Electromagnetic Compatibility: Railway Signalling System - Term Paper Example

Report by ashok kaul EMC=ELECTROMAGNETIC COMPATIBILITY Railway Signalling System The ability of electronic apparatus to operate in the surrounding environment, without causing any degradation or any suffering to the working of other apparatus is called Electromagnetic Compatibility In January 1996, European EMC issued a directive—89/336/EEC. This directive gives the requirement of control of EMC in all spheres, as it applies to all electrical and electronic devices, operating in major projects which include the Railways as well.. EMC on the face of it may not be specifically safety related, but it certainly forms the important part of safety regulations for all the railway systems .Under the EMC directive, there are series of standards that are applicable for the railway systems only. While EN 50121 is the main standard laid for the railways, there are subgroups of this standard that cater to various aspects of the railways operation. EN 50121 – 4 is the specific standard that applies to the Emission and Immunity of Railway signaling and telecommunication devices. EMC Management An EMC management plan is sometimes also called as an EMC test plan. With such a plan, the EMC management is always possible. The EMC test plan usually will include the following. Which EMC test is required? Is there any possible and justifiable reason to deviate from the EMC standards? Equipment configuration and its operational mode. The criteria for the immunity performance. The EMC test report should include the following: Full details of the equipment tested Full description of EMC testing performed on the equipment and the results obtained. Detailed observation of any modification done on the equipment to make it EMC compatible Railway signaling system In any railway system, it is essential that the traffic move smoothly, and safely. The railway signalling system is essentially a program to ensure this. The need for such a system was felt to avoid the collision of the trains at any point in the route, while many trains operate on a particular route. Starting from the early days the rail signalling was known as Block signalling, which meant blocking of the train on a certain route to let the other train pass. .For this purpose the railway lines are divided into blocks so that only one train can pass through the block at a particular time However later on, fixed signals were erected on the poles located near the tracks to indicate the movement of trains. These signals being still in use have different colors to indicate the advice to the train driver for proceeding, stopping or waiting for some time. Further, mechanical signals were installed which reduces the work for most of the gang men on the rail route. The modern railway signalling system will require computerized operations, while having the proper synchronization of software and hardware to ensure the safety of the railway system, as per the standards laid out. .The required signalling system has to be quite robust and above all, it must have the electromagnetic compatibility with the other apparatus and equipment working in the rail system as such, whether on board or along the route. The signalling system must be immune to the surrounding electronic or electrical devices operating within the railway system, so that it does not cause any harm or impair the functionality of these devices in any manner. Railway Signalling System requirements. The requirements of any project for railway signaling system will broadly include the following: Scheme plan preparation that will include inspection of the site and the entire route; finalizing of project specification and signaling equipment design specification. Details of the signaling designs;, control cables and the input/output circuits. Level crossing designs and designs of Mechanical and relay based interlocking devices. Signal sighting and data preparation. Testing plans for the railway signaling system The main standards that apply to testing and design of railway signaling system are broadly given below. EN 50128 / IEC 62279 This refers to Railway Applications - Communications, Signaling And Processing Systems – The Software For Railway Control And Protection Systems are also included in these standards.). EN 50129 (Railway Applications - Communication, Signaling And Processing Systems - Safety Related Electronic Systems For Signaling While the above two standards are mainly responsible for the railways signaling system operation, there are other standards like EN 50126 These standards are responsible for specification and demonstration of reliability, Availability, maintainability and safety (RAMS) of the system.; The following equipment and devices are required for the purpose of testing the design and testing of the railway signaling system. Point machines Level crossing protection systems Track circuits Signals Special signals (topographical and others) Axle counters Cables Rail connections Beacons and synchronization loops Line side signs All types of relays All types of racks Control and-indication panels All types of signaling power supply equipment Computer-based interlocking equipment Lever frame ATP equipment (onboard equipment equipment) Railways signaling system testing will include functional and principal testing, wire counts, co-relation testing, continuity and breakdown tests etc. Software tools required for computerized testing of signaling system will include: Drafting aid required for drawing and design of signaling circuits Deriving from the table of controls(interlocking data), a customized software solution is required for automatic generation of signaling circuits (TOC-SC) A software tool called RCA 1, which is required for analyzing the relay contacts in the circuit diagrams and then converting it to the wiring diagrams. Software for Railway signaling applications The software developed should conform to applicable standards based on CENELEC EN 50128 A core software based on the Motorola MC68XXX processor is designed, and tested on a standard platform. Development of communication stack structured to ISO/OSI standards. An Euro radio communication stack enables communication between the ground devices and on-board within the European Rail Traffic management System ( ERTMS ) Design, development and testing of application software with man-machine interface sub system specification software mounted onboard rolling stock While the languages commonly used for the software writing are ANSI C, C++, Assembler, ADA 83 and ADA 95, the Simulators are designed for testing and system integration functions, for the railway systems. Reverse Engineering Software. All railway systems that are used in applications related to safety etc. must conform to the laid standards of CENELEC. Therefore, it is required to go for reverse engineering activities, mainly to reconstruct system from the written code so that application meets the required detailed parameters of the documented standards, related to the architectural design and other software development etc. The software written documents must conform to the specific Safety Integrity Levels (SIL). Integration of hardware and software and its testing The software has to be tested and verified, as per the applicable standards EN 50128 and EN 50126.The software developed has to meet the particular requirements of a phase of the signaling system and it may not be same for all the phases. Therefore, the software should be developed correctly keeping in view such requirements. In addition, the interaction of software and hardware must be checked so that they function in a proper and coordinated manner. Hence, a software verification and testing plan has to be in place. While Safety Integrity Level standards require that the test and verification should be carried out by a team independent of the developers of the software, a verification report is needed which states that the software has passed the required tests.. The following tests are mainly carried out for this purpose. Module tests These tests are required to check the detailed design parameters. These tests are done on the host as well as target computer. The tools used for this test include Cantata (IPL) tools for module tests. Software Integration tests Such tests are conducted to verify the software architecture requirements. While, for this purpose, Black Box approaches are employed, these tests must be prepared on the host computer and they should be executed on the target computer. Hardware/Software Integration tests The interaction of software with the corresponding hardware is verified by these tests to check the parameters as per the architectural requirements. Here again, the Black box, Equivalence class or Manual inspection methods are used. The hardware/software integration test plan and its reports should conform to the set applicable standards, mainly EN 50128 and EN 50129. Software Validation plan All railway-signaling systems should carry out the software validation activities, that conform to the set standards and CENELEC.The applicable Safety Integrity Levels procedure lays out such software requirement specification that should conform to the functional and safety parameters of the railway signaling system. For this purpose the test analysis is done for the software/ hardware used. Such test activity is generally carried out with the use of simulators that permit the simulation of the real environment, which can be sometimes hostile or inaccessible. While all tests are done on simulators, they should be repeated in the real system execution environment. Following System level safety analysis are required: Preliminary hazard analysis using Hazard and Operability study techniques “Failure Mode Effect and Criticality” ,analysis using Hazard techniques. In addition to this, Fault analysis techniques are also required. Software and System safety assessment Assessment is required for the software development related to the safety systems of the railways signaling applications. This is mainly to ensure that the system is proper for the applicable safety standards meant for the design and construction of railway apparatus. All aspects related to the quality and safety management are evaluated under this program. Functional assessment of railway systems All systems that support the railway signaling are basically originated as ‘Generic application”. However, they become the “Specific applications” when they are applied for specific condition and configured accordingly. The project application will require broadly these two application systems, which arise out of the system requirement specifications. All the test specification must also meet the standards of new signaling systems like Italian ( SCMT, SSC ) and European standards for high speed network ( ERTMS / ETCS ) While there can be many detailed requirements that one needs to look into while designing and testing a railway signalling system, the above points are some of the precise requirements involved in the whole process. The standards laid out need to be strictly followed, along with the safety norms (RAMS ) standards Sources used Indian Railways British railways. , Read More