Methods for estimating transient performance of practical current transformers for relaying

Abstract

Since engineers learned, about 50 years ago, that a current transformer has real difficulty with an initially fully offset transient current, they have written many papers about the difficulty without finding a solution for most practical relay problems. This paper offers new data and methods which are intended to lead the relay engineer to solutions to many problems and to give him a better insight toward proper action in cases where there is still no simple solution. The emphasis is on practical problem solving. Some of the assumptions which are made can be defended on the basis that the solution, however much in error, errs on the safe side, and that the solution is a most valuable guide to the relay engineer.