Computer Based Interlocking: A New Era In Bangladesh Railway Signaling System. H. M.Ahsan 1, P. K. Biswas 2

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1 Paper ID: TE International Conference on Recent Innovation in Civil Engineering for Sustainable Development () Department of Civil Engineering DUET - Gazipur, Bangladesh Computer Based Interlocking: A New Era In Bangladesh Railway Signaling System H. M.Ahsan 1, P. K. Biswas 2 Abstract Signalling system is the indispensable tool of railway traffic management and regulation system. The railway signalling is governed by a concept called Interlocking. Three types of interlocking systems are widely used in Bangladesh Railway (BR): Mechanical Interlocking, Relay Interlocking and Computer Based Interlocking. In this paper the locations of different interlocking systems in BR, different aspects of CBI, advantages of CBI and signal modernization of BR is described. CBI is a device controlling site signalling equipment by computerizing the electrical and mechanical mechanisms of existing interlocking device. CBI is preferred in BR because of its simple lightweight structure, failsafe configuration, high speed processing of data and simplicity in changing hardware and software. Another major advantage of CBI is the system can automatically diagnose malfunctions and provide alarm indications and error reports to enable signal maintainers to carry out all the requirements for first line maintenance, fault finding and rectification. At present in BR 47 stations have CBI, 61 stations have relay interlocking, 97 stations have mechanical interlocking, 71 stations have non interlocked colour light signalling system and 53 stations have non interlocked mechanical signalling system. BR is planning to modernize the total signalling system into CBI. Keywords: Bangladesh Railway, Signalling System, Computer Based Interlocking, Failsafe Operation 1. Introduction Railway signalling is the most important part of the railway traffic movement for its safety, uninterrupted and smooth flow of traffic. The signal systems ensure avoid collisions and protected against fatalities and property damages. The railway signalling is governed by a concept called Interlocking. Interlocking is a device or system meant for safe working of trains. With the increase in the number of points and signals and introduction of high speeds it has become necessary to eliminate the human error. The setting of points and signals is so arranged that the cabin man cannot lower the signal for reception of a train unless the corresponding points are set and locked. The signal is thus interlocked with the points in a way that no conflicting movement is possible and safety of train is ensured. There are four types of interlocking [1], [2] such as mechanical interlocking, electro mechanical interlocking, relay interlocking and computer based interlocking. The objective of the paper is to determine the modernization trend of signaling system of Bangladesh Railway. Recently Computer Based Interlocking is introduced to Bangladesh Railway as a new era in the signaling system by reduction of number of levers and relays and providing failsafe configuration. 1.1 The Bangladesh Railway Bangladesh Railway is a Government owned and Government managed transportation agency of the country. In 1972, Pakistan Eastern Railway was renamed as Bangladesh Railway after emergence of Bangladesh as sovereign state and continued to function under a railway board. It covers a length of 2,877 route kilometers managed by 25,939 regular staff. At the end of , Bangladesh Railway [3] had a total of 444 number stations, 230 in the Eastern Zone and 214 in the Western Zone, spread over route kilometers of tracks consisting of three gauges viz. Broad 1 Professor, Department of Civil Engineering, BUET, hmahsan@ce.buet.ac.bd 2 Undergraduate Student, Department of Civil Engineering, BUET, pronab04@gmail.com

2 758 gauge (1676mm) of kilometers in the West Zone only, Metre gauge (1000mm) of kilometers and kilometers in the East Zone and in the West Zone respectively and Dual gauge (broad and metre gauges mixed on the same line) of kilometers and kilometers in the East Zone and in the West Zone respectively. In , it owned a fleet of 258 locomotives, 1472 passenger carriages, 33 other coaching vehicles and 9879 units of freight wagons. To meet the growing traffic needs of a developing economy is not an easy task. To ensure both safety and swift movement of increasing traffic need for modernization of signalling system was therefore felt for sometimes. To achieve this modernization, Centralized Traffic Control and Computer Based Interlocking are in implementing stage in Bangladesh Railway. 2. Interlocking Systems Used In Bangladesh Railway Three types of interlocking systems are widely used in Bangladesh Railway [4]. They are discussed in the following section and shown in Fig.1 and Table Mechanical Interlocking In mechanical interlocking mechanical lever frame controls the points with the signals governing that section of track and connected branches, loops, or sidings. Two types of mechanical interlocking used in Bangladesh Railway: Double Wire Mechanical Interlocking and Single Wire Mechanical Interlocking. But mechanical interlocking system is slowly becoming obsolete in Bangladesh Railway as they are very expensive and difficult to maintain because of large number of levers. At present 97 stations of Bangladesh Railway [3] have Mechanical Interlocking. 2.2 Relay Interlocking Relay interlocking system is widely used in Bangladesh Railway. In relay interlocking, interlocking between signals, shunting indicators and point machines are implemented by relay, an electrically operated switch. These relay based circuit implement all types of logic and take inputs from signals, points, track circuit etc. Though it is widely used throughout the world with at the development of information technology, the relay based technology is slowly being phased out and replaced with CBI. At present 61 stations of Bangladesh Railway [3] have Relay Interlocking. 2.3 Computer Based Interlocking Computer Based Interlocking (CBI) [4], [5] is a device controlling site signalling equipment by computerizing the electric and mechanical mechanisms of existing interlocking devices. The interlocking function is operated by computer software. The same Interlocking rules or control equations used in Relay Interlocking form the basis here also. There are [4] two types of CBI: centralized type and distributed type. At present 47 stations of Bangladesh Railway [3] have Computer Based Interlocking. 2.4 Non Interlocked Stations Besides these three types of interlocking systems 124 stations [3] have no interlocking system because the number of trains passing through these stations are relatively low and traffic management is easier. Among the non interlocked stations, 71 stations have colour light signalling system and 53 stations have mechanical signalling system..

3 759 Fig 1: Bangladesh Railway Route Map with Interlocking Systems

4 760 Table 1: Interlocking Systems in Different Railway Stations in Bangladesh Type of Block Equipment No. of Stations Computer Based Interlocking 47 Relay Interlocking 61 Double wire Mechanical Interlocked 47 Single Wire Mechanical Interlocked 50 Non Interlocked Colour Light 71 Non Interlocked Mechanical Introducing Computer Based Interlocking in Bangladesh Railway There are [4] two types of CBI: centralized type and distributed type. The centralized type is configured in such a manner that all the relays, electronic cards or modules are installed at a Signal Equipment Room. The distributed type controls site signalling equipment remotely by using relays, electronic cards or modules at an enclosure adjacent to a starting signal or a home signal. Distributed type CBI is being used in Bangladesh Railway. Bangladesh Railway has introduced Computer Based Interlocking system at 7 stations from Joydebpur to Bongabandhu Bridge west and at another 7 stations from Jamtail to Muladuli. CBI has also been introduced at 23 stations in Akhauara-Sylhet section and at 6 stations in Dhaka-Joydebpur section and 4 stations in West Zone such as Santahar, Abdulpur, Azimnagar and Ishurdi by pass. Moreover modernization of signalling and interlock system of 13 stations from Bhawal Gajipur to Mymensingh is under construction and that of 11 stations from Chittagong Junction cabin to Chinky Astana is under pipeline. 3.1 Reasons for Introducing CBI in BR Relay interlocking was proved more economical and less complex than Mechanical interlocking and hence was used widely. But with the introduction of CBI Relay interlocking is slowly being phased out. CBI has a lot of advantages such as: Approximately 60% reduction in relay used. 50% reduction in space required. 30% reduction in power consumption. Less manpower requirement for traffic management during blocks as well as less detention to trains. Reduction in wiring and interconnections. No relays are required for interlocking function. Only interface relays are required. Reduction in number of fuses. Less time required for installation. Easy maintenance of system. More reliability due to less relays and accessories. CBI has got self-diagnostic features. Any failure in the system is located and enunciated. Faulty module can be immediately replaced by spare module hence the down time of installation is reduced.

5 761 Less prone to short cut method, total system goes to shut down if point/ signal is even wrong feed. The conventional block and intermediate Block system circuit can be incorporated in the CBI system circuitry. Less possibility of wiring fault. Any change to the station yard can be quickly addressed by changing the lookup tables and can virtually be done in a matter of hours. Though CBI has a lot of advantages and failsafe feature it can be non reliable for the following reasons: Every railway zone has its own set of rules and principles which are conflicting with other railways. This lack of standardization of interlocking principles makes the life of the developers difficult because they have change their systems settings and software accordingly. Since the software and hardware is so complex, complete test of the system is not possible and most of the faults are revealed at the field Installation stage or during normal working of the system in field. The software developers are forced to do changes in the software for every station in Different railway zones, this is the time that errors in the software occurs. There is no standard book or reference available describing the core interlocking principles, since these rules are only known by the people working in that particular region. 3.2 Failsafe Feature of CBI The CBI system is designed on fail safe principles. In case of any failure whether in the hardware, software or any part of the equipment, the system and the equipments controlled by fails on safe side and the system change over to a more restrictive state. Any single failure results in an unsafe condition then the system changes to a safe state as soon as failure occurs. The design of the equipment is cater for detection and restoration of system to a safer state in case of following faults : Variation in power supply beyond its tolerance limits, including momentary failure of the power supply system. Spikes in the power supply system, stray fields caused by traction vehicles or standby diesel generator sets. Insertion of Printed Circuit Boards (PCB) in wrong card slots Earthing of any component of wire or a combination of such earthing faults. Broken wires, damaged or dirty contacts failure of a component to energize loss of power supply or blown fuse etc. 4. Interlocking Methodology in CBI Two types of methods are applied in software for interlocking in CBI: 4.1 Geographical Method In the geographical method the input to the CBI is given as the positions of the signals, points, track circuits and slots. Patalay [6] said that the Interlocking is implemented based on the generic rules that no part of the track are shared by the two routes at a time, conflicting routes should not be set at a time etc. This type of implementation requires a great knowledge of the Yard Elements and the interconnection between them. In this method the software does not have one to one relationship to the relay circuits that are used for Relay Interlocking. As a result this method is very difficult validate and has failed to create the necessary confidence in the railway operator.

6 Boolean Equation Method The Boolean equation method [7] is the implementation of the traditional relay interlocking principles. In this method the relay circuits are implemented as Boolean equations [6] and there is one to one relationship between the relay circuits and the software variables. Since there is a one to one relationship between the software and the Relay circuits, Railway operator can easily validate the software entrees made and this method will give him sufficient confidence. 5. Conclusion The introduction of Computer Based Interlocking in signalling system in Bangladesh is helping to ensure safety and makes the signaling system a easy and convenient one. It is suggested that in the complex field of Railway Signalling, where safety, availability and maintainability are the prime issues, Computer Based Interlocking should be introduced. Bangladesh Railway is planning to modernize the total signalling system into Computer Based Interlocking. When this is done the signalling system will be capable of providing every degree of protection required for traffic. 6. References [1] Rangawala, S.C. Principles of Railway Engineering, 15 th ed., Tata & Mc Grow Hill, pp- 317, [2] Wikipedia, Interlocking, (June 18, 2015). [3] Information Book, 2013, Bangladesh Railway. [4] Korea Exim Bank, Feasibility Study on Replacement and Modernization of the Existing Railway Signalling System at 25 stations of Bangladesh, pp 35-37, [5] Wikipedia, Computer Based Interlocking, Interlocking (June 22, 2015). [6] Patalay S., Analysis of Railway interlocking systems, /Analysis-Of-Computer-Based-Interlocking, (June 21, 2015). [7] Srivastav V., Notes on Solid State Interlocking, (June 22, 2015).

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