Safety design planning of ground grid for outdoor substations in MEA's power distribution system

This paper analyzes the performance of grounding system that is made of copper conductors and significantly influenced by soil resistivity. The grounding performance is evaluated in terms of ground potential rise, touch voltage and step voltage caused by a short circuit that generates a flow of large currents in the aboveground structures and grounding system and dissipates in the soil. These currents may cause damage to substation equipment and may be dangerous to personnel working nearby. Safety design planning for step and touch voltage for the existing fault level and future fault levels are presented for utility applications where personnel hazards may exist. Modeling and simulation is carried out on the Current Distribution Electromagnetic interference Grounding and Soil structure (CDEGS) program. The safety design planning is illustrated by a practical case of ground grid design for the 69/12– 24 kV, indoor-type Pathumwan substation of Metropolitan Electricity Authority (MEA).