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Why Dehydration And Filtering Of Transformer Oil Is Important

Why Dehydration And Filtering Of Transformer Oil Is Important

why <a href= target='_blank'>Transformer Oil Filter</a>ing is important

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 insulation strength will be reduced; and the oil is in contact with oxygen during transportation and operation, and it is easy to oxidize and deteriorate at high temperatures. Therefore, transformer oil filtration should be carried out during transformer installation and daily maintenance.

In order to prevent the safe operation of the transformer from being threatened due to the deterioration of the oil quality, the regular oil samples of the power distribution in normal operation should be tested and analyzed, and the oil should be treated according to the analysis results. 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 amount 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

The water-soluble acid limit value of transformer oil is less than 4.2. There are 2 possible reasons for exceeding the limit value: oil aging; 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 (Dielectric strength)

Its ultra-limit value is less than 20kV. There are two possible reasons for exceeding the limit value: the water content in the oil is too large; the oil is polluted by impurity particles. 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 with 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: the equipment has a local overheating fault; the wrong oil is supplied. 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. Outer shape (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, fibers, 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 has changed obviously, it should be noted 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.


Therefore, in the daily maintenance of transformers, the filtration of transformer oil is also a very important part of the maintenance work. Transformer maintenance engineers should use vacuum transformer oil filtration machine or Transformer Oil Regeneration plant to purify transformer oil by removing moisture in the oil , gases and impurities, and even oxidation products such as acids. Note also that new oil needs to be filtered before being injected into the transformer. Transformer Oil Filtering keeps the transformer in good condition and increases its life.


More details about transformer oil filtering please contact us PureTech Oil Filtration team.


PureTech Oil Filtration


Tel: +86 17815389416 WhatsApp


 transformer oil filtering should be done when transformer installation

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