Zero-sequence current blocking device for two phase AC systems

Resonantly grounded power systems require fault current limitation in order to meet current standards and to ensure personal safety. A current limiting transformer (CLT), based on an isolating transformer, is investigated here. The major advantages of a CLT, compared to an isolating transformer, are power derating, reduction of leakage reactance and thus reduced losses and reactive power demand during operation. MATLAB/Simulink® is used to investigate the electrical behavior of the CLT. Simulations of a phase-to-ground fault are made to proof the reduction of fault currents. Modelling the CLT in symmetric components demonstrates the blocking mechanism for the zero-sequence currents. In this context special attention has to be paid to resonant currents in resonantly grounded networks, when using the CLT.