Why Stones are used in Switchyard, What will be size of stone and thickness of stone layer used in Switchyard?

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we see that almost all Switchyards of substations are covered with stone (gravel) as shown in figure. What is the main reason for that. What will be size of stone and what is the thickness of stone layer.

switchyard

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AJAZ UL HAQ Changed status to publish September 19, 2023
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The main reason of  laying of grit (stone/gravel) in electrical switchyards serves a crucial role in enhancing safety by increasing soil resistivity. High soil resistivity mitigating step and touch potential, reducing the risk of electric shocks.

Step Potential : Step potential means the difference in voltage between your feet when you stand close to a faulty power line, and each foot touches an area with different electrical voltages.

Step Potential

 

Touch Potential : Touch potential is the voltage  you feel when you touch a live object with your feet on the ground. Sometimes, this touch voltage can be almost the same as the entire voltage in the grounded object, especially if the object is connected to the ground at a different place than where you touch it.

Touch Potential

The Size of Stone / Gravel is 3cm to 5cm and the thickness of stone / gravel layer should be minimum 10cm.

The other advantages of laying Stone / gravel in switchyard are

  1. The Stone / gravel prevents weeds, climbers and other plants from growing in the switchyard.
  2. Inside a switchyard, there are transformers that contain oil. Sometimes, this oil can spill, The spilled oil goes down into the ground through the grit or stones. It doesn’t stay on the top surface. if there’s a fire, the top area doesn’t catch fire. This stops the fire from spreading in the switchyard.
AJAZ UL HAQ Changed status to publish September 20, 2023
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