AC electrified railways-protection and distance to fault measurement

This paper examines the variety of infeed arrangements used to optimise the supply of power for AC electrified railways. These feeding arrangements and the increasing use of regenerative locomotive braking present unusual impedances to distance measuring elements and impedance measuring fault locators. The resultant optimisation of the relay impedance characteristic, overcurrent backup protection, and integral fault locator is discussed. Special considerations for low frequency 16.7 Hz and 25 Hz systems are examined. Finally, the gathering and processing of data by the relay, for transmission to a central location, is reviewed