Circuit Breaker and Protection Requirements for DC Switchgear used in Rapid Transit Systems

Attention is drawn to the interrupting severities encountered by dc circuit breakers on rapid transit systems and how specifications can more clearly define these conditions. The various protection equipment requirements are discussed, and it is shown that one of these requirements is difficult because of the similarity which can exist between healthy and abnormal conditions, making discrimination under certain conditions, almost impossible. A guide is given to the minimum requirements for the de switchgear which should ensure a reliable and secure power supply to the rapid transit system.