Protection of parallel multi-circuit transmission lines

This paper presents the principle of a new protection method for parallel multicircuit transmission lines. Owing to the zero-phase circulating current emerging in parallel multicircuit transmission lines frequently leads conventional ground protection relays to the malfunction in the high resistance neutral-grounding system. A new protective method for the zero-phase circulating current based on the principle of matrix operation type protection relay is proposed through introducing the circulating electromotive force as a system variable that drives the zero-phase circulating current in the parallel multicircuit. The accuracy of the new protection relay is quite high for detecting fault location in simulation tests. The algorithm of the new protection scheme is illustrated in detail in this paper.