at relatively low voltages and currents compared to locomotives and multiple units. Unavoidably, traction circuits run alongside and even share conductors with signalling circuits. Interference, usually through direct contact or induction must be anticipated and equipment protected from its effects. Even without electric traction, signalling equipment may still be subject to interference from adjacent power supply lines or lightning storms. Similar techniques are often employed to protect against the likely effects. The objectives of protection (or immunisation) can be summarised as:- Prevention of failures, particularly wrong-side failures. To ensure the safety of staff working on the equipment under normal operating conditions and, as far as possible, under traction fault conditions also. To prevent the effects of traction currents from damaging or destroying signalling equipment. 1.1 Electrification Systems The effects of electric traction and the precautions which must be taken will depend on the type of traction supply. The electrification system chosen for a railway will, in tum, depend on a number  of factors:- Type and frequency of traffic Availability of Power Supplies and the locations at which they can conveniently be brought to the lineside. Local geographical and climatic conditions Structural clearances (for overhead wires etc) The overall length of the line Whether the line to be electrified is an extension to an existing electrified line or a completely new traction system. As a result many different systems are in use. Once a system has been selected, it is very expensive to change due to the investment in traction units and power supplies. The systems can generally be divided into two groups:- A.C. systems, normally employing a high voltage (typically 25kV) with overhead current collection. D.C. systems, generally at much lower voltages (600 to 1500 volts). The method of current collection is either overhead (requiring a much heavier conductor than for a.c.) or third rail. Low voltage systems tend to be d.c. because this makes the traction equipment on the trains much simpler. Early electrification did not have the benefits of modern power semiconductors to control traction motors so the power was at a voltage which could be applied directly to the d.c. traction motors. The cost penalty is a large number of substations and heavy feeder cables. The use of a.c. traction permitted substations to be spaced considerably wider apart and the overhead conductor to be used as the main feeder. No separate feeder cable is necessary. The equipment on board the train is generally more complex. The high supply voltage must be transformed to a usable voltage and rectified to d.c. for the traction motors. Modern variable frequency a.c. drives have now made the induction motor a viable alternative to the series wound d.c. motor. 1.2 Modes of Interference In most cases one or both running rails are used for the return current path. To some extent earth currents will also be present. In all types of track circuits there is the risk of interference by direct contact, traction currents passing through the signalling equipment or between the signalling equipment and earth. There is a high risk that traction currents could cause wrong side failures. The incidence of right side failures could affect reliability to an unacceptable level. Other circuits are generally not in direct contact but there is still the possibility of induced interference. lrtsulation could also break down causing direct contact with the traction supply. Protection must also be provided against dangerously high voltages (either induced or through direct contact) which could injure or kill personnel working on signalling and communications equipment. 2. A.C. TRACTION SYSTEMS 2.1 Feeder Arrangements BR's 25KV 50 Hz AC. traction system is typical of those on many other  railways and is usually derived from the132 KV National Grid system. The  supplies are taken as single phase through 132/25 Kv transformers provided by the Supplier. The supplies are taken to feeder stations at usually the same phase. Adjacent feeder stations are not parallel (i.e. not necessarily from the same  phase and usually not from the same source. This enables the Electricity  Authority to balance the railway load between the 3 phases of its system. The distance between feeder stations is dependant on traffic and power requirements.  An electric locomotive accelerating with a full load may take  a  current of the order of 270 amps. Neutral sections are provided between feeder  stations to separate the supplies and track sectioning cabins (TSC) are located at  intermediate points and the boundaries of feeding sections to provide alternative feeding and track isolation facilities in the event of failures or isolation for maintenance. 2.2 Return Paths for Traction Current 2.2.1 Rail Return This is the simplest form of traction current return. In most cases, only  one running rail is used. On plain track this is normally the cess rail, but in complex  layouts the location of return rail changes in order to meet track circuit  requirements by cross-bonding. The problem with rail return is that the rail is not well insulated and return traction current will leak to earth over the  length  of  the return rail. This produces a large imbalance between the current in the overhead wire and that in the rail, which  dramatically increases the level of induced voltages in lineside cables (see later sections for details). 2.2.2 Return Conductor If the traction return path is well insulated, the current imbalance in the circuit is reduced, hence interference is minimised. A return conductor can therefore be provided to carry the traction return current. The current carried is in anti-phase to the current in the contact and catenary wires, and similar in magnitude,  therefore the net electro-magnetic inducing field is reduced. The reduction over rail return, where signalling  curcuits are placed in the optimum position for minimum interference, is of the order of 45%. 2.2.3 Booster Transformers Some of  the return current will still flow via earth instead of the return wire.  This will be in inverse proportion to their relative impedances between the train and  the substation. The cost of a conductor large enough to eliminate the earth currents would be prohibitive. To force the majority of  the return current into the return conductor, transformers are provided in the traction circuit as shown on the following page. Typical Arrangement of Booster Transformers The return conductors are bonded to the traction return rail midway between booster transformers. These are located at 2 miles, 3.2 Km intervals, the primary winding connected in series with the catenary and the secondary winding in series with the return conductor. The effect of the booster transformer is to produce a current in the return conductor which approximates to that in the catenary, but is 180- out of phase. Maximum suppression of induction is achieved with the traction load at the mid-point connector (95% reduction) and the minimum when at the booster transformers. This alone does not immunise signalling and communications circuits. As the two conductors are widely separated, induction will still occur whenever a signalling circuit is nearer to one conductor than the other. The relative positioning of the overhead conductors, the return conductor and the signalling cable route must be such as to place the cable route equidistant from the traction conductors. 2.3 Modes of Interference and Immunisation Techniques Of the three possible modes of interference, conduction, electrostatic induction and electromagnetic induction, induction is the dominant mode in a.c. traction areas. Conduction, by direct contact between the power line catenary and the rails,  equipment or cable conductors happens rarely. If unprotected, it is usually  fatal to personnel and equipment. The only safeguard is the provision of contact circuit breakers in the traction supply. Due to bonding of overhead structures direct to the traction return rail, the risk of  a traction fault raising the rail potential, and that of track circuit equipment,  to dangerous levels is small. Track circuits will however be subject to false operation due to the multiple return paths created by return conductors and earth bonding and extra precautions must be taken when setting up and adjusting track circuits to ensure safe operation. Due to the distance between the traction equipment and the signalling  equipment and the low supply frequency of 50Hz., electrostatic effect are usually negligible. Electromagnetic induction is caused in one conductor by current flowing in another. This action is similar to a transformer, the traction conductors being the primary winding and the signalling conductors the secondary. The voltage is induced along the conductor (not between the conductor and earth). The effect is maximised when conductors run parallel to each other. The induced voltage increases with length of conductor and decreases with separation of the conductors. As signal engineers we are concerned with the following aspects of a.c. induction into our lineside cables: AC. voltages produced under normal operating conditions that could  affect  line circuits and tail cable circuits and result in the malfunction, failure or damage to equipment and/or hazard to staff working on the equipment. Higher levels of voltage induced in our cables as a result of traction  system faults. Any increase of these effects due to disconnection, earthing  or other failures  within the signalling Dangerous levels of induced voltage are possible if the traction current rises rapidly (short circuit or traction flash over). Telecommunications circuits are susceptible to all normal levels of induced voltage on unprotected cables from the traction system. Therefore special measures have to be adopted to protect these systems from the 50 Hz base and odd harmonics of this frequency. 2.3.1 Positioning of Cable Route The simplest method to reduce the levels of induced voltage is the physical location of the cable route, as described earlier. The best position for the cable route is approximately equidistant from the two traction conductors (where booster  transformers and return conductors are provided). With the normal  B.R.  overhead line equipment, this is 9 ft (2.75m) from the centre of the nearest track, and 2 ft (0.61m) below running rail. This distance will obviously vary for different designs of overhead equipment, for multiple track lines where two or more return conductors are mounted together, and for lines without booster transformers and/or return conductors. On most circuits which form a loop (one conductor out and the other return), this provides an adequate level of protection for normal operation provided the signalling equipment is in full working order. Both conductors are subject to the same electromagnetic fields which tend to oppose each other. Under fault conditions (earth faults and/or disconnections) further protection will be required. 2.3.2 Electro-Magnetic Screening With any wire installed parallel to an A.C. electrified line, a reduction in interference is obtained by the screening effect of earthed conductors in its vicinity. This includes cable sheaths, metal pipes and running rails. All communications cables are provided with a screening sheath (usually  aluminium)  with up to a maximum of 4 steel tapes around the sheath.  These  are connected to a good earth of no more than 4 ohms located every 1000 m. Signalling cables run in the same cable routes as screened telecomms cable and  therefore benefit from the mutual screening effect between the cables. Where existing cables, not to electrification standards are to be retained, it may be possible to immunise them by a separate screening conductor. This is a large cross-section copper wire run along the length of the cable route and earthed as above. Cable sheaths should also be earthed. 2.3.3 Immunisation of Relays Relays for d.c. circuits can be designed to withstand substantial a.c. voltages without energisation. The relays have copper slugs fitted over the cores, near the pole pieces and  a magnetic shunt is fitted between the cores above the copper slugs. When a DC voltage is applied to the winding the DC flux is produced as normal and attracts the armature. Some of this flux is diverted via the magnetic shunt and therefore greater power has to be supplied. However, when an AC voltage is applied, the AC voltage has difficulty in establishing itself across the air gap due to the large copper slugs and it tends to short circuit the air gap via the magnetic shunt, thus the AC flux plays little part in the operation of the mechanism. The following diagram shows the principle. A.C. Immune Relay Construction 2.3.4 Choice of Operating Frequency Where d.c. circuits are not practical, equipment should be designed to operate at frequencies other than the mains frequency and its harmonics. Filters can be used to keep signalling and traction currents separate Although the mains frequency is normally very accurate, fluctuations can  occur  and  these must be allowed for in the design of systems. Fluctuations of  ±  0.5%  are  typical  so  the design may allow for 1% maximum error to give a degree of margin for error. It should therefore be evident that the available bandwidth between successive harmonics decreases by 2Hz each time and above 1kHz no bandwidth  is  available.  In  practice, harmonics of this order are very small and frequencies  above 1.5 kHz are successfully  used  for track circuits. For additional safety, two or more frequencies are used together so that traction faults could not generate both together. 2.4 Practical Immunisation of Signalling Equipment 2.4.1 Limits Appreciable earth currents may still flow for some distance away from electrified lines and protection must be extended sufficiently far for their effects to  become  negligible.  At  the limits of electrification, or where  a  non-electrified  line  leaves  the  electrified  lines, experience has shown that signalling equipment should be immunised for 880 yards (800m) from the electrified line. 2.4.2 Line Circuits These should be DC circuits using AC immunised line relays. The length of line must be limited to 2km to ensure that the induced voltage from the traction system does not exceed limits for electrical safety (maximum induced voltage of 110v). Circuits required to cover greater distances must be repeated  by means of a relay and new power supply. Where circuits run along  non-electrified branches,  they  must be cut 800m from the electrified line. Where circuits from the same supply feed in opposite directions,  care  must  be  taken  to  ensure that the total length of parallel circuits is less than 2km. All vital line circuits are double cut to reduce possible false operation  and  hazard  to staff where an earth fault is present. 2.4.3 Track Circuits The traction return current can ususally be carried satisfactorily by only  one of  the running rails. Single rail DC track circuits, immune to the highest AC voltage that  could  occur, are used. It has been found desirable to limit the track circuit length to a lower value than on non-electrified lines to prevent the combined effect of a return conductor and a broken rail providing an alternative path to the train shunt. The track feed set must be designed  to  prevent  a significant  DC  voltage  being  applied  to the rails as a result of rectification of AC from  the  traction  current.  The  track  relay  must also be immune to AC in the same manner as those used for line circuits. Reed track circuits operate  at frequencies  clear  of  50Hz  harmonics  and  may  also be  used in AC electrified areas as may most modulated audio frequency track  circuits  such  as  the TI21. When little used and therefore rusty rails require  track  circuiting  there  are  two solutions - a welded stainless steel strip on the top surface of the rail or a high  voltage impulsing type of track circuit. The Jeumont  track  circuit  is immune  to false  operation  by AC traction current,  but  its length  is severely  limited  in a.c. traction  areas. This may  not be a serious disadvantage, as it is mostly used for point and crossings into sidings and loops. 2.4.4 Signals Colour light signals use tungsten filament lamps, which operate readily on both AC and DC. Therefore the only method of  preventing  induced  AC lighting  the lamp is to limit the length of the circuit between control relays and lamps and employ as high a voltage as practical. The usual practice is to have a transformer for each aspect in the signal head to reduce the voltage to the 12 volts or less required to operate the lamp and supply llOV AC over  the contacts of the controlling relays. In this  case  the  maximum  parallelism  allowed  is  200 yards (183m), i.e. a signal head  must  be less than  200 yards  from  its controlling  relays.  If the overall maximum distance between signals fed from the same location  or  relay  room supply exceeds 200 yards, then an isolating transformer  is required  to feed  signals  on  one side of the location or relay room. By limiting the length of signal lamp circuits, it is unnecessary for them to be double cut. Shunt signals generally operate on 110 volt lamps so no transformer is necessary. Searchlight signal operating mechanisms  must  be immune  to false operation.  This immunity is achieved by the use of chokes mounted as close as possible to, and in series with, the d.c. searchlight mechanism. An a.c. searchlight signal could be operated at a different frequency (e.g. 83.3Hz) 2.4.5 Points Electric point machines are immunised by using permanent magnet machines. These ensure that, even if there is an AC voltage at the terminals, the motor's field will  remain  uni-directional and although there will be considerable vibration, there is no resultant  torque and therefore the motor will not move. Electro-Pneumatic point machine valves must be immune. These valves are immunised  in a similar manner to that outlined for relays. Electro-Hydraulic (clamp lock) point mechanisms were found to have inherent immunity and can be used with no special measures being taken. Mechanical Points should  have  insulation  inserted  in the point  rodding  at the ends adjacent to the lever frame and  the  points.  This  is to prevent  stray  voltages  causing  electric  shock  to personnel. Detection of all types of points is by polarised relays. These relays are fully immunised in the manner already described. 2.4.6 Level Crossings Where lifting barriers are used it is desirable to position the barrier so that, if it is knocked over no part of it shall come closer than 150 mm to the overhead line equipment. If other positioning requirements make this impossible,  then  the  barriers should be made of metal or have a continuous metallic strip of adequate section along its length. The barrier or metallic strip should be bonded to a traction return rail or cable. Control circuits must be immunised as already described. Where closed circuit television is used special precautions must be incorporated  into the design. 2.4.7 Remote Control Immunisation of remote control systems is dealt with in the separate notes covering remote control. This mainly involves line isolation at regular intervals. 2.4.8 Power Supplies Although the safety precautions in force for higher voltage power supplies  would cater for the possibility of induced voltages at the levels expected, care must be taken when working on supplies which are switched off to avoid the possibility of high induced voltages. As the cable may not be sectionalised in the same way as vital signalling circuits, dangerous voltages could occur on long power feeders. 3. D.C. TRACTION SYSTEMS Because of the low traction voltage, traction currents are high, typically, 2,000  -  3,000 amps per train during acceleration. Due to the large DC return  currents  present in the earth near to and in the return rail, there are problems caused by corrosion, and problems  caused when insulation, equipment and cables break down. A d.c. supply will normally produce no inductive interference effects other  than from switching transients and ripple at harmonics of the mains frequency from  an  unsmoothed power supply. The main hazard is from conduction (to which track circuits are particularly exposed) by direct contact or via earth faults. The main precautions therefore comprise operation of equipment from a.c.  supplies, effective insulation arrangements and earth leakage detection. 3.1 Limits Earth currents from d.c. supplies are much more troublesome than for a.c.  They may propagate over much longer distances and immunisation should be provided for at least 3km from a d.c. electrified line. 3.2 Line Circuits DC circuits are used which are not sectionalised other than for volt drop purposes. It might initially seem unwise to. use d.c. but the reasons for accepting d.c. line circuits on B.R. in most situations are as follows:- All cables have non-metallic sheaths and are therefore less likely to pick up DC potentials along their routing. All cables are tested to a rigid specification. Additional insulation is provided by terminating cables on non-metallic materials. All line circuits are double cut to ensure that an earth fault in one leg of the circuit cannot cause false operation. Additional earth leakage detection equipment is used. In most d.c. traction supplies there is a significant a.c. ripple from the rectifiers.  Use of a.c. circuits would not provide immunity from the effects of this ripple  3.3 Track Circuits AC track circuits use vane relays which have self  immunity to the effects of  DC.  Even where the traction supply may contain a.c., the two element vane  relay will only operate if the interference signal is at the correct phase relationship. The relay will not respond to higher harmonics unless these are contained in the correct proportions in the supply to both coils. Reed and TI21 track circuits and several other audio frequency track circuits  are also immune to the effects of DC. 3.4 Signals No special precautions are taken for signal lighting circuits. These are usually a.c. fed with signal head transformers. Search-light signals are operated by a.c. vane type mechanisms, which, like track relays, have self immunity to DC. 3.5 Points No special precautions are taken in the choice  of machine for the control of  points. Although a.c. machines might be considered to have better immunity, d.c. operation is normally acceptable at higher voltages (110-130 volts) together with adequate earth leakage detection. Clamp locks, having separate valve and motor circuits can only be falsely operated by two simultaneous faults. Detection of points may be achieved with a.c. circuits using vane type three position relays. Alternatively, 110 volts a.c. may be used from the detector to the location where each individual circuit is transformed and rectified to operate a 50 volt d.c. line relay. 3.6 Automatic Warning System The BR Automatic Warning system, using d.c. magnetic fields is particularly  susceptible to d.c. traction effects. The train equipment is designed to detect the magnetic fields produced by the track equipment. Unfortunately, currents in the rails, on the traction unit itself, and in cross-track feeders can cause similar fields. This  problem  is overcome by:- Mounting the receiver away from collector shoes, traction equipment and associated cables and screening it on all sides except directly below. Use of track equipment which produces a higher magnetic field streangth. 4. MIXED TRACTION SYSTEMS There are some areas where both traction systems are in use, either using the same tracks or an adjacent track. This means that the signalling system has to be immune to both  AC and DC traction supplies. Circuits used must operate  on a  frequency distinct from the mains frequency and its harmonics. 4.1. Limits Although the d.c. immunity is required for a greater distance,  it is normal  to dual  immunise for approximately 3km. 4.2 Line Circuits Circuits are usually d.c. with precautions taken as for a.c. and d.c. lines. 4.3 Track Circuits Formerly, the most popular method was to use a.c.  two-position vane relays  but operated from an independent power supply at a frequency different to the mains supply and its harmonics (normally 83.3 Hz for 50 Hz mains). The additional power supplies were a significant added cost. Modern audio frequency track circuits such as the TI21 are immune to both d.c. and a.c. traction. 4.4 Signals The circuits are identical to those used in AC traction areas.  Searchlight  signals are immunised by using an AC vane type mechanism with a maximum length of 60 yards (55 metres) for the feed circuit. If signals are more than 60  yards  apart on either side of the relay room or location an isolating transformer must provided in the feed circuits of all signals on one side of the relay room/location. 4.5 Points The methods of operating points are identical to those used in areas of AC traction. Detection of all types of point is either by a two element vane relay from an  independent supply at a separate frequency, or by a filtered circuit such as the GEC vital Reed system. Frequencies 477.5 Hz and 414.75 Hz (fype RR  4000)  have  been  allocated for use with point detection circuits on B.R. and are employed for Normal and Reverse detection respectively. 5. PROTECTION AGAINST OTHER FORMS OF INTERFERENCE Apart from traction, adjacent power supplies and lightning are the main sources of electrical disturbance. Power transmission lines generate the same type of interference as  a.c.  traction and protection is therefore similar. Lightning protection is a very specialised area and will only be covered in outline. A direct lightning strike produces voltages far higher than the worst traction  fault conditions. It is virtually impossible to provide effective protection. When  lightning finds a path to earth, it will however raise the voltage at the point at which it enters the earth. Currents will flow which, although of extremely short duration, can induce large voltages in adjacent equipment. The danger is that the voltages may be large enough to find a path through the signalling equipment or break down insulations in cables etc. Fortunately, protection can be provided against this effect by the provision of  surge arrestors. The most common type is a gas discharge tube which has three electrodes, one connected to each leg of a loop circuit. and the other to earth. For the  normal  operating voltages of the signalling circuit, it will appear as an open circuit.  When the voltages induced by lightning are sufficiently high, an arc will form in the gas discharge tube which will provide a low impedance, high current capacity path to earth for the duration of the lightning strike. When the current is insufficient to sustain the arc,  the surge  arrester  will revert to its open circuit state. Semiconductor devices are also available to operate in a similar manner.  Their switching time is much faster than a gas discharge tube, giving quicker protection, but their current capacity is much lower. They provide better protection against moderate strikes but may not be able to handle the current caused by severe strikes. Both types of device are also suitable for protecting vulnerable equipment  (e.g.  electronic track circuits) from traction fault conditions where required. 6. FUTURE DEVELOPMENTS AND PROBLEMS We have concentrated so far on interference caused by the supply. This is always at the mains frequency or harmonics of it and these frequencies can therefore be filtered or avoided as appropriate to the type of equipment. Electric traction units have in the past invariably employed d.c. traction  motors. These do not produce any different interference to that already produced by the power supply. Many railways are now employing traction units either with d.c. motors  and  variable frequency thyristor chopper controllers or more recently, ac. variable frequency induction motors. The control equipment for these types of traction unit can produce interference at many (often continuously variable) frequencies over a broad spectrum. It is impossible to detail specific problems but the signal engineer must be very careful in the future as new traction units are introduced that he is aware of  their possible effects on the signalling equipment.

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