Reconstitution of power transformer's residual flux with CVT's measurement during its de-energization

Abstract

Power transformer's de-energization leaves the transformer core in a state of magnetization, called residual flux. The presence of this residual flux may induce inrush current which can cause damages on the equipments and system disturbances. In recent years, studies on power transformer's controlled switching have been carried out to reduce this effect. The purpose of this paper is to emphasize the calculation of residual flux with CVT (Capacitive Voltage Transformer) measurement, using EMTP, during the de-energization of no loaded power transformer. Measuring and integrating directly the CVT's voltage output may provide a false flux value.