The transformer oil is deteriorated due to the influence of resin and sediment produced by environmental pollution and oxidation, or its appearance will be changed when the transformer has faults. It is the most basic and intuitionistic method to judge and analyze the transformer oil and its operating conditions by using the appearance of oil.

Good transformer oil sample

Use a glass cup to take a small amount of oil sample from the sampling valve at the bottom of the transformer, and carefully observe it against the sun. Good transformer oil should be clean and bright, free of sediment, mechanical impurities, suspended substances and cotton wadding substances, and the color should be light yellow.

The oil sample is brown or brown

Its acid value and water-soluble acid are often close to or exceed the international standard note value, but its chromatographic analysis has no certain regularity. In general, for transformer oil with darker color, chemical supervision test shall be strengthened to shorten the realization period, or it can be said that it is not suitable for reuse. The transformer oil shall be regenerated to prevent accidents.

The oil color of the oil sample is dark

In the simplified analysis, the acid value and water-soluble acid are seriously beyond the standard. Generally, if the oil color is dark, it may be the aging phenomenon of the oil, and there is no fault inside the transformer.

The oil color of the oil sample is black

In its simplified analysis, the flash point is often close to or lower than the limit value required by international standards. In chromatographic analysis, the increase of hydrogen and acetylene components is also an important feature. In general, the blackening of the oil color can be judged as the possible discharge phenomenon in the transformer, which is also a discharge and overpotential phenomenon. The transformer oil blackens due to the carbonization of the solid medium of the transformer. In case of serious discharge, the equipment will be burnt, and even an explosion accident will occur. If the lightning is too low, the transformer will be subject to fire or even explosion. Pay special attention to the oil with black color and low flash point.

The oil sample is turbid and white

In the simplified analysis, the reduction of breakdown voltage and the increase of hydrogen gas content are two important characteristics of the oil turbidity and whitening. In general, if the oil sample is turbid and white, it is likely that the oil contains water, which can be roughly diagnosed as water ingress into the transformer oil. Here is a simple method to roughly know the dielectric strength tester of distribution transformer to judge. Take a colorless, transparent and dried flat bottomed glass cup, and take a small amount of oil sample from the sampling valve at the bottom of the transformer to form a 7cm high oil column in the glass cup. At the place with sufficient light, stick the bottom of the cup tightly to the newspaper, and look through the oil column from above. If you can see the quiet sign, the breakdown voltage of the oil sample is above 25kV. During the operation of 10kV distribution transformer, the air strike voltage of insulating oil shall not be less than 25kV.

The above can be used as a preliminary judgment on the quality of transformer oil and possible faults of transformer. At the same time, the oil chemistry supervision test items that need to be carried out can be defined according to the different abnormal conditions, so as to make further accurate diagnosis of equipment failures as early as possible.