Research On The Protective Scheme Of Thyristor Controlled Transformer-type Controlled Shunt Reactor

Controllable shunt reactor(CSR)is one of the key elements used in power system for reactive power compensation.The stable operation of power system depends on the safe and reliable operation of CSR,and this correspondingly raised high protection requirements for CSR.The protection for a thyristor controlled transformer-type controlled shunt reactor(TCTCSR),which has rarely been studied,is more complex than that of other CSRs because it comprises not only working winding but also the control winding and compensation winding.This paper focus on the protective scheme of TCTCSR and the research includes three parts:configuration and fundamental principle of TCTCSR,electromagnetic transient modeling,protection configuration,and turn-to-turn fault protection for the control winding.Firstly,this paper introduces the configuration and operating feature of the conventional TCTCSR.According to the analysis of control characteristic and harmonic content,it is concluded that the 6-pulse control winding in Y-connection,valve branch in Y-connection form have the advantages of relatively flat control curve,maximum adjustment range and best harmonic characteristics.Consequently,this connection form is selected as the foundation for further study.Based on the configuration,the digital simulation model of TCTCSR is built in MATLAB/SIMULINK.Simulations of all possible faults within TCTCSR are carried out on the basis of the built model.Combined with fault simulation,the overall protective scheme for the TCTCSR is designed,among which the hep point is the analysis and study of the fault characteristics for all possibel faults of contrl winding.It could be concluded from the analysis that for control winding to ground fault and valve short circuit fault,differential protection sensitively is not accurate enough when the CT is installed in the original position of control winding.On the other hand,in case of certain small inter turn fault,the protection sensitivity of diffrential protection and zero sequence power protection that based on the net side winding electrical characteristics needs to be improved,while the self-generated zero-sequence current from fundamental wave has significant variation.Therefore,the new interturn protection scheme for contril winding that based on the fundamental zero-sequence overcurrent protection with blocked zero-sequence voltage is proposed.Finally,the outlook for the further study of TCTCSR is presented.It is stressed that during the protection scheme study,not only the protection itself needs to be taken into consideration,but the coordination of protection and control also needs to be empasized.Besides,the protection that concerning controlling and system level,which is not studied in this paper,still need to be further studied.