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Why Put Pebbles Under the Transformer?

Mar. 15, 2024

We can often see a large number of pebbles placed under some transformers, so what are these pebbles used for? Just for aesthetics?


Our common transformers are divided into dry-type transformers and oil-immersed transformers:

Oil-immersed transformers use oil as the main insulation method of the transformer and rely on oil as the cooling medium, such as oil-immersed self-cooling, oil-immersed air-cooling, oil-immersed water cooling and forced oil circulation. The main components of the transformer include core, winding, oil tank, oil pillow, breather, explosion-proof pipe (pressure release valve), radiator, insulating bushing, tap changer, gas relay, thermometer, oil purifier, etc.

Compared with dry-type transformers, oil-immersed transformers have the characteristics of low cost, easy maintenance, and can solve the problem of large-capacity heat dissipation and high-voltage insulation problems of the transformer. However, because the cooling oil of oil-immersed transformers is flammable, it leads to oil-immersed transformers. Transformers have inherent disadvantages, that is, they are flammable and explosive.


At this time, a series of components such as pebbles came into being; this part under the transformer is usually called the oil unloading pool or oil unloading pit (or similar names), leading to the accident oil pit or accident oil pool.

When an accident occurs, such as oil injection or explosion, the oil from the transformer will be discharged into the oil unloading pit and then flow to the accident oil pool.

Some pools have grilles, and some do not. If the grille is used, the pebbles are placed on the grille; if the grille is not made, the pebbles are placed in the oil unloading pit. Whether to use a barrier or not depends on the transformer type, capacity, and voltage level. There are regulations in this regard.

When placing pebbles under the oil-immersed transformer, the following seven factors are mainly considered:


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1. After the transformer is used for a long time, the parts may have problems such as aging and leakage. Placing a large number of pebbles can absorb the oil leakage of the transformer and allow the transformer oil to flow back to the accident oil pool smoothly, reducing the occurrence of accidents;

2. In the event of an accident, cobblestones can prevent oil in the transformer from splashing and explosion.

3. When there is an explosion and fire, cobblestones can play an isolation role to prevent the fire from spreading to the ground, which is helpful for extinguishing the fire.

4. Slight cooling effect. When the temperature of the transformer is too high, you can use pebbles to cool it.

5. Pebbles are insulated to facilitate maintenance and inspection by operating personnel.

6. Pebbles have a shock-absorbing effect. The function is the same as the stones on the railway, which can add a layer of buffering.

7. Prevent weeds from growing.


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