Power system earthing – its commissioning and test errors

Abstract

This paper is a case study of an earthing system commissioning test, the associated errors and how to compensate for them. When measuring the impedance of an earth grid it is important to realise that there are many factors that can influence the test results. Inductive coupling between the current lead and remote earth lead and not being at remote soil potential are such factors that must be considered when determining the earth grid impedance. Often, errors due to inductive and conductive coupling are unavoidable because of the layout of the test circuit and the size of the earthing system or existence of MEN, transmission or distribution power lines, etc. For this reason, computer modelling is essential to correct interactions between the test circuit and earth grid under test, and interactions within the test circuit itself.