Due to the high requirements for the quality of transformer oil, strictly speaking, it is difficult to determine whether the quality of the oil is qualified without a simplified test, but the unqualified oil can sometimes be judged from the appearance.
(1) The color of the oil. The new oil is generally light yellow, and the color becomes darker after oxidation. If the new oil is dark and dark, it is unqualified. The color of the oil darkens rapidly during operation, indicating deterioration of the oil quality.
(2) Transparency. The new oil is transparent and has purple fluorescence in the glass bottle. If the fluorescence is lost or the transparency is reduced, it means that it contains mechanical mixture and free carbon.
(3) Odor. The new oil has a slight kerosene smell, if there are other smells, the oil quality has deteriorated. If there is a burning smell, it means the oil is overheated; if there is a sour smell, it means the oil is seriously aging; the acetylene smell means that an electric arc has been generated in the oil; other smells are produced with the container.
3 Operating requirements for transformer oil
When transformer oil is in operation, if it contacts the air, it will get damp. This unfairly reduces the breakdown voltage and increases the dielectric loss, and enhances the corrosion catalysis of metals, causing the formation of deposits in the oil. It is generally believed that the deteriorated oil is more susceptible to moisture than new oil, and the deterioration rate is 2-4 times faster. If it is found that most of the silica gel has changed from the original blue to red or purple, it means that the desiccant has failed, and the dried silica gel should be replaced.
Since the transformer oil is in operation, it will gradually age due to the influence of air, sunlight, humidity and temperature, so it is necessary to take active measures to keep it in good condition as far as possible to prolong its service life. At present, the following measures are generally adopted in actual production.
One oxygen protection
Use inert nitrogen to fill the upper space of the transformer oil conservator, so that the oil is always in contact with the nitrogen, so the transformer oil is isolated from the air, which can prevent premature aging of the oil.
Second-use oil purifier
The oil purifier is a metal container filled with adsorbent (in addition to acid silica gel or activated alumina). When transformer oil flows through the adsorbent, the moisture in the oil, free acid, and oxides that accelerate the aging of the insulating oil are all absorbed by the adsorbent. Absorbed, the oil is continuously regenerated, and the oil quality can remain qualified for a long time. According to the different ways the oil flows in the oil purifier, it can be divided into two categories. Temperature difference circulation method oil purifier and forced circulation method oil purifier
(1) Selection and dosage of adsorbent
The adsorbent should have the characteristics of porous, strong activity, strong acid absorption, etc., in order to absorb water, peroxy compounds, organic acids, carbonyl groups and other substances harmful to the transformer and oil in the oil. There are only two kinds of acid-removing silica gel (coarse and fine pore silica gel) and activated alumina that are generally used with better effects and are cheap. They are spherical and rod-shaped irregular porous solid substances. Their performance has the following requirements:
①Water absorption rate>20%
②Acid absorption>5mg(KOH)/g (silica gel);
④ The appearance is milky white.
Therefore, the adsorbent should be dried and sieved before being added to the oil purifier.
The amount of adsorbent is determined by the total mass of oil. When using deacidified silica gel, it is about 0.75% to 1.25% of the total oil mass. Smaller capacity transformers use large numbers; large capacity transformers use small numbers. When activated alumina is used, it is about 0.5% of the total oil mass.