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Denis Baptista
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Asked: 2020-02-23T21:12:48+00:00 In:

What is the reason behind using stones/gravel in electrical substations (switchyards)?

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What is the reason behind using stones/gravel in electrical substations (switchyards)?

A substation is a part of an electrical generation, transmission and distribution system. The main principle of a substation is to transform high voltage to low voltage or execute various other important functions. Electric power may run through various substations at different voltage levels between the generating station and the consumer. In substations, the transformers may adjust the voltage rates between high and lower transmission voltages or when two separate transmission voltages are related.

Why we use stones instead of sand or soil in switchyards?

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    1. Yago Florez
      Level 2

      The reason behind using stones/gravel in electrical substations for resistance purposes. We need to increase resistance when a person is on the switchboard/sub-station area to prevent electric shocks during failure.
      The resistance of stones is higher as compared to the resistance of sand and grass. The resistance of stones is up to 10,000 or maybe 9,000 ohmmeters. It makes it more feasible due to its cost and availability.

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    3. Paula Balderas
      Level 1

      In Electrical substations (switchyards) stones are used rather than sand or grass for the following reasons : 

      • Stones are used in the substation to reduce the risk of steps and touch potential when operators work on a switchyard as step and touch potential increase during a short circuit. We can define step potential as the potential between the two feet of a man on ground or an animal if a short circuit occurs. This results in current flow in the body resulting in an electrical shock. Touch potential is created by a combination of ground and equipment when a person touches the body during a failure. In short circuit situations, as operator touch the electrical equipment, failure flows through the human body.
      • Power transformers mounted at substations have oil as a cooling and insulating medium. Oil leakage happens during service, or when changing the oil of transformers. The oil spillage capable of catching fire is risky for switchyard activity. Stones are, therefore, one of the solutions given to protect the oil from burning. 
      • Stones eliminate the growth of small weeds and plants inside the switchyard.
      • The use of stone can also increase the towering footing resistance and improve the yards working conditions.
      • It also absorbs moisture in plain grounds when the grass grows and cause damage to the transmission lines, and it will also form current leakage. Therefore, it prevents the growth of small weeds and plants in the switchyard.  
      • It avoids water pools during rainy seasons as water flows under the stones.
      • It protects against wildlife and other species such as snake, which find it difficult to crawl in such areas.
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