Research on a Novel Traveling-Wave Protection Using Mathematical Morphology for Transmission Line Unsymmetrical Grounded Faults

Abstract

There are two primary troubles having effect on reliability in tradition traveling-wave distance protection schemes. One is reflection wave identification for single-ended traveling-wave protection (A-type), and another is time synchronization for two-ended traveling-wave protection (D- type). This paper proposes a novel protection for transmission line unsymmetrical grounded faults, which only needs initial traveling wave. The protection principle is based on the propagation time difference between aerial- and zero-mode traveling waves. The propagation time difference rises monotonously with the fault distance increasing. The protection scheme is designed both single- and two-ended type. The protection algorithm is implemented with Mathematical Morphology Gradient (MMG), which detects the traveling-wave arriving time. The performance of the traveling-wave protection scheme is investigated with a number of PSCAD/EMTDC simulation data under various fault situations. Theoretical analysis and testing results demonstrate the proposed novel protection scheme is feasible, and has a certain potential in fault location. Traveling wave protection can locate the fault using D- type two-ended scheme, which is conjunction with synchronized clock sources. When a fault occurs, a traveling wave with high frequency is generated at the fault point and then propagates along the transmission line to both directions. By time stamping the arrival of the traveling wave at each end of the line, and measuring the time difference of arrivals of the traveling wave, the fault can be located (5) . This paper proposes another protection scheme based on modulus velocity difference of traveling waves. There exists a velocity difference between aerial- and earth-mode components; Aerial mode can travel along the line at constant velocity and with little attenuation, while the earth mode velocity is decrease and with severe attenuation. This property can be used for the protection scheme. Because this scheme use fault information of single end, so it is not affected by the factor such as time synchronization and the length of the transmission lines. Mathematical morphology is a recently developed tool for signal procession which can determine the arrival time accurately when the traveling wave enters the protection relay. Numerous PSCAD simulations test the effective of the proposed protection scheme.