A microprocessor based bus relay using a current transformer saturation detector

A microprocessor based bus protection scheme is presented. It uses a novel technique to overcome the problem of current transformer saturation. The protection algorithm uses a combination of the percentage differential principles and the phase comparison technique. With a sampling rate of 1440 Hz (24 samples/cycle on a 60 Hz system) a realistic bus is considered for algorithm testing. With the incorporation of this saturation detector, the relay can yield a correct trip/block decision for either an internal or an external fault in the presence of current transformer saturation within one cycle. In the best case, this protection scheme can give a trip/block decision in a quarter cycle. Simulation results show that the saturation detection algorithm and the hybrid bus protection algorithm (using percentage differential and phase comparison principles) are simple, efficient, and accurate