Simulation And Study On Switching Overvoltage At DC Side Of ±800kV UHVDC Converter Station

Studying the overvoltage of DC power transmission system is one of the key parts to the UHVDC Project. The insulation levels of the converter station equipments directly affect the overall cost of the project. In this paper, the switching overvoltage of UHVDC converter station were simulated and discussed.Firstly, the generation mechanism of switching overvoltage at DC side of the converter station is introduced. Combined with previous research results, the typical operating conditions which used to calculate the switching overvoltage were listed. Then, based on the ±800kV UHVDC project, the DC transmission system transient calculation model which includes monopolar ground loop circuit and unipolar metal loop circuit were established by using the PSCAD/EMTDC electromagnetic transient software.Based on the last breaker’s trip and the AC system short-circuit fault, the AC bus overvoltage is simulated and analyzed. In addition, in the calculation process, the impact of these factors such as the short-circuit capacity of AC power system, the operating voltage of AC bus, the transmission power on the calculation results were analyzed. Strictly taken into account when calculating converter valve overvoltage, the double faults which contains the single-phase ground fault of the converter transformer valve side and the ground fault of the DC line were discussed, and the maximum overvoltage of the valve arrester were listed. When studying the overvoltage of DC polar line, select three typical fault conditions which contain the full-voltage startup of the DC transmission system, the last breaker’s trip and the inverter blocking without by-pass de-blocking to simulate and calculate. According to the calculating results, we can identify the decisive calculation fault.For the neutral bus overvoltage, the two operation modes of monopolar ground circuit loop and unipolar metal circuit loop were considered. For each operation mode, both DC system ground fault and neutral line disconnection fault were simulated and the effects of different fault points on the calculation results were analyzed. Finally, the transient rating of DC filters of Hami-Zhengzhou UHVDC project were calculated, and the calculation results can provide a reference for selection and insulation coordinationg of the components.