A new power swing blocking function based on wavelet transform

Power swing blocking function is necessary to distance relays 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 is straightforward in the case of asymmetrical faults by using zero- and negative-sequence detection functions, detecting symmetrical faults during a power swing still presents a challenge. This paper utilizes wavelet transform (WT) to propose a new method which can be used in distance relays for power swing blocking function. The proposed method performs WT on impedance magnitude to detect power swing and any fault occurring during the phenomenon. The wavelet coefficients of the dyadic levels that will be used to detect power swings and faults are perfectly presented. Power swings and faults are simulated by using PSCAD/EMTDC^®, and WT is performed by wavelet toolbox of MATLAB^®.