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The Working Principle of Oil-immersed Transformers and the Role of Transformer Oil

Ⅰ. Understand the oil-immersed transformer

Oil-immersed transformer: rely on oil as cooling medium, such as oil-immersed self-cooling, oil-immersed air-cooled, oil-immersed water-cooled and forced oil circulation, etc. Generally, the main transformer of the step-up station is oil-immersed, and the transformation ratio is 20KV/500KV, or 20KV/220KV. Generally, the power plant is used to drive the transformer with its own load (such as coal mill, induced draft fan, blower fan, circulating water pump, etc.). The factory transformer is also an oil-immersed transformer, and its transformation ratio is 20KV/6KV.

Ⅱ. Working principle of oil-immersed transformer

There is an iron core in the oil-immersed transformer, and there are two mutually insulated windings wound on the iron core. Among them, the side connected to the power supply is called the primary winding, and the side that outputs electric energy is called the secondary winding. When the AC power supply voltage is applied to the primary winding, an alternating current flows through the winding, generating alternating magnetic flux in the iron core. This alternating magnetic flux not only passes through the primary winding, but also passes through the secondary winding, and the induced electric potentials E1 and E2 are generated in the two windings respectively. At this time, if the secondary side winding is connected to the load of the external circuit, a current flows into the load, that is, the secondary side winding has power output. The ratio of the induced electromotive force of the primary and secondary sides of the oil-immersed transformer is equal to the ratio of the turns of the primary and secondary side windings. Therefore, when the number of turns of the primary and secondary side windings of the transformer is different, the voltage can be changed. Compared with ordinary transformers, its cooling method is slightly different. During the operation of oil-immersed power transformers, the heat of windings and iron cores is first transferred to the oil, and then transferred to the cooling medium through the oil.

Ⅲ. The role of transformer oil in oil-immersed transformers

The role of transformer oil in oil-immersed transformers is the same as that of ordinary configuration transformers. There are three main functions.

1. Insulation. The first function of oil-immersed transformer oil is insulation, and the insulation strength of transformer oil is much higher than that of air. The insulating material is soaked in oil, which can not only improve the insulation strength, but also protect it from the erosion of moisture.

2. Heat dissipation. The second function of transformer oil is heat dissipation. The transformer oil of the oil-immersed transformer has a large specific heat and can be used as a coolant. The heat generated during the operation of the transformer can cause the oil close to the iron core and winding to expand and rise. Through the convection of the oil up and down, the heat is dissipated through the radiator to ensure the normal operation of the transformer.

3. Arc suppression. The third role of transformer oil in oil-immersed transformers is arc suppression. On oil circuit breakers and on-load tap taps for transformers, arcing occurs when the contacts switch. Transformer oil has good thermal conductivity. Under the high temperature of the arc, it will decompose a large amount of gas and generate a large pressure, which improves the arc extinguishing performance of the medium and makes the arc extinguish quickly.

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