Research On Wide-Area Back-Up Protection System With Substation As Basic Unit

Relay protection, as the first line of defence of the power system, not only need to clear the fault fastly, accurately and reliable, but also to assure the system keeps stable when the fault is cleared. But the power network is complicated; the tradition protection exposes many problems which are ascribed to the information only from the local measurement, lack of the global observation for the whole system. Well, the development of the computer and the communication technology provide the oppurtunity to the theory of the Wide-area protection.Firstly, a few basic principles of the transmission line back-up protection and the influence factors are presented in this thesis. And then, the development background and the research status are simplely introduced. The wide-area back-up protection system with substation as basic unit is presented in this thesis.This back-up system cooporates with the traditional main protection and the back-up protection and takes the responsibility to protect the whole power network.According to the wide use of the PMUs in the wide-area system, a fault location algorithm which is based on the fault current component is presented in this thesis. This algorithm uses the value of the fault current component measured from two side of the line is added as the actuating quantity; meanwhile, the value of fault voltage component measured from two side of the line to get the value of the virtual current as the restraining quantity. Then the ratio of the two current components constitutes the protection criterion. The principle of this algorithm is simple, can identify the fault transmission line correctly. And the simulation verifies that this algorithm has good sensitivity and reliability.Because the algorithm of the wide-area protection based on the synchronized phasor measurement ask for a high synchronization of the information. Once the information measured from two side of the line is desynchronizing, the accuracy of the algorithm will be influenced seriously. Another back-up protection scheme based on the union back-up protection information for a transmission network which has a main substation is described in this thesis. This scheme only uses the information of operation signals of the relays in the protected area to identify the fault line. The principle of this scheme is also simple, and it simplifies the setting rules and requires little information. The results show that this scheme is exact against N-1operation statuses that can improve the performance of the back-up protection system.