| Valve hall grounding switches is bulky and its structure is complex. Installing overmany grounding switches in valve hall not only influences the electric field distribution and the best security air distance, but also occupys large space volume and increases the floor area of valve hall. Project construction and operation experience shows that many of valve hall grounding switches and other related equipment are imported, which are expensive. Installing overmany grounding switches have significant influence on environmental protection and economic efficiency of valve hall construction. Therefore, it is important to choose suitable grounding switch configuration in the process of valve hall optimization design. Grounding switch configuration optimization must considers safety problem, for reasons that grounding switches is directly related to the safety of system operation. Converter valve consists of a large number of inductances and capacitances. Some electric charges will be remained when the valve is blocked, which not only threatens the security of maintenance personnel but also delays the maintenance time resulting in suffocated recovery of electrical power supply. Therefore, study on valve energy relief mechanization is also important which is related to grounding switch configuration optimization.This paper presents the idea of using zero-input response of linear network to investigate the mechanism of residual energy release in blocked valve hall. Based on the analysis of valve hall modular decomposition, utilizing electric network theory solves zero-input response of valve arm and makes an preliminary analysis of the source of residual energy and its influence factor. Then build an ±1100kV HVDC transmission system model with detailed thyristor valve module in PSCAD/EMTDC to get the source and the release road of residual energy in converter valve and to analysis the influence of different valve group blocking ways and grounding switch configurations on residual energy discharge process. At last, this paper presents an economic and applicative configuration of valve hall grounding switch.This paper investigate residual energy release mechanization in converter valve and valve hall grounding switch configuration in detail with theoretical analysis and simulation calculation. The results show that the voltage of key point presents an dampening trend which is decided by hyperbolic function. The voltage amplitude is greatly influenced by the residual electric charge in the junction capacitance of thyristor at the blocking time, which decreases when the specific value of thyristor junction capacitance and valve arm stray capacitance increases. The constant voltage decay time τ is mainly decided by the parameter of damped circuit and voltage-sharing resistance of thyristor in converter valves. The residual magnetic energy in valve hall can be negligible while the electric field energy stores in the thyristor capacitance can not be ignored. The release progress of electric field energy is influenced by thyristor damped capacitance and resistance. The grounding switch configuration has a significant influence on the valve hall energy decay time. Grounding switches should be installed on the valve sides of the two transformers connected to 12-pulse converter, where the residual energy decay time is around 16.7s which is shorter than that of no grounding switch by about 81%. When using two grounding switches installing on the valve side of the Y/Y and Y/D converter transformers connected to single 12-pulse converter valve, namely configuration of Y1D1, the energy decay time is only longer than that with six grounding switches by 0.14 s. Considering the economic efficiency,applicability and security of the actual economic, grounding switch configuration of Y1D1 is recommended. |
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