Study On Neutral Grounding Modes Of35KV Cable Network In Wind Farm

Due to the influence of the terrain and environment, more and more cables arechosen as the35kV electric transmission line in the wind farm. With the scale of thewind farm expanding, the length of the cable increasing, then the system capacitivecurrent is higher. If system occurs single-phase grounding fault, it would be a seriousthreat to the insulation of electrical equipment. Because of the relationship between theneutral grounding modes of the electric power system and the single-phase ground faultis most closely, so choosing a reasonable neutral grounding mode can improve thereliability and economy of35kV power grid, thus it is a great significance to the safetyof wind farm.The paper takes Long-li wind farm as the research object, creates the simulationmodel of35kV cable network of wind farm by using Matlab/Simulink software;Considering the time and capacitive current of grounding fault, the location andtransition resistance of fault, the paper analyzes the over-voltage level and over-currentlevel of the cable network on different neutral grounding modes, which includes neutralungrounding, neutral via petersen coil, and neutral via low resistance. Then through acomprehensive comparison, researches a revised neutral grounding mode, which issuited to the35kV cable network of wind farm. The paper gets the followingconclusions:①By taking different grounding modes for different grounding faults. Neutral viapetersen coil can effectively compensate grounding capacitive current, which have apositive effect on fast arc extinguishing; Neutral via low resistance can inhibit transientovervoltage, which can fast remove fault by zero-sequence overcurrent protection.②The improved neutral grounding mode which combines the advantages of fastarc extinguishing of neutral via petersen coil and fast remove fault of neutral via lowresistance. By calculating the transient process of the improved neutral grounding mode,the process of transient switching does not cause shocks to the system, and does notaffect the safety operation of the equipments.Based on the characteristics of the wind farm35kV cable network, the paper getsan improved neutral grounding mode, which suit to the35kV cable network of windfarm. Namely based on the neutral via petersen coil, if the cable network occurssingle-phase grounding fault and the grounding capacitive current is less than100A, the short time switching of medium resistance can limit transient overvoltage level in theinitial period of the fault; if the cable network occurs transient grounding fault, thegrounding arc can extinguish by the compensate coils. Otherwise put a low resistance toincrease the ground current, then the zero sequence over current protection device willstart to remove the fault. For the grounding capacitive current is greater than100A,without using transient overvoltage suppression measures, the cable network occursnon-transient grounding fault, the zero sequence over current protection device will startby putting a low resistance.