Research Of Hybrid Middle High Voltage Switch For Reactive Power Compensation

With the rapid development of power system in our country, industrial users of the power quality requirements are getting higher and higher. The distance between power network capacity and power transmission is gradually increased, because the stable operation of the power grid is directly related to the quality of the power transmission. The reactive power in power system has been the focus of people's attention. Reactive power compensation of the power system can increase the power factor, stabilize the power grid voltage, improve the utilization rate of equipment, and improve the operation safety of the system. Only to increase the power factor as an example, whether it is for power supply enterprises or large factories, each hour will be able to improve the economic benefits of tens or even hundreds of yuan. So the reactive power compensation is of great significance to the stable operation of the power grid and the improvement of the power quality.At present, switching shunt capacitor banks is widely used for reactive power compensation in power system and a lot of problems has been made. The most important one is the transient process of overvoltage and inrush current generated by the switching capacitor banks. Therefor, a variety of devices used for reactive power compensation which is mainly to suppress the transient process as the core of the study are produced.In this paper,according to the need of reactive power compensation of power system. A novel medium voltage switch with diode and high speed switch(HSS) in parallel connection is presented. It is to solve the problem of inrush current and over voltage when interruption and making capacitor bank used in reactive power compensation of power system.The hybrid switch is composed of two parts, mechanical switch and electronic switch. The mechanical switch as the main structure consists of three high speed vacuum switch which are connected in series and respectively in the two sides of the switch that parallel two reverse diode. Through the coordination of the two parts to complete the capacitor banks switching.This paper introduce the basic structure of hybrid-switch and its principle. Analyzed the hole process of current commutation in the hybrid-switch and the diode during the interruption and making in detail and how to use the diode's feature of natural zero crossing point to allow the HSS cooperate. A simulation circuit model of the switched capacitor is established by simulink toolbox in Matlab. Compare with traditional vacuum switch, the simulation test results show that the hybrid middle-high voltage switch reduce the inrush current and over voltage.This paper also discuss the control strategy for different connections of three phase neutral point ungrounded capacitor banks. A simulation circuit model is established to verification and analysis. The result show that the hybrid switch can effectively reduce inrush current and over voltage during the interruption and making capacitor bank.Finally, based on the previous analysis and policy results, the experimental prototype of the hybrid switch for reactive power compensation is developed and the prototype is used to test the switching capacitor. The results show that the hybrid switch can effectively suppress the transient process for switching capacitor banks.