The substation grounding system is an essential part of the overall electrical system. The proper
grounding of a substation is important for the following two reasons:
1. It provides a means of dissipating electric current into the earth without exceeding the operating
limits of the equipment.
2. It provides a safe environment to protect personnel in the vicinity of grounded facilities from the
dangers of electric shock under fault conditions.
The grounding system includes all of the interconnected grounding facilities in the substation area,
including the ground grid, overhead ground wires, neutral conductors, underground cables, foundations,
deep well, etc. The ground grid consists of horizontal interconnected bare conductors (mat) and
ground rods. The design of the ground grid to control voltage levels to safe values should consider the
total grounding system to provide a safe system at an economical cost.
The following information is mainly concerned with personnel safety. The information regarding the
grounding system resistance, grid current, and ground potential rise can also be used to determine if the
operating limits of the equipment will be exceeded.
Safe grounding requires the interaction of two grounding systems:
1. Intentional ground, consisting of grounding systems buried at some depth below the earth’s
surface
2. Accidental ground, temporarily established by a person exposed to a potential gradient in the
vicinity of a grounded facility
It is often assumed that any grounded object can be safely touched. A low substation ground resistance is
not, in itself, a guarantee of safety. There is no simple relation between the resistance of the grounding
system as a whole and the maximum shock current to which a person might be exposed.