The paper presents an original analytical procedure which enables a quick and, for practical purposes sufficiently accurate evaluation of the significant parts of the ground fault current, for a fault at any of the towers of a transmission line of an arbitrary number of spans. The advantages of the method are the simplicity and accuracy of the formulae for solving uniform ladder circuits of any size (from one up to an infinite number of pis) and 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 presented method is suitable for analyses aimed at evaluating the maximum substation grounding system fault current, at selecting the ground wire capable of withstanding the fault currents and at the prediction of step and touch voltages near transmission towers.

Practical method for evaluating ground fault current distribution in station, towers and ground wire

An advanced methodology and a computer model for analysis of practical grounding systems based on the method of moments are presented. The practical methodology is applicable to both simple and complex grounding systems. The grounding system may consist of cylindrical conductors as well as rectangular earth conductors or metallic surfaces buried in earth or located on the surface of the earth. The method consists of computing an equivalent circuit model of the earth embedded electrodes and conductive soil. Uniform or two-layer soil can he accommodated. The problem of computational efficiency is addressed. Several innovations have been introduced to minimize execution time, including adaptive segmentation of grounding structures and adaptive computation of self and mutual impedances. The procedure enables accurate computation of touch and step voltages, body currents, grounding system impedance, voltage profile, etc. The method and computer program have been validated with actual system measurements. >

An advanced computer model for grounding system analysis

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.

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

When a ground fault occurs at a substation, the part of the fault current that flows between the grounding system and the surrounding earth is known as grid current. This current determines the magnitude of the dangerous voltages within and around the station. It may vary from a few percent to almost 100% of the earth fault current. It is necessary to make an accurate estimate of grid current for an economical and safe design of ground electrode. The available analytical methods for determining the grid current require complete system data, which is voluminous and often unavailable. In this paper a simple and accurate analytical method for determining the grid current is presented. The method requires limited data. A computer program based on the proposed method has been developed and tested.

A practical approach for computation of grid current

When a substation is fed by a combined overhead-cable transmission line, a significant part of the ground fault current flows through cable sheaths and is discharged into the soil at the transition station where cables are connected to the overhead line. Such a phenomenon, known as ldquofault application transfer,rdquo may result in high ground potentials at the transition station which may cause shocks and equipment damage. The scope of this paper is to present new analytic formulas which can be used for the direct calculation of the fault current transferred at the transition station and its ground potential rise as well as the substation earth current. The proposed formulas allow evaluating the influence of the main factors to the fault application transfer phenomenon and can be employed, at the preliminary design stage, to easily assess the most appropriate safety conditions to avoid dangerous effects.

A Simple Method for Evaluating Ground-Fault Current Transfer at the Transition Station of a Combined Overhead-Cable Line

This paper presents recent developmental advances for the computation of maximum ground potential rise of grounding structures or alternatively maximum earth current in substation grounding systems. An advanced methodology for short circuit analysis is presented. The methodology is based on modeling of power system elements in direct phase quantities. Coupled with equivalency techniques, it provides an extremely efficient algorithm for performing numerous sequential short circuit analyses. An easy to use computer program has been developed under EPRI sponsorship. The computer algorithm uses the methodology to search for the fault condition which yields the maximum earth current in a substation grounding system. The methodology has been validated with actual system measurement on a Georgia Power Company Substation. Validation results are presented. Typical results as well as program utilization factors are discussed. The results demonstrate that the worst fault location is highly dependent on system parameters and cannot be predicted with simple rules.

Computation Of Maximum Earth Current In Substation Switchyards

The determination of the maximum current to be used to design a safe grounding system has been receiving a lot of attention in recent years. For years, most engineers used 'the total substation bus ground fault current to design the grounding system. A few engineers may have taken into account the fact that some of the ground fault current simply circulates through the grid conductor between its source and the fault point. Today, the determination of the maximum grid current is being scrutinized more closely. Computer analysis is being used to determine a more accurate value for the maximum grid current, resulting in the design of more cost-effective, yet safe, grounding systems./l/ Another reason for the need to more accurately determine the grid current is that the everincreasing fault current magnitudes are also increasing the grid potential rise (GPR), making it difficult and expensive to protect communication circuits. Many recent papers have described methods for computing the actual fault current flowing between the grounding system and surrounding earth./4-7, 12, 14, 17-19/ These methods generally account for the effects of the source(s) of fault current, as well as other ground fault current return paths (i.e., overhead ground wires, feeder neutrals, etc).

S. G. Patel

Papers

Computation Of Maximum Earth Current In Substation Switchyards

Determination of Maximum Substation Grounding System Fault Current Using Graphical Analysis