A New Power Swing Blocking Function Based on Wavelet Transform

Power swing blocking function in distance relays is necessary to distinguish between a power swing and a fault. However the distance relay should be fast and reliably unblocked if any fault occurs during a power swing. Although unblocking the relay under asymmetrical fault conditions is evident and straightforward based on zero-sequence detection function but symmetrical fault detection during a power swing presents a challenge. This paper utilizes wavelet transform to reliably and quickly detect power swing as well as detect any fault occurring during a power swing. The impedance magnitude waveform used for the power swing blocking function is carefully studied through analytical calculations as well as simulation results. The proper dyadic level associated with the wavelet transform of impedance magnitude used to detect both power swing and fault is shown based on a common presentation of wavelet transform called as a detail. A power swing is simulated by using PSCAD/EMTDC® software and wavelet transform is performed by wavelet toolbox of MATLAB® software.