Symmetrical Fault Detection During Power Swing Based on dq-Wavelet Packet Entropy

Distance relay trips unnecessarily under power swing condition and it is considered as the significant circumstance for power system blackouts. To prevent the hazard of misoperation of distance relay, a scheme is essential so as to block circuit breaker tripping during power swing and to detect a fault during power swing condition. In Power system faults, unsymmetrical faults are unbalanced signals which have negative & zero sequence components, and these sequence components help to identify the faults during the power swing. Whereas, these components are absent during symmetrical fault since power swing and symmetrical fault are balanced phenomena. Symmetrical fault detection under power swing condition is a critical issue. Hence, Power system protection due to symmetrical fault during power swing is difficult. In this regard, a proposed scheme based on Direct axis - Quadrature axis transformation and Wavelet packet entropy to identify symmetrical faults occurring with power swing is proposed. The proposed technique is investigated for various power swing and fault conditions on two-machine system, distribution system with distributed generation and WSCC 9-bus system using Matlab software. This scheme provides better results irrespective of various fault locations, fault inception angle, and power swing frequencies. This scheme can also detect asymmetrical faults with high impedance during power swing.