Uhv Transmission Lines, Over-voltage And Simulation

Along with the development of electric power industry, it is necessary to develop the UHV transmission system in our country. At present, the UHV transmission has been the future backbone of electric power grid in China, and its security and reliability play a critical role in the whole power system. Therefore, the relay protection, automatic control system should have excellent performance and high reliability. The over-voltage margin borne by UHV equipment is smaller than the EHV, and the loss caused by over-voltage faults on UHV equipment is greater than the EHV's, too. The over-voltage of UHV transmission lines and its restrictions have been the critical technology for the development of UHV transmission. In this paper, the over-voltage factor is researched and simulated for UHV transmission lines as well as the different restrictions to limit the over-voltage. Moreover, the impact of various methods of the over-voltage restrictions is researched, too.At first, a theoretical analysis for the mechanism of power frequency over-voltage and switching over-voltage is presented in this paper. A series of simulation and research for a UHV transmission in practice is conducted with the electromagnetic transient analysis software package PSCAD/EMTDC. As the power frequency over-voltage, the distributing voltage along the line with different mode of shunt reactor connection has been analyzed under different operation modes, including the conditions single or double sources connected with long line and fault to ground. The influence on the UHV transmission system with SVC is demonstrated as well as its ability to improve the voltage quality. On the other hand, simulation of the opening or closure processes which caused the switching over-voltage is also studied in this paper, and some exact data and operation rules for such over-voltage are obtained. The characteristic of breakers with a parallel resistor is simulated as well as the restrictions role to the switching over-voltage of MOA.After the theory and simulation research, the common rules of over-voltage at UHV transmission line is obtained, the methods of restrictions on the over-voltage is proposed as well as the protection measures, the effective control strategy is designed, and some relevant conclusions is given in the end of the paper.