Transformer oil is the main insulation and cooling medium of oil-immersed transformers. Its electrical strength and chemical composition directly affect the performance of transformers. If the oil contains a small amount of water and impurities, the dielectric strength will be reduced; and the oil is easily oxidized and deteriorated at high temperatures when it is in contact with oxygen. Therefore, the transformer oil should be filtered when the transformer is installed.
To prevent the impact on the safe operation caused by oil quality deterioration, regular oil samples from power distribution in normal operation should be tested and analyzed, and the oil should be treated according to the results of the transformer oil test and analysis. The inspection cycle of oil chemical supervision for power distribution operation is stipulated to be at least once every 3 years.
1. Acid value
The acid value is the number of acidic substances contained in the oil, and the number of milligrams of potassium hydroxide required to neutralize the acidic substances in 1g of oil is called the acid value. Acid value includes both organic and inorganic acids contained in the oil, but in most cases the oil does not contain mineral acids. Therefore, the oleic acid number actually represents the amount of organic acids in the oil. The organic acid contained in new oil is mainly cycloacid. During storage and use, the organic acids produced by oil oxidation are fatty acids. For new oil, the acid value is a sign of the degree of refinement, and for operating oil, it is a sign of the degree of oil aging, and is one of the important indicators to determine whether the oil can continue to be used.
2. Water-soluble acid
Its ultra-limit value is less than 4.2. There are two possible reasons for exceeding the limit value: one is oil aging; the other is oil contamination. The following countermeasures can be taken for water-soluble acid exceeding the limit value: increase the number of tests, and compare with the acid value to find out the reason. Carry out oil regeneration treatment, if economical and reasonable, oil change treatment can be done.
3. Breakdown voltage
Its ultra-limit value is less than 20KV. There are two possible reasons for exceeding the limit value: one is that the water content in the oil is too large; the other is that there are impurity particles in the oil. The following countermeasures can be taken if the breakdown voltage exceeds the limit value: find out the cause, carry out vacuum oil filter treatment, plate and frame pressure oil filter treatment or replace new oil. Generally, ZJB vacuum filter oil is used, and the breakdown voltage of the oil after treatment is required to be greater than 50KV.
4. Flash point
Its ultra-limit value is less than 130°C. Or drop 5°C from the previous test value. There are two possible reasons for exceeding the limit value: one is that the equipment has a local overheating fault; the other is that the wrong oil has been added. The following countermeasures can be taken if the flash point exceeds the limit value: find out the cause and eliminate the fault; degas the vacuum oil filter or change the oil.
5. Appearance
If the appearance is visually opaque, there are visible impurities or suspended matter. Or if the oil color is too dark, the appearance of the oil is abnormal. The possible causes of abnormal appearance are: the oil contains moisture, fiber, carbon black and other solids. The following countermeasures should be taken for oil with abnormal appearance: If the oil is cloudy, turbid and whitish, it indicates that the oil contains water, and the water content should be checked. If it is found that the oil contains carbon particles, the oil color is black, or even has a burnt smell, it may be that there is an arc or partial discharge fault inside, and it should be combined with other tests to investigate the cause and eliminate the fault. If the color of the oil is dark and the color of the oil changes significantly, attention should be paid to whether the aging of the oil is accelerated, which can be combined with the acid value test analysis of the oil, or the monitoring of the operating temperature of the oil should be strengthened.
