Askarian - Amir Kabir Univ. IRAN
Mohseni - Tehran Univ. IRAN
Azarnoosh - GREC IRAN

Current transformer core may be saturated by heavy short circuit current. To analyses saturation digital computer is needed. Component with low frequency has most important role. It is necessary to calculate transient and subtransient and DC componet first and used as input of saturation program. Core reluctance variation remanant flux density, hystersis and eddy losses are considered. In this paper a computer program is developed in which computation of dynamic current plus protective current transformer are included. Typical results for C. T's installed on 230 KV Iran network are given.