New method of power swing blocking for digital distance protection

A new method for preventing digital distance relay operation during power swings is presented based on detection of transients in the measured reactance. The transients are detected by the difference between two reactances calculated using two parallel FIR filters based on coefficients used in the discrete Hartley transform. The transients are present under genuine fault conditions but not during power swings. Fault transient detection therefore enables the relay for faults but leaves it inherently blocked for power swings. Simulation results are presented showing that the fault transient detection method does not lead to increased relay operating time, but allows the relay to differentiate between faults and power swings. The significant advantage of this new method of blocking is that the relay can correctly operate if a genuine fault occurs during the power swing period