Substation grounding systems provide protection from electric shock hazards by dissipating electric currents into the earth during fault conditions. Safe grounding requires both an intentional grounding system buried below the earth's surface and an accidental ground temporarily established through contact between a person and the substation. Electric shock accidents can occur when high fault currents meet conditions that allow current to pass through a person, such as through soil with high potential gradients or direct contact between the body and two points of different potential. The risks of electric shock increase with current magnitude and duration, so high-speed fault clearing is important to reduce exposure time and injury risks.

1. Substation Grounding
by
Mangesh S Kulkarni
Sharad Institute of Technology College of Engineering , Yadrav-Ichalkranji

2. Reasons for Substation Grounding System
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.

3. 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

4. The circumstances that make human
Electric shock accidents
• Relatively high fault current to ground in relation to the area of
the grounding system and its resistance to remote earth.
• Soil resistivity and distribution of ground currents such that
high potential gradients may occur at points at the earth
surface.
• Presence of a person at such a point, time, and position that the
body is bridging two points of high potential difference.
• Absence of sufficient contact resistance or other series
resistance to limit current through the body to a safe value
under the above circumstances.
• Duration of the fault and body contact and, hence, of the flow of
current through a human body for a sufficient time to cause
harm at the given current intensity.

5. Accidental Ground Circuit

9. Permissible Body Current Limits
• duration, magnitude, and frequency of the current affect the
human body
• most dangerous impact- Ventricular Fibrillation
• Perception, Muscular contraction, Unconsciousness,
fibrillation, respiratory nerve blockage, and burning

10. • slight tingling sensation- 1mA
• Sensation- between 1 and 6 mA
• loss of muscular control- 9–25 mA
• Slightly higher currents, breathing may become very
difficult, caused by the muscular contractions of the chest
muscles.
• ventricular fibrillation- 60–100 mA
• Larger currents will inflict nerve damage and burning,
causing other life-threatening Conditions.

11. Importance of High-Speed Fault Clearing
• Probability of exposure to electric shock is greatly reduced by
fast fault clearing time
• chance of severe injury or death is greatly reduced if the
duration of a current flow through the body is very brief