INVESTIGATIONS ON POWER SUPPLY AND SCADA SECURITY ISSUES OF 25 KV AC TRACTION SYSTEM

Abstract

Recently, Need of electrical railways are felt as most preferred mode of public transport because of fossil energy depletion and to prevent global warming due to carbon emission. 25KV AC network is adopted in cities having high traffic or cover long distances. 25 kV AC traction has the economical advantages of less number of traction sub-stations and capacity to carry large traffic and suited for urban cities having passenger capacity of more than a lakh per day. Power supply for 25KV AC traction system is fed to overhead conductors at feeding post location through traction sub-station having 02 transformers in hot/standby configuration. This power supply is used by locomotives with the help of pantograph for current collection. When any problem occurs in the network due to signalling or locomotive failure, there is a tendency of bunching of trains in one feeding section which causes tripping of traction feeder breakers on overcurrent. During such scenario, it should be possible to allow parallel operation of traction transformers with a mechanism to reduce the fault level. Feed from one substation on single phase 25 kV, depending on number of trains and voltage drop, gets limited to 16 to 20 kMs. Therefore, Neutral section is implemented between two different sources to prevent bridging of two different phases. When a train passes through a neutral section, the electrical power supply phase is changed. Before negotiating neutral section, the train must switch off the circuit breaker to avoid transients such as inrush currents and arcs. If train circuit breaker doesn’t open while negotiating healthy section to dead section, there is huge arc due to current break which cause severe damage to overhead components. Also, life of the train circuit breaker owing to its frequent operation is affected. Conventional neutral section has demerits and operational implications which demands to explore new technology to be used in place of neutral section. Fail safe mechanism using Semi-conductor commutated neutral section is analyzed in this report to mitigate these problems when trains pass through the neutral section. An alternate of conventional neutral section and fault level limiter is discussed in this report. Further, SCADA system implemented for control and monitoring of traction system should be well secure to ensure reliable monitoring and safe control of traction devices. Vulnerability assessment of traction system and remedies are discussed in this report. This thesis investigates aspects of semi-conductor based neutral section, Superconducting fault current limiter and its security aspects of SCADA system for a 25KV AC traction system.