Research On Single-phase Fault Location For UHV Transmission Line

As a basic industry,power industry is closely related to the development and improvement of national economy and people’s living standard.In order to solve the contradiction between irrational allocation of resources and the demand for electricity,the grid company decided to build "three vertical and three horizontal" UHV backbone network to achieve the pattern of large-scale "West to East" and "North to South".As a hub of the power system,UHV transmission lines undertakes the important task of long-distance power transmission,and also affects the security and stability of the power grid directly.Once fault will force a large number of load shedding,even system crashes and serious accident of large scale blackout,therefore UHV transmission line fault location has been the main focus of domestic and foreign researchers.This article describes the development process and technical features of UHV power grid,and summarizes the research status of UHV transmission line protection and fault location.Based on the conclusion of the development history,mathematical models and function of series capacitor compensation and shunt reactors compensation,UHV transmission line model is established and simulated in PSCAD/EMTDC.The changes of voltage and current caused by shunt reactors and series capacitor are analyzed,and the impacts of them to the transmission line fault are summed up.As overvoltage protection of series capacitor,Metal Oxide Varistor(MOV)has non-linear volt ampere characteristic,once conducted will cause the line current is difficult to determine,fault location failed.Therefore the transient data before MOV action are dealt with the fast Fourier transform,then the power frequency are extracted,and use them as the raw data of fault location.On the basis of strong tracking filter theory and transmission line theory,this article proposes the fault location method of distributed parameter model.The fault distance and system states are considered as extended system states to joint estimation,then the fault distance can be calculated accurately.From a large number of experiments and simulations in PSCAD/EMTDC,the fault location algorithm with high precision is free from the influence of random factors such as transition resistance and fault inception time.