Research on Unloaded Switching Into Fault Protection for UHV Transmission Line

The rapidity of conventional switching into fault (SIF) protection is decelerated greatly because of the serious transient of unloaded switching in ultra high voltage (UHV) or extra high voltage (EHV) transmission line. Theoretical analysis shows that the impedance angles measured between switching into normal and fault state are different. Based on the comparison of the harmonic noise level under these conditions, a novel scheme of unloaded SIF protection with an assistant speedy distance relay is put forward in this paper. Analysis and mass EMTP simulation show that the scheme can distinguish fault state from normal line quickly and accurately. Accordingly it possesses a good engineering application prospect for its sensitivity and rapidity.