Theory and Design of Premagnetized Current Transformers

The great simplicity, reliability, and low cost of the bushing-type current transformer has led inventors to devise various schemes to improve its accuracy to metering standards. Premagnetization is one of such methods. When premagnetized by an auxiliary core it has the added advantage that it does not need any external source of power supply. This method, however, has been little used in practice, because its theory was never properly understood. The present paper develops the theory of a method for calculating performance and also gives a comprehensive design procedure for such a current transformer.