Why Do Oil-immersed Transformers Need to Be Refueled Regularly?

Oil-immersed transformers are soaked in oil. It is inseparable from transformer oil. Transformer oil is a liquid component. It is different from gasoline and diesel used in machines. Transformer oil is normal in various transformers. It plays an irreplaceable role in the operation. Oil-immersed transformers need to be regularly added with transformer oil, otherwise they will not work normally. Why should oil-immersed transformers be refueled regularly?

Ⅰ. Reasons for regular refueling of oil-immersed transformers

1. The oil-immersed transformer is equipped with a respirator. Although there is a desiccant inside the respirator, long-term operation will inevitably increase the moisture content of the transformer oil. The result of the increase of moisture is the reduction of the insulating ability; 2. The oil-immersed transformer may generate discharge between coil turns and bare conductors during operation, and the discharge can carbonize the transformer oil. However, each discharge may not cause an accident, but the cumulative insulation capacity of the transformer oil will be reduced; 3. The oil-immersed transformer oil inevitably contacts with the air and will oxidize for a long time. It will also reduce the insulating capacity of the transformer oil.

Ⅱ. How to ensure the normal operation of oil-immersed transformers?

1. Ensure the temperature and temperature rise within the specified range. When the ambient temperature is 40°C, the limit working temperature of the distribution oil-immersed transformer winding is 105°C, and the upper oil temperature of the oil-immersed transformer does not exceed 85°C. If the oil temperature exceeds the allowable value, it is easy to cause the insulation deterioration and damage of the oil-immersed transformer. In addition, more windings can rise to 65°C, and the oil temperature in the upper part can rise to 45°C for a long time. As long as the temperature of the upper oil does not exceed the specified value, the oil-immersed transformer can operate safely within the specified service life.

2. Pay attention to overload. In the event of an accident, in order to ensure the continuous power supply of the main electrical equipment, the fault can be quickly eliminated, and the distribution oil-immersed transformer can be overloaded in a short time. However, at this time, forced air cooling measures should be taken to control the upper oil temperature within 95°C. Otherwise, the insulating oil will deteriorate, which will eventually damage the oil-immersed transformer.

3. Maintain the balance of three-phase load. Special attention should be paid to the symmetry of the three-phase load on the secondary side. When the three-phase load is too large to cause imbalance, the voltage of one-phase load will drop, and the voltage of one light load will become higher, and the deviation will expand to a certain extent, threatening the safety of electrical equipment.

4. Ensure that the allowable variation of the power supply voltage does not exceed the rated value. If the voltage of the oil-immersed transformer increases, the secondary voltage of the oil-immersed transformer will also increase, and if the secondary voltage of the oil-immersed transformer increases, it will be harmful. Therefore, the supply voltage of oil-immersed transformers usually does not exceed 5% of the rated value.