The Design Of Zero-Crossing Switch Device Based On Contactor

In the process of power transmission in grid, there is usually a lot of reactive power loss which severely effects efficiency of power transmission. Thus it is much necessary to realize reactive power compensation in proper places of grid. In industry occasions, low-voltage terminal is often chose to install reactive power compensation equipment that include reactive power compensation controller, switches and capacitors, among which the performance of switches determine the effect of reactive power compensation directly.The subject was derived from the cooperation project between Chongqing University and Guizhou XHK Holdings Limited. Three Problems exist in actual operation process of throwing and cutting capacitor for users such as tedious manipulation steps, optimization of switching operation control, lack of efficient monitoring of abnormal status and inaccuracy of moment determination of capacitors etc. Focusing on these problems, the works are mainly described as follows in the paper:Firstly, comparison of switches mostly used currently was done. According to their structure characteristic and control scheme, the merit and demerit was analyzed, the practical need of users was further analyzed in the process of throwing and cutting capacitors and a sort of design scheme was proposed for device of zero crossing switching capacitor using contactors.Secondly, focus on the switch operation performance and the out of place about monitoring protection, the indicator module and auxiliary control module for switching were designed, including the acquisition and real-time display of both current and voltage, model optimization of manual / automatic control, real-time mode choosing of total / divided compensation, as well as monitoring and protecting of abnormal status Besides, the corresponding systemic circuit and control program were designed.Then, based on the analysis of reason that capacitor switching time is not accurate enough, zero crossing detection circuit based on fast optical coupler was proposed. Its advantage over comparator circuit was demonstrated by simulation computing. The action moment prediction model of contactor was built and the according switching control strategy was given according to its connection mode of capacitors so that precise zero-crossing switching could be completed.Finally, corresponding experiment platform was built, experimental test on the basis of capacitor as three-phase total compensation was finished, and the actual operation conditions were observed. Switches device assure the stability and reliability of operation.