Dynamic model of a current transformer

The performance of current transformers and its errors during short-circuit conditions are very important with regard to protective devices in power networks. Core saturation of protective current transformers due to the d.c. component of fault current and the qualitative effect of core hysteresis resulting in residual flux are both well-known phenomena which can produce distorted output currents. A numerical technique for the mathematical representation of the flux density/field strength relationship, including the effects of hysteresis for a current transformer magnetic material, is presented, based on the use of exponential series. The simulation results are compared with experimental results obtained from a sample current transformer.