Case study on impact of seasonal variations of soil resistivities on substation grounding systems safety in tropical country

It is important to evaluate the validity and safety of the substation earthing system since over time the physical and electrical properties or requirements of the substation earthing can change in many ways. A research study focused on safety assessment of substation earthing systems due to variations of soil resistivities values which dependent on tropical rainfall variations was carried out on a 132kV substation. Actual earthing resistances and soil resistivities values were measured at a regular interval for a period of 18-months as input to the simulation process. The study used CDEGS™ software for modeling and assessment of substations earthing system safety. From the initial desktop simulation calculation based on the above models, it was found that the substation have its touch and step voltages exceeded the allowable limits as per IEEE 80-2000 Standard (IEEE Guide for Safety in AC Substation Grounding) for some period throughout the duration of the study.