Transformer oil will deteriorate due to the influence of resin and sediment produced by environmental pollution and oxidation, or change its appearance when transformer is faulty. Applying the appearance of oil to discriminate and analyze the operation of transformer oil and transformer is the most fundamental and intuitive discriminant method.
After taking a few transformer oil samples from the sampling valve at the bottom of the transformer with a glass, and looking carefully at the sunshine, a good transformer oil should be clean and transparent, without precipitation, mechanical impurities, suspended substances and cotton flocculent substances.
First, if the color of oil sample is brown or brown, its acid value and water-soluble acid are often close to or beyond the international standards, but there is no certain regularity in chromatographic analysis. Generally speaking, for transformer oils with darker colors, chemical monitoring experiments should be strengthened to shorten the experimental period, or, in other words, it is not suitable for reuse. Transformer oil should be stopped for regeneration and disposal in order to avoid accidents.
2. If the oil color is dark, the acid value and water-soluble acid in the simplified analysis are seriously exceeded the standard. Under normal conditions, the dark oil may be the aging phenomenon of oil, and there is no fault inside the transformer.
3. If the oil sample is oily and black, the flash point in the simplified analysis 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. Under normal conditions, oil blackening can be distinguished as discharge phenomenon or discharge and overheating phenomenon in transformer. Transformer oil blackens due to carbonization of solid medium of transformer. When discharge is serious, equipment will be burned down and explosion accident will occur. Low flash point will also cause transformer fire and even explosion. Special attention should be paid to oils with dark color and low flash point.
4. If the oil sample is turbid and white, the reduction of breakdown voltage and the increase of hydrogen content are two important characteristics of the simplified analysis. Under normal conditions, if the oil sample is turbid and white, it is likely to be formed by water in the oil, which can be roughly diagnosed as moisture in the transformer oil. Here's a simple way to know about the breakdown voltage of distribution transformer oil, without using the dielectric strength tester to judge. Take a colorless transparent dried flat bottom glass and take a small amount of oil sample from the sampling valve at the bottom of the transformer to form a 7 cm high oil column in the glass. In sufficient light, press the bottom of the glass to the newspaper, and look down through the oil column from the top. If you can see No. 6 clearly, the breakdown voltage of the oil sample should be above 25 kV. In the operation of 10 kV distribution transformer, the breakdown voltage of insulation oil is not less than 25 kV.
The above can be used as a preliminary judgment for transformer oil quality and possible faults of transformers. At the same time, according to the different abnormal conditions, we can understand the need to stop the oil chemical monitoring experimental project, in order to make further accurate diagnosis of equipment defects as soon as possible.