Transformer oil quality requirements mainly include:
1. It should have good electrical insulation performance, high insulation strength and low dielectric loss.
2. Low viscosity, fast heat dissipation and good cooling performance, which can transfer heat generated by transformer in operation.
3. It has good antioxidant stability and long service life.
4. Low freezing point and good low temperature activity.
5. High flash point and low evaporation to ensure safe operation at operating temperature (up to about 90 C).
Because the transformer runs for a long time, it is unavoidable to replenish oil. At the same time, the equipment stops changing oil after stopping maintenance.
Therefore, the oil replenishment and replacement of transformer oil should comply with GB/T14542-2000 Guidelines for Maintenance and Management of Transformer Oil in Operation. The main points are as follows:
1. Transformer oils that are in conformity with relevant new oil specifications and have not been used should be preferentially selected when oil filling of electrical equipment is short of supplementary oil. It is better to add the same oil base, the same brand and the same type of additive. The characteristics of refueling products should be no less than that of the oil in the equipment. When the amount of new oil is small, such as less than 5%, there is usually no problem. However, if the amount of new oil is large, the sludge precipitation test should be done before the oil is filled. It is confirmed that there is no sludge precipitation. Only when the acid value and medium loss factor are not greater than the oil in the equipment, can the oil be stopped.
2. It is not suitable to mix different oil base oil standards.
Under special conditions, if new oils of different grades are to be mixed, the actual solidification point of the mixture should be determined to suit the requirements of the region, and then the mixed oil experiment should be stopped, and the results of the mixed samples should not be worse than that of the worst single oil sample.
If new or used oils of different grades are mixed in the running oils, besides determining the freezing point of the mixture beforehand, the aging and sludge tests should be stopped, and the sludge precipitation condition should be observed. No precipitation can be used. The results of the mixed samples obtained should be no worse than those of the original running oils, and the ability to decide on the mixing application should be adopted.
With regard to imported oil or oil of unknown origin from consumers, it should not be mixed with different grades of running oil on the criterion. When it is necessary to mix, the aging test of mixed oil and mixed oil should be stopped beforehand. In the absence of sludge precipitation, the quality of mixed oil should not be lower than that of original running oil before mixing; if all the mixed oils are new oils, they can be mixed. The quality should be no less than the worst kind of oil, and the demand should be determined according to the measured condensation point whether it can be suitable for use in the region.
When stopping the mixing experiment, the mixing ratio of the oil sample should be the same as that used in practice; if the mixing ratio is uncertain, the 1:1 mass ratio should be used to stop the experiment.
3. Notes for oil change: fundamentally the same as the request for oil replenishment, but transformer oil should be cleaned as far as possible, so as not to reduce the quality of new oil.