On the Coordination of Current Transformers and Relay Protection and Automation Operation of Electric-Power Systems in Transient Short-Circuit States

Due to the increasing number of incorrect actions of relay protection in transient processes accompanied by saturation of current-transformer (CT) cores, there is a need for developing a domestic standard for protective CTs designed to operate in transient states. The following ways to provide proper relay protection operation in transient states accompanied by saturation of CTs in operation are considered: (a) CT shedding that includes an increase in control cables’ cross sections, (b) development of relay-protection and automation algorithms based on the recognition of crash conditions in an appropriate CT transformation time interval of 2–3 ms, (c) development of relay-protection and automation algorithms with virtual CT error compensation, and (d) development and introduction of new primary-current converters. It is concluded that, for existing large power plants with installed TPX current transformers, it is advisable to use improved digital relay-protection algorithms for information processing obtained from CTs, for example, by methods (b) and/or (c).