Research On The Simulation Modeling And Protective Scheme Of New-type Magnetically Controlled Shunt Reactor

Controllable shunt reactor(CSR)is one of the key elements used in power system for reactive power compensation.The system reactive power balance and voltage stability depends on the safe and reliable operation of CSR.Protection for the CSR,therefore,needs to pay much attention to.The protection for a magnetically controlled shunt reactor(MCSR),which has rarely been studied,is more complex than that for other CSRs because MCSR comprises not only working winding but also the control winding and compensation winding.This paper focus on the protective scheme of MCSR and the research includes five parts,they are configuration and fundamental principle of MCSR,electromagnetic transient modeling,protection configuration,turn-to-turn fault protection for the control winding and transients of different energization modes.Firstly,this papaer introduces the configuration and operating feature of the conventional MCSR and the new-tpye MCSR.Distortion of the flux in main cores caused by changing the working winding configuration of a conventional MCSR from parallel-connection to series-connection is investigated.A new physical design for the control windings of a MCSR that can solve the problem of flux distortion is presented and the principle of which is analyzed.Based on the configuration of new-type MCSR,the five-section magnetic circuit model is deduced according to Kirchhoff's magnetic circuit theorem and Ampere circuital theorem.The numerical simulation model of the MCSR is built in PSCAD/EMTDC and MATLAB/SIMULINK.Simulations of all possible faults in the MCSR are carried out.Combined with fault simulation,the overall protective scheme for the MCSR is designed.Considering the control winding protection is the most difficult part in MCSR protection,the fault feature and problems to the control winding protection are analyzed.It is shown that conventional zero-sequence and negative-sequence directional overcurrent protections are not sufficiently sensitive against turn-to-turn faults occured in the control winding.Besides,the overvoltage protection on dc buses is not suitble either becuase the ac overvoltage on dc buses during a turn-to-turn fault tends to be intermittent voltage spikes rather than standard sinusoidal waveform and the fault feature may even not exist in some cases.Cause of the problem is investigated and it is proved that the appearance of overvoltage on dc buses is dependent on zero-crossing of the total control current.A new protective scheme that is capable of detecting control widing turn-to-turn fault with enough sensitivity by using fundamental component in the total control current is proposed.Finally,the transient process of pre-excited energization and direct energization of MCSR,the effects of the two energization modes,including overvoltage and inrush current,are compared.It is proved that pre-excited energization is capable of suppressing the overvoltage and alleviating the harmonic problem,which is superior to direct energization.Therefore pre-excited energization is recommended for the application of MCSR.