Calculation of the transient performance of protective current transformers including core hysteresis

Core saturation of protective current transformers, due to the DC component of fault current and the qualitative effect of core hysteresis resulting in residual flux are both well known phenomena that can produce distorted output currents. A digital simulation technique, previously described, which represents both hysteresis and eddy-current action in the core steel is used to compute current waveshapes and flux excursions for a wide range of fault current parameters. The production of residual core flux and its influence on secondary current output is also examined