Due to the long operating time of transformers, oil replenishment is inevitable, and oil changes after major equipment repairs are also common. Therefore, the principle of replacing transformer oil should be as follows:

1. It is best to use the same brand of oil as the original equipment for refueling;

2. Require both parties to add the same antioxidant or neither party to contain it;

3. The mixed parties have good quality and performance indicators that meet the standards of working oil or new oil;

4. If one of the working oil indicators approaches the limit value of the control standard, a mixing test should be conducted; If one or more indicators are not qualified, the oil should be purified or regenerated before mixing;

5. New oil of the same brand can be mixed in any proportion as long as the indicators are qualified; Mixing new oil of the same brand with running oil that has already started to age or is close to the operating oil index. use;

6. If different grades of new oil are mixed with unaged working oil, a freezing point test should be conducted to determine their usability; If mixed with oil that has already aged and is close to the working oil index, in addition to the freezing point test, a sludge sedimentation test should also be conducted. Only after all are qualified can they be used;

7. When importing or mixing oil from unknown sources with operating oil, aging tests should be conducted on each oil sample and mixed oil in advance. Only after the mixed oil quality is qualified can it be mixed. Not lower than the quality of the operating oil; If the mixed oil is brand new, after aging testing, the quality of the mixed oil is not lower than the worst oil.

The principles of oil change and oil replenishment are basically the same, but transformer oil should be drained as much as possible to prevent the quality of new oil from deteriorating.