New power swing blocking method

Prior to the power swing conditions, the power angle is small and the operating point lies in a load impedance area on the extreme right of the complex plane. When loss of synchronism takes place, the angle increases and the impedance locus moves along an impedance circle with possible encroachment into the distance relay zone. This may cause an unnecessary tripping. In order to avoid such a situation the distance protection schemes have an optional power swing blocking relay which should reliably detect a power swing and block the distance relay. There are two main blocking methods, each of them having some advantages and disadvantages. In this paper a possible modification of one of these blocking methods is described.