Grounding at power substations is extremely important. The grounding system provides the ground connection for the grounded neutral for transformers, reactors, and capacitors and also the discharge path for lightning rods, arresters, gaps, and similar devices. It ensures safety to operating personnel by limiting potential differences, which can exist in a substation.
Substation grounding provides a means of discharging and de-energizing equipment in order to proceed with maintenance on the equipment.
It also provides a sufficiently low-resistance path to the ground to minimize the rise in ground potential with respect to remote ground.
Substation safety requirements call for the grounding of all exposed metal parts of switches, structures, transformer tanks, metal walkways, fences, steelwork of buildings, switchboards, instrument transformer secondaries, etc. This means that a person touching or near any of this equipment cannot receive a dangerous shock if a high-tension conductor flashes to or comes in contact with any of the equipment listed.
This means that each individual piece of equipment, each structural column, etc., must have its own connection to the station grounding mat.
A most useful source of information concerning substation grounding is contained in the comprehensive guide IEEE Standard 80, IEEE Guide for Safety in AC Substation Grounding.