Testing and evaluating grounding systems for substations located in urban areas

This study presents a method that enables elimination of the influence of metal installations surrounding a test circuit on the results of measurements. For substations located in urban areas, this influence is unavoidable and so intensive that it cannot be disregarded. Consequently, the test values of the potential differences (touch and step voltages) appearing on the grounding system and grounding system impedance can be significantly different in comparison with the actual values. Owing to this, estimated safety conditions of certain urban high-voltage/medium-voltage substations may be completely incorrect. The presented analytical method is developed on the basis of analysis of a complex electrical circuit formed during the ground fault by feeding line conductors and the many different metal installations involved with a fluctuating magnetic field around and along the feeding line.