Symmetrical Fault—Swing Discrimination Using RMS Index-Based Superimposed Current Signals
To maintain reliable and secured power system operation, relays are designed to operate at a faster rate so as to provide an appropriate tripping signal to circuit breakers under any abnormal transient condition. During swing phenomenon, operation of a relay is required to block with the help of PSB function so that any nuisance operation can be avoided. Unblocking operation can easily be issued by the relay in case of an unsymmetrical fault, but detection of symmetrical fault is a difficult task. A novel approach to discriminate three-phase fault from power swing using the root mean square (RMS) value of superimposed current signal is proposed in this paper. Superimposed current signal is estimated by taking the difference between two consecutive cycles considering the recursive window approach. The index is then computed by estimating the RMS value from the one-cycle superimposed current components. The generated index helps the relay to discriminate symmetrical fault from power swing. To verify the response of proposed method, a 400 kV, 50 Hz WSCC 9-bus test system is considered and simulated with different fault cases. The power system model is simulated using PSCAD/EMTDC software, and results indicate the robustness of the proposed algorithm.
KeywordsTransmission lines Superimposed current components RMS index Power swing Symmetrical faults
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