Research On Adaptive Overcurrent Protection Technology For Wind Farm Transmission Lines

During the 14 th Five Year Plan period,the wind power industry has shifted from a high-speed development stage to a high-quality development stage centered on technology development.Renewable energy represented by wind power remains the focus of the national energy strategy,and the safe and stable operation of wind farms is of great significance to the power system.The tripping accident of the collection line is the most representative accident that wind farms have caused to the power system,and the setting of the protection setting of the collection line is an important reason for the tripping accident of the collection line in wind farms.The article studies the adaptive overcurrent protection technology for power transmission lines,improves and optimizes existing power transmission line protection schemes,improves the protection performance of power transmission lines,and provides new ideas for solving power transmission line tripping accidents in wind farms.The article analyzes the factors that affect the short-circuit current of the wind farms collection line protection configuration an d setting scheme,and the impact of the reactive compensation current provided by the low voltage ride through process of the doubly fed wind turbine on the reliability of the collection line protection setting value.Taking a certain wind farm as an example,the calculation method of the collection line protection setting value is provided.In addition,the impact of changes in system operation mode on the reliability of line protection was studied.Secondly,in order to solve the problems existing in the current protection of power transmission lines,adaptive technology is used to propose an adaptive protection method suitable for wind farm power transmission lines.The overcurrent section Ⅰ protection is changed to an inverse time current protection with a voltage correction coefficient,and the action time limit is set online by detecting the faulty current and the bus voltage after the fault,This solution effectively solves the problem that the overcurrent protection of the current collection line Ⅰ cannot distinguish internal faults of the high-voltage side fuse of the box transformer,and improves the current situation of excessive sensitivity and poor selectivity of overcurrent protection in section Ⅰ;The installation of directional discrimination elements in the overcurrent section Ⅱ effectively solves the problem of protection malfunction caused by low voltage through current of the doubly fed fan.Improve the existing zero sequence section Ⅱ protection scheme by collecting the zero sequence current flowing through the grounding resistor during faults.When the zero sequence protection of the grounding transformer is activated,adaptively adjust the zero sequence section Ⅱ protection setting of the collection line online.This scheme can reduce the risk of grounding faults and misoperation of the grounding transformer protection on two or more collection lines at the same time,and effectively prevent the expansion of accident scope.After using the adaptive zero sequence protection scheme,it effectively prevents the further expansion of the fault range and reduces the risk of misoperation of the zero sequence protection of the grounding transformer when a transition resistance grounding fault occurs simultaneously in the collection line.protection.Finally,an equivalent model of a doubly fed wind farm was built using simulation software PSCAD,and the optimality and correctness of adaptive protection for wind farm transmission lines were verified through experiments.The simulation experiment results show that adaptive overcurrent protection can distinguish faults between the high-voltage side fuse of the box transformer to the fan and the end of the line to the busbar.When a three-phase short circuit fault occurs in the line,the protection can quickly remove the fault,prioritize ensuring the speed of relay protection,and reduce the impact on the power grid and other faulty lines.When a two-phase short circuit fault occurs at the end of the line,speed should be sacrificed to ensure its selectivity,and overcurrent protection correctly distinguishes the fault area through action time delay;When the zero sequence protection of the grounding transformer in the wind farm is triggered,the adaptive zero sequence section Ⅱ protection is enabled for the collection line.Based on the collected zero sequence current value,the protection setting is recalculated to reduce the risk of misoperation of the grounding transformer zero sequence protection.