Study on Phase Comparison Pilot Protection for Six-Phase Transmission Lines Based on Six-Sequence Transformation

Abstract

Six-phase transmission system occupys a narrow line corridor, and it can also effectively improve power transmission density, so it gains more and more attention. A new scheme of phase comparison protection suitable for six-phase transmission lines was proposed in this paper. Because both ends of electrical quantities on six-phase transmission line are decoupled into six separate sequence components, of which opposite positive fault sequence component is independent with load current in typical six-phase transmission system, the scheme utilizes the sum of forementioned fault sequence components and same positive current sequence component and opposite negative current sequence component in proportion as the operating current in phase comparison pilot protection. The theoretical analysis and result of simulation confirm that the new scheme can correctly reflect any fault of the six-phase transmission lines, and it can overcome the disadvantages of the conventional protection under conditions of power swing, heavy load current and high transition resistances, and it can improve the sensitivity of phase comparison pilot protection and be used on six-phase transmission lines as main protection.