Quantitative analysis of voltage distribution within ±1100kv HVDC converter valve tower under various triasient over-voltage conditions

As is widely recognized, lightning has always been a threatening factor for power system. Consequently, the protection against lightning must be taken into consideration when new technologies are introduced to the power system. Besides, with the ability to transmit high voltage, large capacity power stably over a long distance, High Voltage Direct Current (HVDC) systems have become an important part of the strong smart grid of China. As the core equipment of HVDC converter station, the thyristor valve will be exposed to different kinds of overvoltage originating in the AC and DC systems. The safety and reliability of the power systems depends on the capacity to withstand overvoltage of thyristor valve on a great extent. In this paper, choosing ±1100 kV DC converter valve tower as the research object, under the overvoltage insulation testing conditions, a simulation model is established, a new kind of analysis algorithm is put forward and authenticated, the over-voltage analysis is accomplished. Based on the detailed physical structure of converter valve, broadband circuit modeling of ±1100 kV thyristor modules and capacitance parameter, an overvoltage analysis model of ±1100 kV DC converter valve tower is established. After that, a new method of converter valve tower overvoltage analysis has been put forward, which could avoid the deficiencies of the existing research methods effectively. On the basis of the previous work, the non-uniform coefficient concept is introduced to analyze overvoltage in valve tower. Through numerous calculations, the voltage distribution characteristics of the key device in the converter valve are gained when the converter valve is exposed to lightning overvoltage and fast front overvoltage. Besides, the quantitative analysis of influencing factors of the voltage distribution non-uniform coefficient is also presented in the paper.