Study On New Principle Of Wide-area Protection To Deal With High Resistance Ground Fault

Single-phase grounding fault is the most frequent fault on power line,and its probability is as high as 90%.From the recorded data.A considerable part of phase-to-phase fault is developed from single-phase grounding fault.Therefore,improving the fault removal ability of the transmission system for single-phase grounding fault can greatly enhance the reliability of the system.Due to the uneven distribution of energy in China,the transmission lines are far away from each other,and the special landform distribution in China makes the setting up environment of the transmission lines changeable,especially the mountainous landform,which is prone to high resistance grounding fault,and the existing main protection is difficult to deal with.When the primary protection fails to respond to high resistance failure,the last barrier to high resistance failure will be zero sequence IV protection.However,there is at least an action delay of more than 1.5s from the start to the action of zero-sequence IV protection,and the fault removal time is very long,which will bring the risk of fault conversion and fault development.Therefore,on the premise of supplementing the existing protection,it is of great significance to study the protection that can realize high resistance fault resection before the delay action of zero sequence IV protection after the main protection misoperation.This paper analysis the radiant network under the zero sequence voltage and current distribution characteristic of modulus,pointed out that in zero sequence radiant network single-phase high resistance earth fault occurs,the busbar voltage modulus maximum near the short-circuit point,modulus maximum fault line of zero sequence current,and zero sequence current modulus to busbar is diminishing ladder from short-circuit point to two side step by step.It is pointed out that the zero-sequence current modulus and zero-sequence voltage modulus can be used to construct the criteria for the removal of high-resistance faults.The local loop network topology is analyzed,and the zero-sequence current modulus distribution is found to be different from that of radial network.Next,based on the distribution characteristics of zero sequence current modulus,a new protection principle that can realize the asynchronous information dependence of high resistance fault is proposed,and the applicability of the protection principle under different topologies is deeply analyzed.Simulation results show that the proposed protection criterion can effectively remove high-resistance faults without relying on synchronization.On this basis,in order to solve the problem of poor sensitivity of protection criteria under local loop network topology,a new protection principle with high sensitivity based on zero-sequence voltage and current modulus ordering in the presence of local loop network topology was proposed.The simulation on PSCAD/EMTDC verified its effectiveness for high-resistance faults.In order to improve the operating efficiency of protection in case of information loss,based on the zero sequence capacitance current naturally existing in transmission lines in case of out-of-area faults,a differential protection based on zero sequence current modulus is designed.The correlation simulation shows that the differential protection criterion based on the zero sequence current modulus only needs to correlate the zero sequence current and voltage modulus of the line to complete the fault status judgment of a single line.