Study of Directional Relay´s Performances for Transmission Line´s Multiple Faults

In order to sustain the stability of the power system, the power line carrier direction protection, as the main protection, is required to rapidly and exactly and selectively remove the fault in the high voltage or extra-high voltage system of our county. Thus directional relay used by protection equipment must be able to correctly and rapidly reflect the orientation of the fault site, namely positive direction or negative direction. At present, the generally used directional relays based on the sequence components, transient energy directional relay and variation of power frequency component based directional relay etc. can rapidly and correctly determine the orientation of the fault site when a single fault or multiple faults with the same orientation occur in the power system and such directional relays have comparatively high sensitivity. But when faults at different directional sites simultaneously occur on the different phases within the protected range, abnormal performance of directional relays above would appear, and which would finally result in the fault being removed with time delay or the non-action of protection relays. This paper theoretically analyzes this abnormal performance of directional relays mentioned above, and RTDS (real time digital simulation) dynamic simulation test results prove this point. And an integrated directional relay with high sensitivity is presented in this paper, which could exactly and quickly act under the multiple fault conditions. Theoretical analysis and lots of dynamic simulation tests show that the integrated directional relay presented in the paper could quickly and precisely decide the fault site direction under multiple fault conditions, with the same sensitivity as that under the single fault condition