Hybrid overcurrent protection relay based on rotating magnetic field principle

This paper presents a novel hybrid power system overcurrent protection relay based on rotating magnetic field principle. The device is directly connected into the regular current transformer (CT) secondary circuit and consists of an electromagnetic component with rotating magnetic field and an electronics circuit employed to generate a low-level analog output, which is directly proportional to the magnitude of the input current signal. The relay output is produced without using numerical signal algorithms by the hybrid physical system. Moreover, the relay provides galvanic isolation from the secondary CT circuit and is capable of auto-correcting the input current waveform distortions introduced by CT saturation.