Preliminary testing and assessment of safety conditions of HV substations located in urban areas

Abstract

This paper presents a method enabling the elimination of the inductive influence of metal installations surrounding a test circuit on the estimated value of grounding system impedance in a tested HV substation. By disregarding this influence, the preliminarily estimated values of the ground potential rise and potential differences (touch and step voltages) within and in the vicinity of an HV substation can be significantly smaller in comparison to their actual values. Due to this, the definite assessment concerning the safety conditions in some HV substations can be considered as satisfied although it is not the case. The analytical part of the presented test method is developed on the basis of the analysis of a complex electrical circuit formed by many, known and unknown, inductively and conductively coupled elements during a simulated ground fault in the tested substation. The developed analytical expressions are based on the measured values of two currents obtained by simulated ground-fault in the tested substation. One of them is a simulated ground-fault current, while the other current is the one induced in one of the phase conductors included in the test circuit only for obtaining this induced current.