An Adaptive Algorithm for Fault Identification in Transmission Lines by Short-Time Fourier Transform Function

Transmission lines are protected by distance relays as main protection and overcurrent relays as backup protection. Both of distance relays and overcurrent relays have mal-operation during high Impedance faults, faults in the week in-feed systems and faults occurred during power swing. Fluctuations in voltage and current during power swing cause fluctuations in measured impedance by distance relay. In some measured impedance moves to protected zone and causes mal-operation. So, distance relay is blocked duration of a power swing. In cases that fault occurs during a power swing, the relay must detect fault inception. In this paper, a new algorithm for fault detection in cases with low fault current and fault detection during power swing is presented. Diagnostic criteria in this algorithm are the calculation of the spectral energy of current signal by the Adaptive Short-Time Fourier transform (ASTFT). Fault currents consist of a considerable amount of high-frequency components which they do not exist the in-line current during overload or power swing. The presented method is based on cooperation between existing fault detection methods and a fault detection using ASTST. Different conditions are Simulated in this paper in the software / EMTDC PSCAD and MATLAB to verify of correct performance of the proposed algorithm.