Reliability issues of metal to carbon relays used in railway signaling

Abstract

Metal to Carbon Relays are used in railway signaling for operating various signaling functions viz. signals/points/track circuits etc. These relays consist of a metal (Silver) contact and a Carbon (Silver Impregnated Graphite) contact, which make and break as per the signaling logic and switch on the current to the signaling equipment. The reliability of these relays is very poor. One major reason of poor reliability is the high contact resistance developed in the SIG contacts, due to which the relay stops picking up and fails. Failure of these relays causes disruption to train operations and adversely affects the train punctuality. It may also result in unsafe situation for train traffic. The quality of metal to carbon relays needs to be enhanced so as to ensure safe train operations and to alleviate passenger grievances caused due to frequent disruptions in train operations.