A Computing Method Based Graph Theory for Shunt Coefficient of Overhead Ground Wire Under Grounding Fault Occurred Within Substation

Shunt coefficient of overhead ground wire is a fundamental data to determine the target value of grounding resistance within substation.A method based graph theory to calculated the shunt coefficient of overhead ground wire under single-phase ground fault occurred within substation with multi power sources is proposed.By means of analyzing the factors impacting the shunt of overhead ground wire when short-circuit fault occurs within substation,a circuit model is given and on the basis of graph theory,Thevenin's theorem,Norton's equivalence principle and nodal method of analysis a formula of calculating shunt coefficient of overhead ground wire is derived.Taking a quoted calculation example for instance,comparison of the data calculated by the proposed method with its original calculation results shows that the proposed calculation method based on equivalent circuit model is correct.Calculation results of an actual example show that the shunt coefficient of overhead ground wire increases with the increase of grounding resistance value within faulty substation and decreases with the increase of grounding resistance value of transmission tower;the system consisting of the first 15 towers and overhead ground wire plays decisive role to shunt coefficient of overhead ground wire.