New insights into the distance relaying problems caused by CVTs have been given. As explained, various CVT configurations (value of the stack capacitances, type of the ferroresonance circuit and amount of load) affect the relay performance to a different degree. Transient overreach specifications of relays available on the market are very imprecise. Definition of transient overreach and test conditions (type of a CVT, primarily) are not specified by the vendors. This relates to type of a CVT, type of a ferroresonance circuit, CVT burden, fault inception angle, etc. Tests performed by the authors on selected relays using the CVT-1 and CVT-2 models delivered much worse performance characteristics than those published by vendors. In many instances comparatively short operating time independent from the fault location is a sign of a very poor CVT transient control under high SIRs. In response to that, a new algorithm has been presented in this paper that ensures superior performance in terms of transient overreach without significant sacrificing the speed of operation.
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