The Research On Adaptive Strategy Of The Arc-Suppression Coil Based On Thyristor Control

With the demand of urban distribution network transformation,many urban overhead lines are gradually changed into underground power cable lines.The single-phase grounding fault capacitive current of arc-suppression coil grounding system is increasing continuously.If the tuning is improper,arc grounding overvoltage and phase to phase short circuit are easy to occur.Most of the existing arc suppression devices can not accurately compensate the fault capacitive current,but the arc suppression effect is not ideal.In order to realize the full compensation of capacitive fault current,it is necessary to study the full compensation arc-suppression coil with fast response,high accuracy,simple and reliable control and high cost performance ratio.This dissertation presents a new adaptive strategy based on bidirectional thyristor control.Firstly,this dissertation studies the operation principle of arc-suppression coil through neutral point grounding,constructs voltage resonance model in normal operation and current resonance model in single-phase grounding fault,deduces the basic relationship between relevant parameters,summarizes several existing arc-suppression coils in distribution network,analyzes its structure and compensation control strategy,and points out the shortcomings of existing tuning technology.Secondly,based on the widely used arc-suppression coil with adjustable turn,this dissertation improves a main auxiliary full compensation arc suppression device.The structure of the device includes three parts: main arc suppression device,auxiliary arc suppression device and bidirectional thyristor.The main and auxiliary arc suppression device adopts the ‘pre-regulation type' tuning compensation mode which combines the pre-regulation and the random adjustment type.It does not need series or parallel voltage limiting resistors to limit the neutral point displacement voltage,which simplifies the arc suppression device.Then,on the basis of analyzing the control strategy of the controllable series compensation,the method of correcting command impedance by error feedback is improved and applied to the control system of arc-suppression coil for the first time.In normal operation,the main arc-suppression coil is set at over compensation,the auxiliary arc-suppression coil adopts the PI impedance control principle of trigger angle correction,and the bidirectional thyristor adopts the control strategy of trigger angle correction,so that the arc-suppression coil can realize adaptive control.In case of single-phase grounding fault,under the premise of introducing small harmonic component,the capacitive current can be suppressed to the greatest extent and the grounding fault can be fully compensated the effect of capacitive reactive power component of barrier current.Finally,in PSCAD / EMTDC environment,the simulation models of medium and small 10 k V distribution network are built respectively.The cable is used as the transmission line,and the various states of the neutral point through resonant grounding system(including neutral point ungrounded,resonant grounding and fully compensated resonant grounding)are simulated,and the influence of single-phase fault point is analyzed and compared,and the most common single-phase grounding fault occurs in the simulation distribution network when the fault occurs,the compensation effect of the arc-suppression coil to ground capacitive current verifies the correctness and effectiveness of the proposed adaptive control strategy.