Safety Assessment of AC Grounding Systems Based on Voltage-Dependent Body Resistance

This paper presents the safety assessment of a grounding system at an indoor-type 161/23.9-kV substation based on voltage-dependent body resistance. For a grounding system to be safe, the maximum actual touch and step voltages should not exceed postulated safety criteria. Thus, the safety assessment of a grounding system is referred to a procedure by which the actual maximum touch and step voltages are computed and compared to the maximum allowable (safe) touch and step voltages. The safety criteria in terms of allowable body current have been defined by two widely accepted standards, i.e., the IEEE Std. 80 and the IEC 60479-1. Then, the allowable body current is translated into the allowable touch and step voltages. However, the two standards differ in their definitions of body resistance. The IEC 6047-1 provides data for the body resistance as a function of body voltage and data for the body resistance as a function of path, while the IEEE Std. 80 uses a constant value of 1000 Omega for the body resistance. Thus, a comparison of allowable touch and step voltages computed by these two standards is included in this study.