A novel algorithm to detect symmetrical faults during power swing for a double circuit multi-terminal transmission line

Mal-operation of distance relays due to power swing has resulted in the development of several power swing blocking algorithms. A blinded distance relay is incapable of issuing trip signal in case faults occur during power swing. Detection of three phase faults during power swing imposes a challenge, owing to the symmetrical nature of both the power swing and three phase faults. This paper proposes a novel yet simple algorithm to detect symmetrical faults during power swing on a double circuit multi-terminal line; which performs reliably under changing system impedance, varying power swing slip frequency, infeed effect; and is computationally efficient. The current signals during power swing will have amplitude modulation governed by the slip frequency. Thus, the rate of change of current magnitude phasor will be non zero. During three phase faults, if the dc offset from current waveform is eliminated, the fault current will consists of only steady state ac sinusoidal response. Thus, during three phase faults, the rate of change of current magnitude phasor will be zero. For enhancing the security of the scheme, the sign of sine of the current angle is also monitored. The scheme is implemented on the Alternative Transient Program environment and the rigorous simulations performed show the reliability of the scheme.