Demagnetization of Current Transformers Using PWM Burden

Current transformers (CTs) show large errors when they are magnetized by dc current. This error can be reduced after proper demagnetization. One of the methods to demagnetize the CT is to increase the core flux by increasing its burden. The burden should be adjusted according to the measured ac current. In this paper, we show that pulsewidth modulation switchable resistor can be used as variable burden for this application. This method enables to restore the nominal precision of the heavily magnetized CT from 2.5% back to 0.2% without interruption of the CT operation.