Research Of Overvoltage Characteristics Caused By Ground Fault In UHVDC Transmission System

In recent years, China is accelerating the construction of the UHVDC transmission project, gradually achieve the optimal allocation of energy resources, and effectively relieve the contradiction between economic development and energy demand. UHVDC power transmission can save a lot of resources of the transmission corridor, it will assume important functions in western China and overseas power transmission, at the same time it’s also an important part of the construction of strong and smart grid.±800kV UHVDC transmission project is the highest voltage level of HVDC project that among operating HVDC project in the world today. Therefore, it propose higher request of overvoltage and insulation coordination for UHVDC transmission project, so we need intensive research on insulation coordination, and with the most reasonable cost to limit overvoltage in a reasonable level under various working conditions. To ensure equipment is safe enough on basis of the arrester configuration as simple as possible so that can achieve a economical and safe operation goal.First, for all kinds of electromagnetic transient simulation software are carefully compared, and select PSCAD/EMTDC as a simulation tool. According to ±800kV Yun-Guang UHVDC transmission project operating parameters, with reference to the CIGRE HVDC transmission standard model control strategy, and finish the model of UHVDC transmission system structures. With smoothing reactor two schemes of separate arrangement or not, the measuring point 52,91,92 and 91 are simulated and compared in turn, and calculate PCOV of each point.Ground fault in AC side, ground fault in converter station and ground fault on DC line are simulated in this paper, voltage level of each point in converter station has been calculated when ground fault occurred, and comparison of overvoltage characteristics by ground fault in rectifier side and inverter side has been researched. Research shows that overvoltage will appear at DC line interface when single-phase ground fault occurs on AC bus in rectifier side, by and large overvoltage level in rectifier side is higher than inverter side, and overvoltage will not appear in inverter side by ground fault on AC bus. The smoothing reactor which is arranged on DC line and neutral bus will appear high level overvoltage by ground fault at the top of DC thyristor valve in converter station, and by and large overvoltage level in rectifier side is slightly higher than inverter side; both rectifier side and inverter side will appear the most serious overvoltage at measured point 52 by single-phase ground fault at valve side of converter transformer; in addition to the DC line has a higher level of overvoltage while is not to the others each point by the top of DC thyristor valve short to neutral bus. Overvoltage will appear on non-fault pole by fault of DC line short to ground, especially the non-faulty pole will appear very high level overvoltage by ground fault occurred at the middle of the line, and a very high level current would flow through the fault point.