Step Voltage (Es) is defined as the maximum potential difference that exists between the feet when a fault current flows in the body.
Touch Voltage (Et) can be defined as the maximum potential difference that exists between an earthed metallic structure capable to be touched by the hand and any point of the ground, when a fault current flows.
Step and touch potential occurs due to the short circuit current flows on the conductor.
All the substation is provided with the good grounding system or low resistance path to the fault current.
Therefore to provide the high resistance for foot and ground, the stones are provided.
Stones eliminate the growth of small weeds and plants inside the switchyard or transformer yard
It protects the moisture content evaporation and keeps the ground wet.
Most in switchyard Power Transformers insulated with the insulation oil.
The insulating oil spillages catches fire easily.
So Stones/Gravel is provided to protect from fire when oil spillage takes place.
Moisture on the floor level get minimized.
Compensate the vibration in the transformer which has been caused due to magnetostriction in core
Improves yard working condition.
It restricts entering of snakes and other reptiles as the surface would be inconvenient to crawl.
There is a BIG NO to the grass as they and other weeds and tiny plants grow which makes troubles in case of rain and humidity. In addition, the dry grass may catch fire and there are chances of short circuits during the operation.
Using stones in the switchyard provides protection against the entry of wildlife animals and snakes, lizards, rats etc in the substation area.
Gravel yard prevents the formation of puddles and accumulation of water in the switchyard which is not a good sign in case of high voltage equipment.
Pebbles and stones are more shock resistant as compared to grass and sand therefore, it will reduce the vibration in the transformer (caused by Magnetostriction in core) and special cases like earthquakes etc.
Stone and gravels increase the resistance of soil which leads to reduce the limit of touch and step potential. This way, it reduces the risk of electric shock hazard during general maintenance and operational works.
Stone in the switchyard improves the overall working conditions and smooth operation of an electric substation and protection against electric shock in existing of proper grounding systems.
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