Ferensovych R. Operation Modes and Protection of Current Transformers after Disconnection of Secondary Circuits

The thesis deals with an analysis of operation modes of current transformers after the emergency disconnection of their secondary circuits and a designing of a protection system of current transformers against overvoltages in such modes. The calculation schemes with taking into account losses of active power in the magnetic cores of current transformers are developed and the values of overvoltages on their secondary terminals are calculated. The method of estimation of the maximum amplitudes of overvoltages on the terminals of current transformer secondary winding after disconnection its secondary circuit, when sinusoid current flows in the primary winding, is proposed. In the thesis the protection system against overvoltages after disconnection of secondary circuits of current transformers is proposed, the basic requirements for this system are considered. The efficiency of protection system operation and a limitation of secondary overvoltages to the admissible values are confirmed by using experiments and computer simulation of operation modes of protection system.