Research On Relay Protection For UHV Transmission Lines

Along with the development of China’s economy, the characteristics of the reverse distribution of energy resources and energy consumption put forward new requirements for inter regional transmission capacity of power grid. Ultra long distance and ultra large scale transmission advantages of UHV transmission provide a new way for the development of China’s power network. UHV transmission technology has broad application prospects in China. UHV AC transmission line can achieve synchronous operation of the grid. And make it be an indispensable part of China’s special high-voltage Engineering. The particularity of the UHV transmission project has brought many problems to the relay protection. As an important part of UHV power transmission project, relay protection of transmission line also has many problems. Studies on these issues will have important significance to the development of the power network.Due to the importance of UHV transmission line, it must be equipped with two sets of main protection which principles for different and fully independent. Generally speaking, these two sets of protection are always split-phase-current differential protection, and negative-sequence-directional differential protection or zero-sequence-directional differential protection. And because of the distributed capacitance of UHV transmission line, the capacitor current cannot be ignored. The reliability of the split-phase-current-differential protection has been greatly affected. This article proposed a new current differential protection based on the Bergeron model by using the fault-related component. It can avoid the influence of capacitance current very well, and improving the reliability and sensitivity of the differential protection of the phase current differential protection. The negative-sequence-directional element has the problem of refusing action when symmetric fault happened, and make it possible that the protection not work. In this paper, the author use the method of data delay and data weighting to solve this problem. It can avoid the protection tripping, and improve the reliability of relay protection. The problem of zero sequence directional element is more serious. Because of its principle, it can only react to ground fault, but helpless for the phase-to-phase fault. To solve this problem, in this paper, the author propose the method of data delay and logic-cooperation to improve the components. So that it can be able to operate correctly under all types of faults. In this paper, the PSCAD/EMTDC model of the 1000kV UHV transmission line is established by using the existing literature data, and verified the correctness of the improved method by the PSCAD/EMTDC model.