TRANSIENTS IN THE CURRENT CIRCUITS OF HIGH-SPEED PROTECTIONS OF THE MAIN EQUIPMENT OF POWER STATIONS UNDER CONDITIONS OF SEQUENTIAL SHORT-CIRCUIT FAULTS

摘要

A method of identifying the conditions for extreme spurious signals to occur due to the interaction of current transformers (CT) arranged in three-phase groups when sequential phase-to-ground short-circuit faults occur, is proposed. The method enables the currents in the healthy phases to be taken into account and enables the influence of sequential switching operations on the aperiodic component of the primary and secondary currents to be considered. A maximum aperiodic component can develop when a double sequential short-circuit fault, that is, a single-phase fault - two-phase ground fault - three-phase short-circuit fault, occurs. An extreme distortion of the secondary current of a saturated CT may occur when there is a sequential short-circuit fault and when the CT in the healthy phase in the group of CTs connected in a star become saturated as a result of an excessive zero-sequence current, which is typical for the high-voltage equipment of power stations.