With every new technological breakthrough, the engineering sector evolves and advances. The human body and how it reacts when placed in peril, such as electrocution, was intensely studied by Charles Dalziel. Dalziel's study shall be looked at in detail in this blog, and further, we shall learn about the terms potential rise, step potential and touch potential.
A Penetrating Investigation with a Human Body:
Yeah! Recently I read about Charles Dalziel's experiment on the human body and on animals to study the response of electrocution, which was quite a heart-stopping article. He could push the boundaries of what was known till then as the data obtained proved that the different people could survive other threshold stress voltages, i. e. the results were probabilistic. The concept he could explain through the experiment was the rise of earth potential due to the electric fault occurrence, which caused step and touch potential. It is essential for people who work with electric current and high voltage devices to be aware of the rise of potential and its effects.
The Phenomenon of Ground Potential Rise:
Typically, at electric substations, power plants and high power transmission lines rise of potential is commonly experienced as they are exposed to extreme environments and placed in open areas. This potential ground rise is potential gradients or potential differences on the earth's surface caused by significantly high electric fault event dissipation into the ground. As the soil resistivity is never zero, the electric potential rise of high strength can be in the vicinity of their earthing grids. Subsequently, any associated electric network or conductive devices in the proximity may get energized and can be catastrophic - posing a threat to human life and causing extensive equipment damage.
The rise of ground potential needs to be computed before designing an earthing grid for power and telecom sectors coordinated with power fed from substations and transmission lines. Step, touch and transfer potential are the experienced hazards due to the rise of potential.
Computing the Potential Rise in Step and Touch Perspective:
1. Step Potential:
You may have energized objects near where the fault current bursts into the ground. If a person stands near such an energized object, then he/ she may experience electric shock due to the difference in potential between the person's feet and the object. This path paved for current transfer during normal, or fault conditions through any person's leg are called step potential. Hence, it's essential to understand that an energized object spreads the current over the ground surface before going deeper into the ground, so a person staying near the associated object can be at risk of serious injuries.
2. Touch Potential:
Conduction of high current into the ground can induce touch voltage when any person comes in contact with an energized object. The total fault current travelling through transmission towers and dissipating through earth rod can be the touch potential for the utility workers within 1 meter of the earthing system. This fault energizes objects in the vicinity further. It threatens the person touching and coming in contact with the thing; in some instances, touch voltage could be nearly equal to the total voltage.
Proper designing and placement of earthing systems provided with necessary insulations are the criteria for minimizing step and touch potential.
Learn about proactive and critical grounding strategies along with the use of CDEGS designing – visit our website www.jmv.co.in.
Related Post:
Earthing System for 50 Years of Protection
To operate the electric network in balanced conditions, protective devices with the proper earthing system are recommended in IS/ IEC 61643 and IS 3043 which suggest using a maintenance-free earthing system (involving copper bonded steel rod and earth enhancement compound).
