Phase-controlled Switching Shunt Capacitor System

Shunt Capacitor Bank is one of the important devices for reactive power compensators in power system,so its security and reliability,which draw public attentions,are significant for the whole power system.The over voltage and inrush current which occur in the process of closing or opening the capacitor are two main factors,affecting the safe operation.In early power system,these two problems were not satisfactorily solved,resulting in many accidents.The two traditional methods to the problems are applying over voltage restraint device and improving the switching device breaking capacity,but unable to get to the root of the problems.Intelligent phase controlled switching has become reliable and economical to reduce switching surges.By phase-control closing and opening,this controlled switching device can restrain or eliminate the over voltage and inrush current during the operation.This thesis studies the application of intelligent phase-controlled switching device for shunt capacitor banks,as following:By studying the generation mechanism of closing inrush current and opening over voltage,the concept and components of intelligent phase controlled system are presented here and the overall design proposal is also put forward in this thesis.By combined this system and vacuum circuit breaker with permanent magnetic actuator,the phase controlled closing and opening of shunt capacitor banks are realized.According to the real operation in power system,for capacitors in three phrase star connections with isolated neutral point system,the ’AB +C’ strategy is choosed.Based on MATLAB,the simulation program for intelligent phase control is presented.The simulation results indicates that this strategy plays a significant role in lowing the over voltage and inrush current.To phase-controlled switching device for shunt capacitor banks in 10 kV power system,the no-load and on-load experiments for whole device are conducted.The experimental results verify the validity of this intelligent phase controlled switching device for shunt capacitor banks.In no-load experiment,the phase control time deviation is limited in±0.5ms,meeting the system demand.In load test,the inrush current downs from several kilo-ampere to 3kA,and the mean voltage is less than 2 times.All these show that this intelligent phase controlled switching device is effective in restraining the over voltage and inrush current.