Analysis And Suppression Measures Of Over Voltage Of 35kV Shunt Capacitor

To reduce the power loss in the process of transmission and improve the economicalefficiency of power system, a lot of load in power system need reactive power compensation while the shunt capacitor is usually used as the reactive power compensation device. The shunt capacitor need frequent input and removal due to load variation, and operating overvoltagewhich is harmful to power system cannot be avoided generally during the cut-off of the shunt capacitor by the circuit breaker.Therefore, it is significantto carry out the research on overvoltage generating mechanism and restraining measures.The correlative research work will be presented in the next few sections.Firstly, overvoltage transient process caused by the cut-off of the shunt capacitor is analyzed in theory. Based on the capacitance voltage equation, reactor voltage equation and loop current equation, the corresponding waveforms could be acquired by MATLAB software. Ignoring several factors, the whole system can be equivalent to a simple circuit to calculate the value of overvoltage in different situations, such as normal opening, single-phase reignition, and two-phase reignition.Based on actual operating data of a substation, electromagnetic transient simulation model of 35 k Vshunt capacitor can be constructed by ATP-EMTP software. In several conditions,such asnormal opening, single-phase reignition, and two-phase reignition, the overvoltage value can be calculated by simulation analysis. The correctness of the simulation model could be verified by comparison between simulation value and theoreticalvalue.Considering the variation of reactance rate,the influence on overvoltage value will be analyzed in the third chapter. With the massive introduction of DGs in substation, the influence on overvoltage value will bealso analyzed by altering the interconnected location, capacity or numbers of DGs.Then, the basic structure and principle of metal oxide arrester(MOA) is presented. Three types of MOA are designed according to the traditional wiring mode of MOA which are used to analyze and compare the inhibitory effect towards overvoltage. Conclusion on characteristics and application conditions of each MOA can be acquired by simulation analysis.Resistance-capacitance absorbing device is the other approach to deal with overvoltage, and the value of R and C could be calculated reasonably based on the presented principle. The comparison of inhibitory effect between two main methods is stated in the end.Finally, three schemes which combine MOA with Resistance-capacitance absorbing device to restrain overvoltage are proposed. By comparing the inhibitory effect, the most reasonable scheme can be selectedaccording to the generating cause of overvoltage.