Practical method for evaluating ground fault current distribution in station supplied by an unhomogeneous line

The paper presents an analytical procedure which enables a quick and, at the design stage, correct evaluation of the ground fault current distribution, for a fault in a substation supplied by a line composed of two or more uniform and different sections. The advantages of the method are based on the simplicity and accuracy of the formulae for solving uniform lumped parameter ladder circuits of any size and under any terminal conditions. The formulae are obtained by applying the "general equations of the line represented by discrete parameters" on a specific electrical circuit formed by a transmission line ground wire during ground faults. The paper also derives simple and exact expressions for solving ladder circuits formed by the discretization of underground conductors which are in continuous contact with earth (e.g.: the sheaths of a cable, an interconnecting copper buried in the soil, a pipeline, etc.). The correct prediction of the expected ground fault current parts in soil and neutral conductors is of great importance in designing safe and economical substation grounding installations.