The use of static shunt compensation to upgrade existing electrified railways

When 25 kV AC railway power supplies are designed, the electrical capacity is arranged to suit future levels of traffic, which are predicted to occur several years after the start of electrified operation. As traffic levels grow, the spare capacity is gradually used up until the load reaches the design limit. Beyond this point operating difficulties can occur, the two main problems being excessive catenary current and low catenary voltage. On a number of railway systems, the design capacity has been reached and various means of increasing the traffic capacity have been investigated. As a consequence, several railway authorities in different parts of the world are considering methods of improving their electrical capacity. Several means of upgrading the power supply system are possible, each with particular advantages and disadvantages. Some of these are considered by the authors