The substation earthing system comprises a grid of horizontal buried conductors connected to earthing spikes driven into the ground. This earthing mat provides several functions: ensuring personnel safety from electric shocks, providing a grounding path and discharge for over-voltages and faults. The earthing resistance is determined by how well the mat's conductors are connected and the soil resistivity - lower resistivity leads to lower resistance. Non-current carrying equipment and structures are connected to the earthing mat to limit fault voltages and currents for safety.

1. Substation Earthing System
Earthing Mat

2. The S/S earthing system comprises of:
• A grid (earth mat)
Horizontal buried conductors

3. Functions of grounding system in the S/S
• Ensure safety of personnel due to electric shocks.
• Provide grounding path (Neutral grounding).
• Discharge over-voltages (ground path for surge arrestors).
• Provide path for faults (Phase-Ground).
• Provide earth connections to the non-current carrying objects in the
s/s.

4. Earthing Mat
• Buried below ground level
• Connected conductors
• If the soil have low resistivity>> the
earthing resistance will be low as well.
• If the soil have high resistivity>> Then we
need to insert more conductors in the
mesh and connect them closer (To create
lower resistance)

5. Earthing spikes (Electrodes)
• Driven into the ground: connected to the
earthing mat
Connect it to the; equipment
bodies, structures, neutrals, etc

7. The fence, equipment
body, tanks, support,
structures, towers,
structural steelworks,
water pipes, etc. should
be earthed.

8. Earth Resistance Value
• Value of Earthing Resistance Determine the rise of the fault voltage!
• As well, limit the fault current
V = IR

11. Criteria of design S/S earthing system
• Low step voltage
• Low touch voltage
• Low earth resistance

12. Touch Voltage (E-Touch)

13. Step Voltage (E-Step)

14. Substation Grounding