Research On The New Principle And Adaptability Of Protection Against Turn-to-turn Faults In Magnetically Controlled Shunt Reactors

As an critical reactive power compensation device in a high-voltage power grid,the safety and stability of magnetically controlled shunt reactor(MCSR)is essential for the reactive balance and voltage stability of the system.However,the structure of MCSR is complex,and the possibility of turn-to-turn fault is high.Besides,under the combined influence of AC and DC excitation,the tun-to-turn fault features become complex than traditional fixed shunt reactors.Therefore,the difficulty of protection scheme design against turn-to-turn faults in MCSR increases.Focusing on the protection against the turn-to-turn faults in MCSR,the following are studied in this paper:the present protection configuration against turn-to-turn faults and its performance analysis;characteristics,impact on the protection against turn-to-turn faults and countermeasures of the energization process of MCSR;characteristics,impact on the protection against turn-to-turn faults and countermeasures during the large-scale capacity adjustment of MCSR;and novel protection principles against turn-to-turn faults in MCSR based on equivalent leakage inductance parameters.Firstly,on the basis of the working principle and model construction of MCSR,the current protection configuration against turn-to-turn faults in MCSR and the performance are studied.It is concluded that the protection still has the following problems requiring to be solved:①The reliability and sensitivity of the protection against turn-to-turn faults are insufficient;②The adaptability of the protection under complex operating conditions is not clear.Secondly,aiming at a complex operation condition of MCSR—the transient process of energization,its characteristics,impact on the protection against turn-to-turn faults and the countermeasures are studied.The transient characteristics of the main electrical quantities during energization are studied.It is concluded that the protection against the turn-to-turn faults based on the fundamental component of the total control current may be affected during the energization process.To solve this problem,countermeasure based on the ratio of the fundamental component in control winding currents to that in the total control current,and the countermeasure based on the autocorrelation of the control winding current waveform are proposed.The anti-maloperation strategy effectively solves the problem of the protection against turn-to-turn faults to misoperate during the MCSR energization process.Thirdly,aiming at another complicated operation condition of MCSR—large-scale capacity adjustment,its transient characteristics,impact on the protection against turn-to-turn faults and the countermeasures are studied.The transient characteristics of the main electrical quantities during arge-scale capacity adjustment are studied.It is concluded that the protection against the turn-to-turn faults based on the fundamental component of the total control current has the risk of misoperation during the capacity adjustment process.According to the characteristic that the fundamental components of the three-phase control winding currents are approximately equal during the capacity adjustment process,the difference among the fundamental components of the three-phase control winding currents are used to build the identification criterion of the capacity adjustment process.The proposed strategy effectively solves the problem of protection maloperation.Lastly,a new protection principle against the turn-to-turn faults in MCSR based on equivalent leakage inductance parameters is proposed.Based on the calculation model of the equivalent leakage inductance parameters,the recursive least square method is used to identify the equivalent leakage inductance parameters.The protection is built by using the change of equivalent leakage inductance parameters before and after the fault and the difference of the parameters among three phases.Simulation and physical experiments show that the proposed new protection principle against turn-to-turn faults solves the problems of low sensitivity and cannot identify faulty windings.The proposed protection has important value for actual engineering.