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
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