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Deepu Dharmarajan -
Posted 19 days Ago

Signalling Downstream Power Supply

Signalling

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

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Deepu Dharmarajan -
Posted 31 days Ago

Automatic Train Control (ATC)

Automatic Train Control

Automatic Train Control is the CBTC system which automatically controlling the train movement while enforcing safety. ATC provide command to motoring the train, coasting, braking, regulating the speed with accurate station stopping. This system automatically protects the train (ATP) while ensuring safe separation between trains and protection from over speeding. Refer Fig 1 for the functionality of Automatic Train Control. Through out this document “Trackside”  means equipemnt installed on track or along the geometry of the track , “Wayside”  Means  equipment associated with Signalling Equipment Room /Control Room and Trainborne means equipment installed on the train. Fig 1  Functionality of Automatic Train Control Based on Functional Elements, ATC has wayside equipment and Train borne equipment to perform this functionality. a)    Train Borne (Signalling)  Train-Borne Signalling Cabinet ( ATO , ATP ,TDM ) Radio Antennas Under Train Sensors (Balise Scanner) Tachometer Video Display Unit (VDU) b)  Train Borne (Train Supplier) Speedo Meter and Or Odometer Brake Relay Encoder Cabinet Train Integration Management Cabinet c)  Trackside        Balise DCS Access Point (AP) for Wifi d) Wayside DCS Equipment Cabinet Wayside Computers for ATP and ATO (Zone Controller ) Interlocking Subsystem Automatic Train Supervision Subsystem  Functionalilty of Element 1.1     Train-Borne Signalling Cabinet – Train Borne ATP System  Automatic Train Protection processing unit belong to the train borne computer system. This subsystem is in charge of the continuous control of the train speed according to the safety profile and applying the brake if it is necessary. It is also in charge of the communication with the wayside ATP subsystem in order to exchange the information needed for a safe operation sending speed and braking distance, and receiving the limit of movement authority for a safe operation. Refer Section 1.15 for wayside system details  1.2    Train-Borne Signalling Cabinet – Train Borne ATO System Automatic Train Operating Processing unit belong to the train borne computer system,  It is responsible for the automatic control of the traction and braking effort in order to keep the train under the threshold established by the ATP subsystem. Its main task is either to facilitate the driver or attendant functions, or even to operate the train in a fully automatic mode while maintaining the traffic regulation targets and passenger comfort. It also allows the selection of different automatic driving strategies to adapt the runtime or even reduce the power consumption. Refer section 1.14 for wayside ATO system details 1.3     Train-Borne Signalling Cabinet-TDM Train Data Management Processing System is providing the interfacing functionality with Trains Integrated Management. This is the processor-based System offer health monitoring, train event recording and control of train initialisation. It is also the interface for train door control, command train to wake up and sleep. Processor process the data received from various train borne subsystem and send to the ATS.  1.4 Radio Antennas  Antennas are generally installed on exterior roof of the train, part of the Data communication system Transmit and Receives (Bi -Directional ) processed data between Train-Borne  Radio Unit and Trackside Data Radio Unit . Refer Access Point section 1.12  & DCS 1.13 1.5 Under Train Sensors (Balise Antenna )  Part of Geographical Position (Location Reference ) functionality of a CBTC solution  ,train borne balise transmission module radiates energy wave  to activate the ground balise to uplink geographical position  transmission  and these sensors are mean  for collecting the spot transmission data . Spot transmission wayside devices (Fixed Balise) provide the train with information allowing the train to check and to calibrate its odometer, and to identify the actual train location. In general on CBTC solution  rest of the bi directional data transfer is  happening through radio. Refer  Balise section  1.11 1.6 Tachometer  This is the speed sensing device otherwise known as wheel impulse generators or speed probe .It can be opto isolator slotted or Hall Effect sensors .It detects the speed of the train and passes on to Train-Borne controllers(ATP and ATO)   and speed measured b Tachometer  is also used to ensure train at stand still before TDM inform TIM to open the door. Speed will be displayed on the speedometer 1.7   Video Display Unit (VDU)  Optional unit for GoA4 (Grade of Automation 4), however most of the CBTC has a VDU , accessible only when needed ,especially during  the degraded mode of Train Operation. Its kept covered in a box and accessible for Train Operator when needed.  GoA1 and GoA2 will necessarily have a unit displaying speed ,brake enforcement needs ,warning etc (Train Protection ,Train Control Information ) ,mode of operation  selector switch , driving ontrol handle  etc where as GoA4 VDU could be displaying equipment operating staus ,failure conditions rest are  defined based on operator needs. Refer Fig 2 for a ruggedized VDU designed per EN 50155 / EN50121-3-2 / EN61373.   Fig 2  Video Display Unit        1.8     Speedo Meter Unit which display of the speed of the train  1.9     Brake/ Relay Encoder   The Trainset unit automatically control the speed and regulate the speed based on the information received from  ATP and ATO processors. 1.10     Train Integration Management (TIM)   The system which interface between Signalling and Trainset  ,which provides health monitoring status to Train Data Management(TDM)  upon request .When ATS issue Train readiness command  via TDM  to TIM and ATC for their preparedeness for readiness .Train(TIM)  and ATC set ready and send the readiness status back to the  ATS via TDM .If readiness is not available a fault code will be send back to ATS .TIM use the clock along with TDM to ensure synchronisation.TIM also communicate with the Passenger Information System with the same “clock” 1.11     Balise  The Track Installed Transmission System performing a safe spot transmission, conveying safety related information between the track and the train. Information transmitted from an Up-link Balise to the On-board Transmission Equipment is fixed Spot transmission, when a transmission path exists between the wayside equipment and the On-board Transmission Equipment at discrete locations. The information is provided to the train only as the Antenna Unit passes or stands over the corresponding Balise. The length of track on which the information is passed is limited to approximately one meter per Balise.For CBTC application fixed balises are widely used to provide the train with information allowing the train to check and to calibrate its odometer, and to identify the actual train location. In nutshell in a  CBTC  solution  rest of the vital  bi directional data transfer is  happening through radio. Refer  Balise Antenna  section 1.5. 1.12 Access Point (AP) of the Data Communication System ( WiFi )  An access point is a wireless network device that acts as a portal for devices to connect between Wayside and Train borne Equipment installed along the Trackside. Access points are used for extending the wireless coverage of a wired DCS network so that the train passes by the area covered by an access point can establish seamless bidirectional data transfer. A high-speed Fibre Cable a Data Communication Cabinet with router from the equipment room to an access point, which transforms the wired signal into a wireless one. Refer Radio Antennas section 1.4 & Data Communication System 1.13 which work hand in hand. 1.13 Data Communication System (DCS )  The Communication network formed by redundant fibre optic cables based on geographical layout of the railway. This is making use of cable route diversity to ensure no single point failure Occurs. DCS network is normally formed in a ring topology so that any components fails availability is ensured by re routing the communication within the ring. Dual switches are provided at each location for the availability of the local area network. 1.14 Wayside Computers -Wayside ATO System. The system in charge of controlling the destination and regulation targets of every train. The wayside ATO functionality provides all the trains in the system with their destination as well as with other data such as the dwell time in the stations. Additionally, it may also perform auxiliary and non-safety related tasks including for instance alarm/event communication and management, or handling skip/hold station commands. Refer section 1.2 for Train borne ATO system details. 1.15  Wayside Computers -Wayside ATP System  This subsystem undertakes the management of all the communications with the trains in its area. Additionally, it calculates the limits of movement authority that every train must respect while operating in the mentioned area. This task is therefore critical for the operation safety. There are bidirectional communication established between wayside and Train borne ATP system Refer section 1.1 for Train Borne ATP system. 1.16 Interlocking system   The system  which control the wayside equipment such as point machine ,signals (for fall back mode) , and gathers the secondary train detection system such as track circuits /axle counters (train recovery ) for locking the wayside equipment in front of a running train .Depends on utilisation of  the non-core functionality of  CBTC trackside equipment vary .Interlocking will become master during degraded mode ,during a complete ATO failure ,for recovering the train ,again depends on operator definition. 1.17 Automatic Train Supervision System (ATS)  The system responsible for controlling and monitoring the unmanned train operation according to time table or headway .There is another article detailing Automatic Train Supervision in RailFactor . Feel free to refer to that for more details . Architecture of  ATC (CBTC )  Refer Fig 3 for System Architecture of an Automatic Train Control System(Distributed)    Fig 3  CBTC System Architecture ATC constitute of the complete subsystem as shown in the figure 3. It varies from supplier to supplier. Some of them have centralized architecture, and some have distributed architecture. In the figure 3, above shows a distributed architecture. For the explanation purpose consider .Three (3)   trains stabilized in the depot  are  to be operated with  3 min headway.  2.     CBTC Operation   For the sake of explanation, Automatic Operation (Un manned Train Operation) has been taken into consideration and degraded mode of operation or manual route setting ,or operator intervention sequence are not included .Sequence of  route call will be same as automatic ,only difference  is  that these process of route call is made manual from control centre ,or back up control centre or station control centre. 2.1.     Role of ATS Primary objective of Automatic train Supervision is to control and monitor the train operation and manage the train operation according to timetable or specific headway. Trains stabilized in the depot has a profile that can be uniquely identified by the ATS for tracking. ATS maintain a record of each train consist profile with a train identification. Note : The train identification is a static field uniquely sourced from train supplier  with physical car numbers ,ATC number of the train. Refer section 1 .17 and another Article Automatic Train Supervision in RailFactor  2.2.     Role of ATC (ATO/ATP/TDM)  ATC receive the wake up command from ATS through the DCS network transmitted to the  trackside via Access point  .Train antenna mounted on roof of the train captures this signal and pass on to the train-borne ATC equipment .ATC has three functionality which includes ATO ,ATP and TDM .Refer section 1 for details of individual system within Train borne  ,Trackside and  Wayside (ATO, ATP ,TDM ,Antenna ,DCS ,Balise )  2.3.     Role of Interlocking Interlocking is an arrangement of signalling appliances in which operation of one appliance will depend on the status of other in a proper sequence to ensure safe conditions . In other words  Interlocking is a failsafe system  responsible for  controlling ,gathering vital equipment  status , locking and releasing  trackside equipments such as Signals ,Points and other equipment .There could be various other trackside equipment   such as stop Plungers , track circuits ,and wayside equipments such as  control panel for degraded operation .These are part of the non-core functionality of the CBTC  which varies from operator to operator for train recovery ,maintainers protection, diagnostics ,fall back mode etc   .There will be a dedicated interlocking chapter published in RailFactor  in future. 2.1.1     Launching of Train from Depot to Mainline  Based on time table , ATS automatically set a route for the train consists 1   assigned with a head code ,entered by the operator so as to allow the trains to reach its destination  without having the operator to set route manually.ATS will send the route request in advance to the interlocking to set the route before the departure time .Once the route is set ATS will remotely send the wake up command to switch Train 1 On .Upon receipt of this command on ATC computer (ATP/ATO) of Train 1  perform a wake -up test automatically. This wake-up test will test the operational and safety capabilities of the train-borne ATC(ATO /ATP/TDM)  system and its interfaces with the train and other subsystems .TDM will provide the front end processing for interface between ATC and Train Integrated Management system of the train. This is to allow data transmission between TIM of Train and ATC. As part of the wake-up test ,ATP system confirm that the train 1 has not moved during sleep and train position is known. Wake up sequence commence with door closed. In case door is open, then TDM (Train Data Management) will request door closed and check doors are closed prior to commencing the wake up sequence .In case door failed to close  an Alarm will be send to the ATS .Train will verify its geographical position through the balises  and its transferred to the  Train Borne equipment. When train is ready to start his ride ,ATP will send a signal to the relay /brake encoder panel of the train to release brake and train  1  takes the  route assigned to it and commences the journey  from depot to the mainline reception track  .Train 2 follow the same process following the initiation from ATS based on  Time table and enters into the main line reception track from depot following Train 1  (maintaining a headway of 3 min) . Train 3 will follow Train 2 maintaining headway of 3 min with Train 2. As shown in Fig 4, Train 2 will maintain a safety margin with train 1. This safety margin is based on various parameters such as Train 2’s  braking characteristics ,gradient of the track etc. In nutshell when Train 1 stops on platform 1, Train 2 will apply service brake to maintain safety margin by either reducing speed or a complete halt, until he can maintain safety margin with Train 1. All the trains are updating the geographical position and speed to the wayside  ATC system and receives a movement Authority continuously .Thanks to  the bi-directional ,radio system making continuous communication  between wayside to trackside(wired)  and trackside to the train (wireless).When Train passes  over the balises ,it update the position and send to the wayside ATC    Fig 4 ATC Train Operation   3. Summary     This article  covers the general operation using the core functionality of a CBTC system ,non core functionality  such as monitoring ,maintenance ,train recovery ,cut over etc are subject to operators requirement and are out of scope for this article.This will be covered in another article

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Jyoti TV -
Posted 37 days Ago

Have a job interview coming up? Pre-interview preparation Step

General

  Are you getting ready for a job interview?  A practice run can provide you with the necessary preparation to ace the real thing. A quick read-through of the Article published in RailFactor may also help you. Your success in a job interview is heavily reliant on how well you prepare for it. Interview preparation primarily entails researching the job and the company, as well as carefully considering your responses to interview questions. Listed 5 Pre-interview preparation Steps which may help to grab your dream job. PRE-INTERVIEW PREPARATION - STEPS TO GET YOUR DREAM JOB Review the job description Review the keywords and key phrases in job description Refresh your skills and add certification Are you eligibile Ask the questions. Am I right fit. Why the employer should hire you.  Know the company Find out vision, mission, management, work culture and types of products/service.  Prepare a list of expected interview questions Tell me about yourself. Why are looking for a job change? What are your strengths and weaknesses? Update your social media profile Employers may look at your social media presence to get a sense of your personality and history.

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Deepu Dharmarajan -
Posted 40 days Ago

Automatic Train Supervision (ATS) System

Automatic Train Supervision

The system that monitors and provide necessary commands to direct the operation of Trains in order to maintain the schedule in the required traffic patterns to minimise the effect of Train delays. Automatic Train Supervision System (ATS) is part of the Automatic Train Control (ATC) along with Automatic Train Protection System(ATP) .Refer Figure 1 for  the relation .Primary Function of an Automatic Train Supervision(ATS)  is to control and monitor the train operation .ATS is managing the train operation according to a time table or a specific headway or based on human (operator ) interaction on degraded mode of operation. A modern day ATS includes Automatic Train Regulation (ATR) and a Schedule Compiler. Figure :1 Block Diagram of Automatic Train Control ATS provide interface for the operator to supervise and manage trains. It provide real time status of the operating positions of the trains. ATS control launching of trains from storage facility to the commercially operating line and return the trains from operating lines to storage facility. It can also send manual and automatic commands to initiate and terminate train operations with override automatic command functionality. Modern day ATS system has some of the following functionality. Operator can create and modify timetables. Operator can monitor and control real time trains Automatically send route call requests according to train operation requirements Automatically send traffic locking calls based on train operation requirements Automatically regulate train movements based on regulation needs. Allow restore services and re-establish train operating patterns due to service delays and breakdowns Tracking Train Positions in all signalled area. Manage events and alarms from signalling system, trains and other signalling subsystems. Supply real time train information to Public addressing system. Generate performance reports for train service availability and train service quality factor. Allow automatic and manual taking over of control centres, if have multiple control centres for redundancy purpose. Capable of remotely control to open and close train doors and Platform Screen Door, if present Can build centralized functionality and localized functionality. Can build Train Description Facility for tracking and maintain a record of each train. Functionality of a Modern Automatic Train Supervision System Automatic Train Regulation (ATR)   Modern Day Train Automatic Train Supervision can regulate the train based on various train regulation strategies under automatic mode .It can dynamically regulate trains to maintain headway and time table .Automatic Train regulation allow operator to configure the level of service deviation and raise an alarm to the operator if the service deviation exceeds the set level.ATR functionality within ATS  can incorporate some of basic train regulation strategies. 1.1 Timetable Adherence ATR feature of the ATS monitor real time train services to ensure they are on schedule. It recover services making use of corrective actions to maintain time table .Corrective actions can be  taken by adjusting station dwell times ,run times ( within the maximum speed of the track ) , coasting and adjustment of headway 1.2 Headway ATR monitor the train services to ensure constant headway is maintained. Best suitable headway is selected based on number of trains allocated by operator (without exceeding the maximum number of trains possible within designed headway, usually 88 seconds or more ) .ATR can even alert the operator if he /she allocate more trains or headway if he/she exceed the limit . Automatic Route Setting (ARS) facility ATS  is capable of automatically make route calls based on train location ,time table and route strategies .ATS will not send a route call repeatedly to the interlocking if the route is not available .Rather it check route is already set by other request ,route is blocked or the requested route can cause a dead lock around terminal or turn around areas .Unlike  any other Entry-Exit ,or one control switch control system ATS can  store any route request and retry only when the route become available. In case the controller block a route and next controller try to set the route, ATS can alert the operator with the reason. ATS can automatically identify conflicting routes and when two trains approach a station can give priority to the train set which is scheduled to use the station first. ATS can allow override of automatic route setting for a manual route setting when needed. ATS ensures it will not set a route for an arriving train at a junction or a station platform which restrict a departing train to leave the platform Manual Route Control facility ATS can allow to perform manual route setting which can override the auto route setting. On modern day ATS you can find blocking and unblocking of signals and points for easy maintenance purpose with controlled reversal to avoid human error. Station Dwell Time adjustments As required operator can adjust station dwell time which can override the dwell time proposed by the timetable or ATR without affecting the T minimum Dwell time. Platform Hold ATS can allow the operator to prevent trains from station and hold. ATS can allow auto hold as well based on known scenarios. As an example, if at a time two trains cannot be at same place in one tunnel ventilation system, ATS apply hold functionality to halt one train at a station ,not allowing two trains comes to same section at same time. Similarly, when there is a fire in some tunnel section ATS can apply hold for trains in adjacent station. Train Hold ATS can allow the  operator to hold  and release a Train  at a station with status display on the workstation Skip Stop ATS can allow operator at an operating terminal to make a train skip a station or more as desired. When a hold command is applied before skip command, hold command take precedence over skip command as hold command could be  more related to fire and other safety related issues . Train Control ATS allow Train controller to manually control the train by sending remote wake up and sleep command. Command are normally issued automatic based on schedule or manually by an operator from a control terminal. ATS can also send command to  reset train borne ATC equipment. Operator can also send emergency brake release command. This will be ensured when ATC confirm its safe to release. Operator can have a remote command to open and close a train door when the track side equipment confirm its safe. In case there is a Platform Screen Door present in the system , command is   simultaneously issued to Platform Screen Door controller to open /close concurrently with the train door.ATS can also send a creep mode command to a train in automatic mode but suffers a ATO failure. Temporary Speed Restriction (TSR) An operator from his control terminal can apply and remove temporary speed restriction with immediate effect for any direction of travel in entire signalled area .It can also apply for a  track circuit section .TSR can vary from 0Km/Hr to the maximum design speed of the system. Mode Inhibition ATS can allow the operator to inhibit the mode of operation such as Automatic Mode(Grade of Automation 3/4)  ,Manual Mode(Grade of Automation 0 or 1)  ,Semi Auto Mode(Grade of Automation3)   for a train or entire fleet along the signalled area . Time Table ATS allow the operator to modify the running time table as per demand with in allowed headway and maximum trains possible in the line for that headway .Operator can create ,modify or delete a time table ,service ,trip or suspend a time table .In case by mistake operator suspend a time table ,ATS can allow through a command to resume from the current time. Controller workstation allow to load new time table ,modify origin ,destination ,dwell time ,arrival /departure time ,inter station run time ,coast level with recording of the controllers action on parameter change with time stamp. Operator can download the time table and send for printing. Energy Optimisation Based on traction power supply limitation ATS can optimise energy consumption by avoiding waking up trains at same time from same power zone to minimise rise in current. Alarm and Events ATS can alert the operator on any faults as needed by the operator through alarm ,warning based on the severeness  of criticality .Pre-emptive warning of any subsystem can also be alerted .Various railways use different background /text colour code for severity level .Severity level are configurable based on needs .ATS can also log and record events with time stamp and link with maintenance facility Automatic /Manual Take Over Depends on railway requirement there could be Main Control Centre ,Back up Control Centre ,Station Control Centre ,Depot Control Centre etc .In case of failure of Main Control Centre ATS server or Loss of communication between Station and Main Control Centre ,Station ATS can take over control to avoid traffic disruption .An operator at Main Control Centre  can manually  request take over control from another operator  at Station Control Centre Automatic /Manual Hand Over Over Similarly Handover can be done between control centre and Operator. Modern Day Automatic Train Supervision Refer Figure 2 for Modern Automatic Train Supervision System block diagram .Interconnection to other subsystem is out of scope for this article which will be covered in Architecture of a CBTC   Figure 2 Typical Automatic Train Supervision Interface 17. Summary Automatic Train Supervision System paved way for a highly capable automatic  “vital “ control centre from conventional “Non Vital “Entry-Exit Control Panel or a One Control Switch Graphical User Interface Control Terminal .In a modern train control system ,especially Automatic Train Control system used in Communication Based Train Control System ,ATS has a significant role .

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Pravin_pasare -
Posted 40 days Ago

Slab track VS Ballasted Track

Rail Tracks

No. DESCRIPTION BALLASTED TRACK BALLASTLESS TRACK 1.       Maintenance Input. Frequent maintenance & non-uniform degradation Less maintenance for geometry. 2.       Cost comparison Relatively low construction costs but higher life cycle cost. Relatively high construction cost but lower life cycle cost. 3.       Elasticity. High elasticity due to ballast. Elasticity is achieved through use of rubber pads and other artificial materials. 4.       Riding Comfort. Good riding comfort at speeds up to 250 – 280 kmph. Excellent riding comfort even at speeds greater than 250 kmph.   5.       Life expectation (20 yrs) (50-yrs) 6.       Stability. Over time, the track tends to “float”, in both longitudinal and lateral directions, as a result of Non-linear, irreversible behaviour of the materials. No such problem. 7.       Lateral resistance Limited  compensated Lateral acceleration in curves, due to the limited lateral resistance offered by the ballast. High lateral resistance to the track which allows future increase in speeds in combination with tilting coach technology. 8.       Noise. Relatively High noise Relatively low noise and vibration nuisance. 9.       Churning up of Ballast. Ballast can be churned up at high speeds, causing serious damage to rails and wheels. No such damage to rails and wheels. 10.  Construction cost of Bridges/Tunnels/ etc. Ballast is relatively heavy, leading to an increase in the costs of building bridges and viaducts if they are to carry a continuous ballasted track. Less cost of construction of bridges and viaducts due to lower dead weight of the ballast-less track. 11.   Construction Depth. Depth of Ballasted track is relatively high, and this has direct consequences for tunnel diameters and for access points. Reduced height.

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Deepu Dharmarajan -
Posted 44 days Ago

 Modern Train Control Systems

CBTC

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

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Deepu Dharmarajan -
Posted 69 days Ago

SIGNALLING A LAYOUT | PART 3

Signalling

CONTINUED FROM - SIGNALLING BOOK | CHAPTER 3 | PART 2 SIGNALLING BOOK | CHAPTER 3 | PART 3 CONTENTS 1. Introduction - In Part 1 2. Headway - In Part 1 3. Positioning of Running Signals - In Part 2 4. Types of Signal - In Part 2 5. Points and Crossings - In Part 3 6. Track Circuits - In Part 3 7. Identification of Signals, Points & Track Circuits - In Part 3 8. Examples - In Part 3   5. POINTS AND CROSSINGS Although, in general, the siting of points and crossings on an existing railway will be dictated by permanent way design considerations, it is left to the Signal Engineer to determine the operation of the points. Furthermore, the Signal Engineer may require additional trapping protection to be provided on occasions and such cases must be referred back to the Permanent Way Engineer or other responsible engineer. In the case of combined track remodelling and resignalling projects, it is sometimes possible to provide simpler or improved signalling controls by minor alterations to the track layout. Close co-operation between the Signal Engineer and the Permanent Way Engineer is essential if the optimum results are to be achieved. 5.1. Position and Numbering of Points Any set of points will be defined as lying in its Normal position for one route and its Reverse position for the other route. The Normal position of the points will be shown on the signalling plan as follows:- A similar convention applies to switched diamond crossings, if used. Points should be numbered in such a way that any point ends required to work simultaneously carry the same number. To localise failures, it is not advisable to number more than two ends to work together. In addition, Solid State Interlocking (SSI) equipment is normally only configured to operate single and double ended points, although in certain circumstances three ends can be accommodated. For control purposes, each end has to be identified separately (A or B) but this may not need to be shown on the signalling plan. A convention must be determined for identifying A and B ends (e.g. A end nearest control centre or A end at lowest reference distance etc.) and strictly observed. On TfNSW network  a down train will meet the A end first. 5.2 Ground Frames Ground frames control infrequently used points, usually outside interlocking areas. Although referred to as ground frames, they may equally well be locally operated control panels. In its most common form the ground frame consists of just 2 levers, the point lever and a release lever (which will also work the F.P.L. if the points are normally facing). Movements over the points during shunting are usually controlled by handsignal, although extra levers may be provided to control or slot signals which the train must pass during shunting. Note the use of separate releases where the ground frame controls more than one function. Instead of providing an electric lock on the release lever, a separate key is electrically released when the signalman operates the release button. This key is then used to release the ground frame release lever. It remains captive until the ground frame is normalised and can then be returned to the instrument to give back the release. 5.3 Trapping Protection It may be necessary to request trap points (normally known as catch points on TfNSW) to be provided at certain locations: At the exit from sidings, where they lead on to running lines, catch or trap points must be provided to prevent an unattended vehicle running away or a shunting movement overrunning and fouling the running line. Where a full overlap cannot be obtained and movements are required to closely approach a converging junction, catch or trap points leading away from the running line can be used as an overrun in place of the normal overlap. On railways where a distinction is made between passenger and non-passenger lines, trap points may be used where the non-passenger line joins the passenger line. Where trap/catch points occur in track circuited lines many railways employ a track circuit interrupter to ensure a derailed vehicle which is still fouling the track, although not standing on the rails, remains detected. The track circuit interrupter is normally insulated from the rail on which it is mounted and bonded in series with the opposite rail. 6. TRACK CIRCUITS Track circuits shall be provided in a manner which permits maximum flexibility with minimum expense and complexity. 6.1 Overlaps Running signals should, in general, be provided with separate berth and overlap track circuits, the berth track circuit terminating immediately beyond each signal. This will ensure the signal is replaced to danger at the earliest opportunity after the train passes. Where more than one overlap is required, a joint must be provided at the end of each overlap. Calculation of overlaps has already been covered in the earlier sections dealing with the positioning of signals and trainstops. However, old TfNSW  practice on overlaps is summarised below. 6.1.1. Where Trainstops Are Not Fitted The overlap is a margin to allow for braking errors. There is no positive means of stopping the train if a driver completely misses or misreads a signal. As such it is an approximate distance based on experience, rather than one which has been calculated on any scientific principle. The standard SRA overlap is 500 metres. This may be smaller or greater than the actual braking distance. Where speeds are low, this is sometimes reduced. Recommended overlap lengths are:- 6.1.2 Sydney Metropolitan Area (Open Sections) If  trainstops are fitted,(recently ATP rollout has taken place which will remove the significance of  mechanical trainstop) the overlap must be based on emergency braking distance for the prevailing speeds and gradients. The following example shows how this may be calculated. To simplify the calculation when dealing with gradients it is often easier to express the braking rate as a percentage of the acceleration due to gravity (g = 9.8m/s 2 ). Braking distance = v 2 /2a (where a = braking rate, v = train speed) = 100v 2 /2g(%B + %G) %B = Braking rate as a percentage of g %G = Gradient as a percentage (down gradients negative) If the line speed is 25 m/s, the braking rate is 10% and the gradient is 1% down, the emergency braking distance and hence the overlap will be:- 100 x 25 2 / 2 x 9.8 x (10 - 1) = 62500 / 176.4 This would give a minimum overlap of 354 metres. This would probably have to be increased by a suitable margin to allow for less than 100% braking performance (e.g. some brakes isolated, wet or greasy rails, delay time for brake application). Where available, braking tables or curves should be used. If the full overlap is foul of junctions or station platforms, a reduced overlap should be considered. The train speed would have to be suitably reduced by a low speed or conditional caution aspect at the previous signal. 6.2 For Points and Crossings The positioning of track circuit joints to prove clearance will depend on the dimensions of the rolling stock in use. One must first determine the difference between the maximum vehicle width and the width of the widest vehicle in service. The position must then be found where the rails leading away from the crossing are at least this distance apart (normally adding a small safety margin). At this point, the extreme ends of vehicles on the adjacent tracks will not be foul of each other. Measuring away from this position, the joint must be located at a distance greater than the maximum end overhang of any vehicle. This is obtained by measuring from the centre of the outer axle to the extreme end of the vehicle. Track circuits should allow maximum flexibility of use of the layout. In particular, where the track layout permits parallel moves, the signalling must not prevent them. Joints should be positioned to achieve the earliest release of points after the passage of a train consistent with safety, economy and practicality of installation. Example 1 Joint A allows simultaneous moves over both ends of crossover normal. Joint B allows points to be moved as soon as train leaves points. Joints C, at clearance point, allow movements across crossover with Tracks X and Y occupied. It is common on plans to place joints C opposite the tips of the points. Example 2 Joints A allows parallel moves. Joints B allow points to be freed as soon as junction cleared. Joints C are set back at clearance point. These may also be the overlap joints for signals approaching the junction. Joint D will be dependent on factors other than the requirements for operation of the junction, eg. the position of the protecting signal. 7. NUMBERING OF SIGNALS, POINTS AND TRACK CIRCUITS To enable all signalling controls to be specified, each signalling function must be uniquely identified. It aids design, testing and fault location if this is done in a logical and orderly manner. In particular, confusion is avoided if different types of functions are numbered in different number or letter series. The main functions which need to be numbered are:- Main Signals Shunt Signals Points Track Circuits Ground Frame & other releases Separate number series should be provided for each type of function (points, signals etc.). Main and shunt signals may be numbered in the same or separate series. Lines for each direction of traffic are normally designated UP and DOWN. Signals reading in the Down direction normally carry odd numbers with the lowest number at the Up end of the control area. Signals reading in the Up direction normally carry even numbers, again with the lowest number at the Up end. Points will be numbered with the lowest number at the Up end of the control area. Where possible suitable gaps should be left in the numbering sequences in anticipation of future alteration. Distinct branches should be numbered in separate series. Historically, several different conventions have been used for identification of track circuits. Each has advantages and disadvantages. One common method is to use a simple numbering sequence. The disadvantage of numbers is that, on a large installation, very large numbers or duplicate number sequences need to be used (with greater risk of errors in design and testing). Another alternative which has been used is to number track circuits based on the distance along the line. This results in track circuits in one locality having long and very similar numbers. Again confusion and errors may result. TfNSW  uses a system based on the signal numbers. The first track past signal 5 would be 5A, the next 5B and so on. The suffix E is not normally used. The BR standard is now to use letters. Each track circuit indicated to the signalman should be identified using two capital letters, arranged alphabetically in a logical sequence. Letters I and O are not used. Where a number of track circuit sections have a common indication they should have the same identity plus an individual suffix number, eg. AA1, AA2 etc. This arrangement is simple but does not give any indication of the relative locations of tracks and signals. 8. EXAMPLES A few examples are now given of some of the more commonly found track layouts and suggested arrangement of signals. They do not cover all situations. In practice, different requirements will conflict. The signal engineer must resolve these conflicts in the most effective and economic manner 8.1 Junctions The logical arrangement at a junction is for the protecting signal to be as close to the junction as possible. For diverging movements this ensures that trains are not checked too far from the junction, while for converging movements it reduces the chances of trains being checked due to conflicting moves on the junction. The signal next in rear of the junction cannot be cleared unless the section is clear up to the junction signal, and the overlap beyond. It is preferable that the overlap is not fouled by conflicting moves, so ideally the signals protecting the junction should be placed overlap distance in rear of the junction. If large overlap distances make this impractical, a reduced overlap clear of the junction should be considered. In this case the signal in rear should have its full overlap clear of the junction. 8.2 Station Platform with Loop It is usually desirable for headway reasons to site a signal at the end of the platform. This provides a platform starting signal and also protection for any level crossing at this point. In situations where there is no platform starting signal, there is a risk that a station stop will divert the driver's attention sufficiently for him to forget the aspect displayed by the previous signal. After restarting his train, he could approach the next signal at an unsafe speed. In the above example, signal A is located at full S.B.D. from signals B & C. For main line running this is satisfactory, but for a move into the loop the time taken for the train to slow to 25 km/h over the crossover may adversely affect the headways. A better arrangement is shown below : Signal A is moved closer to the turnout. If this results in inadequate braking distance from signal A to signals B & C, signal D must be a 4 Aspect signal. Signal A would only need to be 4 aspect if the signal ahead of C was less than braking distance. 8.3 Terminal Stations The station throat track capacity must be at least double that of the approaching line. This is because some arriving and departing movements will completely block all other routes. The signal reading into the platforms should be as close as possible to the plaforms. If this signal does not have an overlap clear of points, the signal in rear should do so to allow trains to approach unrestricted. Signal spacing on the approach to the station should be as close as possible consistent with standing room and headway requirements. The first signal leaving the station should be as close as possible (whilst retaining necessary train standage clear of the pointwork), to allow the best possible aspect on the platform starting signals. The standage requirement may have to be reduced to maintain adequate line capacity on the departing line. The platform entry signal 3 exhibits stop and caution aspects only for running moves. Buffer stops are equivalent to a signal permanently at stop. Subsidiary shunt signals are provided to enable trains or locomotives to enter occupied platforms. If wrong line shunting is required, a shunt limit board must be provided at a position which permits adequate standing.  

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Jyoti TV -
Posted 72 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 105 days Ago

SIGNALLING A LAYOUT | PART 2

Signalling

CONTINUED FROM - SIGNALLING BOOK | CHAPTER 3 | PART 1 SIGNALLING BOOK | CHAPTER 3 | PART 2 CONTENTS 1. Introduction - In Part 1 2. Headway - In Part 1 3. Positioning of Running Signals - In Part 2 4. Types of Signal - In Part 2 5. Points and Crossings - In Part 3 6. Track Circuits - In Part 3 7. Identification of Signals, Points & Track Circuits - In Part 3 8. Examples - In Part 3 3. POSITIONING OF RUNNING SIGNALS If we are starting with a blank track layout, we need a logical method of setting out the signals in order to produce a signalling plan. As running signals must fulfil the needs of both headway and braking distance, it is usual to position running signals first. Shunting and subsidiary signals are dealt with after the running signals have been placed. 3.1. Headway Constraints First plot the positions of the running signals on the principal running lines. Then proceed to lower priority lines in order of importance. It is often difficult to decide where to start. If a station exists on the layout it is usual to start by plotting platform starting signals, and then continue by plotting the signals in rear and in advance to be within the tolerance of minimum separation (for braking distance) and maximum separation (for headway) for the type of signalling to be employed. It is also desirable to position signals close to facing points at junctions so that the driver does not have a long distance to travel to the turnout. This will minimise delay to traffic and reduce the possibility of signals being misread. Service braking distance must be provided from the first cautionary aspect to the signal at danger in every case. The maximum distance from the first caution to the red is set by the headway requirement. Ensure that any large excess over service braking distance is within acceptable limits. 3.2. Other Constraints In addition to headways, other constraints must be borne in mind. These include junctions, further stations, tunnels, viaducts and level crossings. There may be many places where it is required to stop a train for operating reasons. The engineer will have very little choice in the position of these signals. Conversely there are also many places where it is highly undesirable to stop a train and signals must be positioned to avoid these. Other factors to consider are the visibility of the signal to the driver, the practicality of installing a signal at a particular site and ease of access for maintenance. Signal A has been placed at a distance greater than service braking distance from B because it would have otherwise stood on the points 201. If a line is generally signalled with 2 or 3 aspect signals and it seems necessary to have two signals spaced closer together than service braking distance, remember that the next signal in rear must be capable of displaying a medium aspect to give an earlier warning of the need to stop. If a suitable signal does not already exist, an additional signal will have to be introduced. A signal should be positioned so that a train stopped at that signal does not: Stand in a tunnel (wholly or partially). This would not apply to underground passenger railways where special provision has been made in the design of the trains and/or tunnels to ensure the safe evacuation of passengers in an emergency. Stand on a viaduct, unless special provision has been made for safe evacuation of passengers and/or access by emergency services. Foul a junction. Stand partially at a platform (unless the passenger doors can be kept closed by the train crew). There are occasions when, due to local circumstances, these requirements cannot be wholly met but every effort should be made to comply. Additional considerations will apply on electrified lines to ensure that trains are not brought to a stand in neutral sections or gaps in the conductor rail. If possible, heavy freight trains should not be stopped on steep falling or rising gradients, especially in combination with sharp curves. 3.3. Examples of Standage Constraints Ensure maximum length train can stand in platform. Ensure that maximum length train can stand clear of junction fouling point to allow other movements to pass behind it. Signals on adjacent running lines should as far as possible be placed opposite each other. This minimises the chance of drivers reading the wrong signal. It also simplifies the design and installation of power supply and location equipment. 4. TYPES OF SIGNAL Running signals may be divided into three general groups according to the form of control exercised by the signalman. 4.1. Automatic Signals Automatic signals are designed to operate only according to the presence of trains on the track circuits ahead. The signalman does not have to set the route for each train. Usually he will not have any facility to set routes but may in certain circumstances be provided with a switch or button to replace the signal to danger in emergency. A signal may be shown as automatic if all the following conditions can be met:- No points in the route to the next signal. No points in the overlap beyond the next signal (Exceptionally, simple facing points may be allowed). No directly opposing routes within the route or the overlap. No ground frames, controlled level crossings or other equipment with which the signal must be interlocked. The normal aspect of an automatic signal (i.e. the aspect shown when there are no trains present) will generally be a proceed aspect. As the signalman is not directly concerned with the operation of automatic signals, some other facility may be required to stop trains in an emergency. If it is decided that this facility is required, options available are:- Individual replacement switches or buttons on the signalman's panel (for all automatic signals or selected signals only) Grouped replacement switches or buttons. Each one can replace a group of consecutive signals on the same line to danger) A replacement switch mounted on or near the signal, usually requiring a special key to operate. Earlier British practice was to provide replacement facilities on automatic signals in any of the following circumstances:- Controlling the entrance to a section in which a level crossing equipped for automatic operation is situated. Controlling the entrance to a section in which a tunnel or viaduct is situated. Controlling the entrance to a section in which an electrical traction break is situated. If not otherwise required, on at least every fifth signal in any section of automatic signals and at any other signal where required for operating purposes. Since the accident at Clapham Junction in 1988, this policy has now changed to one of providing some form of emergency replacement for all automatic signals. On all new installations, this is by means of an individual button on the panel. Automatic signals must be recognisable as such to the driver. In the event of a signal failure and loss of communication with the signal box at the same time, the driver can then pass the signal at danger and proceed at extreme caution to the next signal (prepared to stop short of any obstruction). Some railways identify their automatic signals by a different style or colour of identification plate. SRA (TfNSW) practice is to offset the lower signal lights (or marker light) 204mm to the right of the upper signal lights. If clearance constraints make this impossible, and the lights must be in line, a separate plate with a white letter A on a black background is provided. 4.2. Semi-Automatic Signals In many areas signal boxes or local ground frames are provided which provide access to sidings or are not continuously manned. Signals must be provided which permit through traffic to operate when the frame or signal box is unmanned. These signals have to operate automatically for much of the time but must also be capable of control by the local operator. Semi-automatic signals are provided in this case. When the signal box is switched out or the local frame is locked normal, the signal functions as an automatic signal. Once again, the driver must be aware of the correct action to take in the event of failure. A distinct identification plate is used on some railways. The driver must then confirm that the ground frame or local signal box is not in use before treating it as an automatic signal. SRA (TfNSW) practice is to provide an internally illuminated "A" indication below the semi-automatic signal (which otherwise has the same appearance as a controlled signal). The "A" is illuminated only when the signal is working automatically. It may also be necessary to divert any signal post telephone circuit to another supervising signal box when the local control is not in use. 4.3. Controlled Signals Any signal other than those described above will be a controlled signal. It must be controlled from a signal-box (other than by Emergency Replacement). It will usually require a lever, switch, button, key or plunger to be operated for each movement. Controls may be provided to allow a controlled signal to operate automatically (i.e. without re-setting the route for each movement). It must be decided whether this should be apparent to the driver. BR practice is not to provide any distinct identification on the signal. The driver will always treat it as a controlled signal, even when working automatically. This is because it is unsafe to adopt any form of "stop and proceed" working where there are points ahead of the signal which may be moved. A signal will normally be "Controlled" if there are points and/or conflicting routes in the route or overlap. 4.4. Signal Identification Plates All stop signals and/or all signals provided with a signal post telephone should be provided with an identification plate. As stated earlier this may be of a different style according to the type of signal (controlled, automatic or semi-automatic). When talking to the signalman, the driver should be able to identify where he is, even if this information is also shown on the signalman's telephone equipment. Other signals (e.g. distants and repeaters) may also be identified for maintenance requirements. Some controlled signals in particular positions may need to be specially identified. For example, the "accepting" signal on approaching an interlocking from a section of automatic signalling is specially plated to remind the driver that he is no longer under the control of automatic signals. 4.5. Signal Aspects Having decided on the necessary position of each running signal on our plan, we must now ensure that we depict each signal to show the correct combination of signal aspects. This will be governed by two main factors:- the type and distance of the next signals ahead; whether it is necessary to give warning to the driver to stop. whether the signal or the next signal ahead is a junction signal. Any signal that has more than one running route is a junction signal and, as such, must provide the driver with the appropriate turnout aspect and/or route indication when required. For all junction signals on the signalling plan, an adjacent box should be included showing the signal number, description of each route, its exit signal, and the route indication (if any) displayed. 4.5.1. Aspects for Through Running (Single light) In single light signalling areas a stop signal must at minimum have a head with a red and a green light, with a marker light below. If the next signal ahead is a stop signal at greater than braking distance, a caution aspect must be provided. If the signal ahead is at less than braking distance and the following signal section is also shorter than braking distance, the signal must display also a medium (pulsating yellow) aspect. The signalling plan will show a letter "P" against the signal to indicate that it displays a pulsating yellow aspect. If there is braking distance between the next two signals, the medium aspect is not required. Single light signal heads capable of showing only two lights should be shown on the signalling plan with the actual colours required (R for red, Y for yellow and G for green). Distant signals will usually display caution and clear only. If there is inadequate braking between the next two adjacent stop signals ahead, a medium aspect (pulsating yellow) will also be required. 4.5.2. Aspects for Through Running (Double light) All double light signals have two signal heads, one below the other. The top head is the stop signal and the lower head is the distant for the signal(s) ahead. If the signal is not a junction signal, the upper head will be red & green only. The form of the lower head will depend on whether three or four aspects are required. The, rules are exactly the same as for double light but the aspects are different. The lower (distant) signal head will display red and green only for 3 aspect signalling, red,yellow and green for 4 aspect. The provision of low speed aspects is dealt with elsewhere in these notes. 4.5.3. Junction Signalling (Single Light) The indication of a route diverging from the main line will be by either a turnout signal (maximum of one route to left and/or right) or a multi—lamp route indicator in conjunction with the main aspect (more than one route to left or right). When the turnout signal is used, the main signal remains at red. All turnout signals must be capable of displaying a caution (three steady yellow lights) and may display a medium turnout aspect (three pulsating yellow lights) when the signal ahead is showing a proceed aspect. When a route indicator is used, the main signal will display a steady or pulsating yellow (according to the next aspect ahead) and the appropriate route indication will be displayed. Clear signals are not given through turnouts. 4.5.4. Junction Signalling (Double Light) The indication of a turnout on a double light signal is by a yellow in the upper signal head. All junction signals therefore require an upper signal head with red, yellow and green lights. The lower signal will still indicate the state of the signal ahead, red if the first signal ahead past the junction is at stop, yellow if the next signal displays a proceed aspect. If a junction signal is set for the turnout (either caution or medium) the previous signal will display a medium aspect, never a clear. Route indicators may be used where two or more turnout routes exist. 4.5.5 Low Speed Signals Section 2.5 has dealt with the main situations in which low-speed signals are used. Firstly, check whether a conditionally cleared caution could adequately fulfil the operating requirements (the overlap should be at least 100m for a conditional caution). Low speed signals are not necessary for normal through running. They should, however be considered in cases where reduced overlaps can aid the regulation of traffic and/or headway for stopping trains and a conditional caution is not appropriate. It is also recommended to provide low speed signals through any area where a track circuit would otherwise control three or more running signals. This is to localise the effect of failures by restricting the number of handsignalmen required in the event of track circuit failures. 4.6 Shunting and Subsidiary Signals Having catered for all running moves, we must now provide for shunting and other non-running movements. Before starting to place signals on the plan, make sure you know exactly what movements are required. Any movements which are not signalled will have to be authorised by handsignals. Handsignalled movements on lines where the majority of trains are properly signalled are disruptive to normal traffic and allow the possibility of human error. Conversely, signals provided for movements which are never used are an additional and unnecessary initial cost to the project. They also represent a continuing maintenance cost and a potential source of additional failures. Although the terms are often used interchangeably, there is a distinction between shunting and subsidiary signals. Subsidiary signals are part of a main running signal. Shunting signals are independent. Subsidiary signals therefore only need a proceed aspect - the main signal provides the stop aspect. Shunting signals must display both stop and proceed aspects. Subsidiary signals can broadly be divided into the following functions:- To shunt from a running line (in the normal direction of traffic) into a siding. To move forward from a running signal into an occupied section. A main route to the same destination may already exist. The provision of both main and shunt routes could assist operations in critical areas during track circuit failures. On a multiple track line, to shunt on to another line in the opposite direction to normal traffic. To move forward to a shunt signal facing the normal direction of traffic. On absolute block lines, to permit a train to pass the starting signal at danger for shunting purposes only. The shunting movement must return behind the starting signal Unless the movement is on to a section of line which is not fully signalled there will need to be an exit signal to limit the extent of the movement. Independent shunting signals can broadly be divided into the following functions:- To shunt between running lines from a position where no main signal is provided. To enter, leave or shunt between sidings. To shunt in the opposite direction to normal traffic. To limit the extent of any shunting movement (including "shunting limit" boards). The diagram below shows examples of some common applications of shunting and subsidiary signals. 4.6.1. Calling-on and Subsidiary Shunting Signals This will be provided where a movement must be authorised to pass a main signal at danger to enter a section which is or may be occupied. An example would be the coupling of two portions of a train in a station platform. Signal 4 on the diagram has a subsidiary provided for this purpose. The usual aspect displayed is a miniature yellow. Some older double light signals display an internally illuminated "CO". 4.6.2. Dead End Signal This will be provided where a movement must be authorised to pass a main signal at danger to enter a dead end siding via a facing turnout from the main line. It displays a miniature yellow light and is offset to one side of the signal post (according to the direction of the movement). Signal 5 is an example of this. 4.6.3. Shunt Ahead Signal Used to shunt ahead of the starting signal and mounted below the main signal. Used on single light signalling only and displays a pulsating miniature yellow light. Signal 7 is provided with a shunt ahead signal to enable long trains to draw forward past the signal before shunting back over the crossover. This type of signal will normally be found in single light signalling areas only. 4.6.4. Dwarf and Position Light Shunt Signals Shunting signals normally have two aspects - stop and proceed. The stop aspect is two red lights and the proceed aspect is a single yellow light. This instructs the driver to proceed at caution. It does not guarantee that the line ahead is clear. SRA (TfNSW) uses both dwarf and position light shunting signals. The difference between the two types of signal is the orientation of the lights. The choice of signal type will depend mainly on lineside clearances. On a position light signal, the two red lights are side by side, the yellow light is above. A dwarf signal has the three lights vertically arranged; the red lights are at the top and bottom with the yellow light between. Route indications are provided where required, particularly where wrong line movements are signalled. 4.6.5. Shunting Limit Boards Effectively a shunting signal fixed at danger, a shunting limit signal faces in the opposite direction to normal traffic and is used to limit the extent of a wrong line shunting movement. An example is shown on the down line. This would enable trains to shunt out of No. 1 siding on to the down line before proceeding forward. Without the board there would be no signal to prevent the wrong line movement continuing indefinitely on the down line. 4.6.6. Facing (or Preset) Shunt Signals Occasionally, shunting movements in the normal direction may be required to start from a position where a running signal is not provided. Such a shunt signal must therefore be passed by normal running movements. To avoid the driver seeing a yellow light after he has just passed a main signal showing clear (and possibly braking unnecessarily) "facing" shunt signals are provided with an additional green light to show clear when the previous main route is set past the shunt signal and the signal is showing clear. Signal 55 is a facing shunt signal. 4.6.7 Point Indicators Point indicators should be provided on any points (whether facing, trailing or catch points) where the driver is responsible for observing the position of the points before proceeding over them. The points will usually be hand worked, as shown in siding 1 on the example. Where regular shunting takes place without the need for the signalman to set the route for every move, point indicators will be displayed. These will be selected by a separate button on the signalman's panel. This is preferred to providing two shunt signals with opposing locking removed as it avoids the possibility of two trains approaching each other both under proceed aspects. 4.7 Trainstops SRA (TfNSW) provides trainstops on most of the Sydney metropolitan area. Double light signalling is normally provided. All electric multiple unit trains are provided with tripcock equipment which will apply the brakes if a train passes a raised trainstop. The trainstops are provided at each main stop signal and in certain other locations (e.g. exits from depots and sidings) to prevent a rear end collision with another train. If the signal is at danger, the trainstop will be raised. A train irregularly passing a signal at danger will be tripped and brought to a stand within the length of the overlap. Where trainstops are to be used, the engineer must ensure that the length of each overlap is adequate for emergency braking at the highest speed at which a train is likely to pass the signal. Obviously the trainstop cannot ensure total safety if all trains are not fitted but it can make a major contribution to safety in areas where trains regularly run at close headways. An important part of the preparation of the signalling plan is therefore to decide where trainstops are to be positioned. This is closely associated with the calculation of overlaps. It may often be more important to accurately position the overlap for track circuit clearance purposes, then work back to the position of the signal and the trainstop. A low speed signal tells the driver that there is little or no overlap beyond the exit signal. Running speeds will be low (normally less than 35km/h). The low speed overlap will be based on the passing speed of the low speed signal. However, the driver could fail to brake, or even accelerate after he has passed the low speed signal. This would leave an inadequate low speed overlap. Intermediate trainstops are therefore often provided between a low speed signal and the next signal, to be lowered only after sufficient time has elapsed for the train to have reached the trainstop at or below the correct speed. The following general rules therefore apply to the positioning of trainstops:- A trainstop is required at all stop signals. It must always be on the same side of the line. SRA (TfNSW) provides trainstops on the left hand side, London Underground and British Rail use the right hand side of the track. Additional trainstops may be required on the approach to stop signals with a reduced overlap where a speed reduction has already been enforced at a previous signal. As an example, a low speed signal reading into a station platform could have a low speed aspect to allow early entry of following trains. The overlap associated with this may be 100 metres or less, even reducing almost to zero. To ensure that a train does not accelerate to a speed which would render the overlap inadequate, an additional trainstop is provided on the approach to the exit signal after the low speed signal. The lowering of this trainstop is timed to trip a train which is running above the permitted speed.  The positioning of trainstops therefore has to take account of the braking and acceleration characteristics of the train and the length of the overlap. The calculation can become very complex so a simple example is used here to illustrate the possibilities. In the following diagram, the two stop signals are 200 metres apart. For headway and/or junction clearance purposes, it has been decided that only a 50 metre overlap is available beyond the second signal. We will assume that the train passes the first signal, displaying a low speed aspect at 27 km/h or less (otherwise it would have been tripped). This example will assume a typical service braking rate of 0.9 m/s 2 , an emergency braking rate of 1.4 m/s 2 and an acceleration rate of 0.55m/s 2 . These are typical of those which have been used for SRA (TfNSW) signalling for electric multiple units although the actual performance of the trains which will use a line must always be confirmed, and gradients taken into consideration. The train should under normal circumstances brake to a stand at signal 2 along or below curve A. The trainstops should ensure that the train will come to a stand within the overlap, should the driver fail to take the correct action to control his train. There are various possibilities which may arise. The signal engineer must decide whether to allow fully for all of these or whether circumstances will permit some relaxation. After passing signal 1 at the permitted speed (27 km/h in this example) the driver could totally fail to brake. Even worse, he could accelerate after passing signal 1. We could assume either no acceleration, acceleration due to gradient only or acceleration under full power. Whichever is chosen, the overlap should be greater than the emergency braking distance from signal 2. If this is not the case, an intermediate trainstop (labelled ITS) must be provided which should be timed to lower just before the train reaches it on a normal service braking curve (point X on the diagram). Curve D shows the effect of this trainstop on a train accelerating under full power. With the intermediate trainstop having been passed at the correct speed (lowered before the arrival of the train), the train could then accelerate at full power towards signal 2. In this case the trainstop at the signal will ensure the train stops within the overlap. Curve B shows the likely speed profile of the train in this situation. Even with these safeguards it is possible that a train could stand just past signal 1 on the timing track circuit for the intermediate trainstop. The trainstop would lower after the prescribed time interval and the train could then accelerate under full power towards signal 2 without the protection of the intermediate trainstop. It will be seen from curve C that the train will overshoot the overlap, passing the overlap joint at up to 9 m/s. To overcome this, the length of the timing track circuit for the intermediate trainstop must be limited such that an accelerating train could pass signal 2 at a speed no higher than that possible on curve B. Alternatively, an additional intermediate trainstop could be provided to check the train speed at an earlier point. SRA (TfNSW) practice in open (i.e. above ground) areas is to allow some margin for possible acceleration but not the deliberate full acceleration of curve C. In tunnel sections where the driver's perception of speed and distance may be affected, the positioning of trainstops and their associated timing track circuits should cater for all possibilities. It should be noted that due to the introduction of newer trains with better acceleration characteristics, the protection provided by certain older sections of signalling is now reduced. It will still protect against most normal occurences other than the deliberately malicious driver intent on overriding the protection of the signalling equipment. Typical distances for open areas are as follows:- For following trains and overlaps less than 50 metres, the intermediate trainstop is positioned 100 metres from the end of the overlap with a timing track circuit between 80 and 220 metres in length. For overlaps clear of fouling movements, the overlap should be at least 100 metres and the intermediate trainstop 200 metres from the fouling point. In addition, any previous signal whose full overlap extends beyond the fouling point should be conditionally cleared to caution. This arrangement is not recommended where signal spacing exceeds 500 metres. TO BE CONTINUED - SIGNALLING BOOK | CHAPTER 3 | PART 3...........

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Deepu Dharmarajan -
Posted 118 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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Esat Kepenekli -
Posted 128 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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Sascha Otto -
Posted 137 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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