Study On The Zero Sequence Protection Of Wind Farm And Its Single-phase Ground Fault Location

With the increasing penetration of wind power in the power system,the fault of the wind farm will seriously affect the safe operation of the power system.In response to the problem that large-scale wind turbine off the network recently,《Eighteen Major Anti Accident Measures of the State Grid Corporation))proposing to change the wind farm main transformer from ungrounded to resistance grounded and provide ground protection to solve this problem.However,the phenomenon of zero sequence protection misoperation of the small resistance grounding wind farm occurs several times in the wind farm,which seriously endangering the safe and stable operation of the power system.At the same time,there is a large error for the single-phase metallic ground fault and arc high-resistance grounding fault localization algorithm in wind farm field,which cannot achieve accurate fault location.In view of the above problems,the following work has been done.Firstly,the basic structure of the low-resistance grounded wind farm was analyzed and a simulation model was built.The single-phase earth fault characteristics of the wind farm were simulated and analyzed,and the reasons for the zero-sequence protection rejection or misoperation in the case of high-resistance grounding were theoretically analyzed.Based on simulation analysis,a self-adaptive zero-sequence protection scheme suitable for small resistance grounding wind farms is proposed.This scheme not only guarantees quick-moving protection at low-resistance grounding,but also ensures reliability at high-resistance grounding faults.Secondly,in view of the fault location of single-phase grounding fault in the field of wind farm,this paper theoretically analyzes and simulates the problems faced by the traditional range finding algorithm applied to the intra-field fault location of wind farms.The error mainly comes from the complex tree structure of the wind farm.And then this paper analyses the zero sequence network of the wind farm,an equivalent fitting method of wind turbine branch current based on zero sequence network is proposed.This method only uses the voltage and current observed at the collector line exit to fit the branch current of the wind turbines,and then proposes a fault location algorithm based on the fault section search method to improve accuracy of the traditional algorithm.The segment search method effectively reduces the error of the traditional distance measurement algorithm.The simulation results show that the algorithm is effective under different transition resistances simulation,different fault distances simulation and different types wind turbines simulation.Finally,aiming at the arc high-resistance grounding fault that easily occurs in the wind farm field,the simulation model of arc high resistance grounding fault and the fault characteristics of high resistance grounding fault in the field of wind farm are analyzed and evaluated in this paper.The applicability of the existing methods in high impedance grounding faults in the field of wind field is simulated and analyzed.The main sources of the error are analyzed in detail.A compound ranging method is proposed on the basis of the logarithmic method and the fault section search method.The compound ranging method combines the advantages of the logarithm method to effectively simulate the dynamic characteristics of the arc and the section search method to eliminate the influence of wind turbines branch.Finally,the effectiveness of the algorithm is evaluated by different arc types,different fault distances and different wind turbine types simulations.In a word,this paper proposes a self-adaptive zero-sequence protection method to improves the zero sequence algorithm of the wind farm.On the basis of the traditional fault location algorithm and the special structure of the wind farm,the paper proposes intra-field fault location algorithm and segment search method,which applicable to the wind farm intra-field fault location.