A new method to rapidly identify the symmetrical fault occurring during power swings

Distance protection is required to rapidly block protection when detecting power swings and rapidly unlock protection when the symmetrical fault occurring during power swings. It is difficult to rapidly identify the symmetrical fault during power swings. In this respect, this paper discusses the electrical characteristics of power swings and symmetrical fault during power swings, and brings forward a new method based on U(cos phi ) waveform characteristics to rapidly identify the symmetrical fault during power swings. The paper proves that the difference of U(cos phi ) waveform between power swings and symmetrical fault is clear and adequate resolution can be obtained in a short time, so this method can quickly detect power swings when they occur and block the distance protection. Besides, it can also unblock the distance protection as soon as the symmetrical fault occurs during power swings. This method has a clear physical meaning, simple calculation, short identification delay and no relation with system p