This paper firstly evaluated the impedance method and traveling waves method for fault location, and studied the robustness of fault location method based on im-pedance. Then it proposed an assembled fault location method for a transmission line based on single-terminal electrical quantities, in which the fault zone was firstly determined by impedance method with robustness then the accurate fault position was pinpointed by traveling waves method. EMTP (Electromagnetic Transient Pro-gram) simulations showed that the proposed method can overcome the drawbacks of impedance method and traveling waves method when either one is used alone, and improve both the accuracy and the reliability of fault location.
For quickly clearing up a fault of distribution lines, which concerned with complex structure and operating modes, a directional comparison protection is necessary. The paper evaluated the traditional directional relay through modeling a typical distribution system and presented a novel negative sequence directional relay and a new directional comparison protection scheme specially designed for distribution systems. In the relay and the protection scheme, a particular negative sequence component has been constructed to solve the problem that there is no negative sequence component in a symmetrical fault case so that they could operate correctly in both asymmetrical fault and symmetrical fault. Extensive EMTP simulation studies proved that the protection schemes are able to provide fast and reliable responses for all fault conditions. In particular, they are able to give correct responses adapting to the change of system operation conditions, including the changing of system configuration, power flow direction, and source and tapped-offload conditions.
