How to set Power Swing blocking relay ?
Power swing blocking : From power system operation point of view it is not desirable to obtain tripping from a distance relay during a power swing. The fluctuations of voltage and current occuring in such a case can make it impossible for the relay to discriminate between a 3 phase fault and a heavy power swing. Detection of power swing is made by measuring the time that elapses between the operation of the two concentric impedance elements. The output from the impedance elements is fed to a logic circuit where it is determined whether it is a power swing or a fault that has occured on the network. This is done by considering the fact that the change in apparent impedance during power swing is very slow compared to the sudden change when a fault occurs. The time interval used in the power swing blocking element is 35-40 ms which means that if a change in apparent impedance is larger than this fixed time the power swing blocking element will block the operation of the distance relay for
