Determination of an Accurate Current Transformer Model for the Analysis of Electromagnetic Transient During Electrical Faults

It is necessary to predict the performance of a current transformer under transient conditions for appropriate protection. When a short circuit fault in the power system occurs، the current transformer approaches to saturation region and will be led to the secondary current distortion. Hence، it affects the protective relays operation and as a result، maloperation will occur for the protective relays. Thus، it needs an accurate model of current transformer under short circuit in order to analyze the protective relays operation. In this paper، An Accurate mathematical model is developed for a current transformer to predict the transient performance with a complex burden consisting of inductance and resistance، taking core saturation into account. A typical 1200/5 A current transformer will be simulated with various maximum offset fault currents. The secondary current and flux response will be computed for different values of burden impedance. To validate the method a comparison is made with ATP-EMTP time domain simulation program and with IEEE power system relaying committee current transformer model. The results give excellent agreement with the time domain simulation and IEEE model.