| The massive consumption of fossil energy such as coal and oil has led to severe energy crisis and environmental contamination problems,and the use of clean energy is the general trend.Compared to other clean energy sources,wind power is more efficient and clean.In recent years,wind power generation has received extensive attention from countries around the world.However,wind power generation has the characteristics of volatility,intermittency and unpredictability.When it gradually replaces traditional synchronous units and is integrated into the distribution network on a large scale,it will lead to the incompatibility of the original relay protection scheme and the neutral point grounding scheme,and reduce the safety and reliability of the power system.With regard to this,this paper conducts in-depth research on the distribution network relay protection scheme and neutral point grounding scheme for the scenario of wind power access to the distribution network,the details are as follows.First,on the basis of establishing the mathematical model of wind turbine grid connection,the double closed-loop control strategy of wind power grid connection is grasped.Then,by analyzing the power grid fault characteristics of the distribution network under symmetrical faults and asymmetrical faults,the control strategy mechanism of the wind power grid-connected system under normal operation and faults is deduced.And build a research model in PSCAD/EMTDC to verify and analyze the wind power grid-connected operation and fault characteristics.Then,aiming at the existing relay protection scheme,combined with the operation characteristics of wind power grid-connected,The influence of wind power access on single terminal protection and dual terminal protection of distribution network is analyzed.By analyzing current protection and distance protection,and an improved distance protection scheme based on wind power feed current and transition resistance compensation is proposed.Under the premise of considering the fault control strategy,using the composite sequence network of different fault types and the characteristics of wind power feed,an improved measurement impedance expression is derived to ensure the distance protection performance after wind power is connected to the grid,and at the same time improve the protection withstand transition resistance ability.This paper analyzes the influence of wind power T-type access on the original longitudinal protection of the distribution network.By adding positive sequence voltage amplitude,positive sequence voltage and positive sequence current phase angle criteria,and improve the setting value of the differential current of the pilot protection according to the characteristics of wind power output fault current limiting,and a pilot protection scheme suitable for wind power T-type access distribution network is formed.Under the fault control strategy used in this paper,the effectiveness of the improved protection scheme is verified by simulation.Finally,for the single-phase grounding fault handling in the wind power distribution network,combined with the characteristics of large capacitor current in the high-proportion cable distribution network,and taking into account the influence of the access of wind turbines on the selection of neutral point grounding in the distribution network,this paper only uses the traditional wind power access to the high-proportion cable distribution network.The single-phase grounding fault occurred in the grounding mode of the arc suppression coil was evaluated,and the optimal grounding scheme of the neutral point of the distribution network through the arc suppression coil and the small resistance in parallel,and the variable grounding method of the fan was proposed,and the fault control strategy adopted in this paper were proposed.Reducing the impact of ground fault on the stable operation of wind power and distribution network,and the simulation verification is carried out under the fault control strategy adopted in this paper. |
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