In order to improve the insulation strength and dielectric loss coefficient of transformer oil, the transformer oil must be treated before it is injected into the tank to remove moisture, gas and impurities in the oil. In practical application, we have targeted treatment for different types of transformer oil, the effect is better.
1. For transformer oil polluted by impurities such as water and dust, plate-and-frame pressure filters can be used and filtered repeatedly, usually meeting the requirements. Its principle is to use oil filter paper to absorb water and filter impurities. Because of its simple structure and convenient handling, it has also been widely used. The disadvantage is that the filtration is not complete, the removal effect of fine impurities is not good, and the cost is relatively high. When the moisture is large, the oil filter paper needs to be replaced frequently.
2. Vacuum oil filter is widely used nowadays. It can not only completely remove water and gas in oil, but also effectively remove minor impurities. The process flow is as follows: transformer oil to be treated coarse filtration fine filtration vacuum dehydration and degassing of heating oil pure oil. Coarse filtration uses metal filter and strong magnet. Fine filtration usually filters 1 to micron impurities.
At present, there are many kinds of fine filter, such as metal powder sintering material, metal microporous material, ceramic filter material and filter paper with special structure.
Transformer oil is heated and degassed by vacuum dehydration. The principle is to vacuum the oil tank and spray the heated transformer oil to form oil mist, so that the gas and water in the oil escape. Oil temperature is generally around 65 C, not too high, so as not to make the oil aging. The dehydration and degassing effect of this method is better, and it is widely used at present. However, if the oil is sprayed into a very fine mist, it is easy to be pumped away by a vacuum pump.
If the oil is sprayed into oil droplets with a certain diameter, the water and gas in the oil droplets can not be fully utilized due to the high interfacial tension of the oil droplets. For this reason, the diameter of the spray hole should be selected appropriately, and several baffles should be installed at the suction opening of the tank to prevent the transformer oil from being pumped away by the vacuum pump.
3. Treatment of contaminated transformer oil. Polluted transformer oil (commonly known as dirty oil) refers to the colloidal contaminated transformer oil formed by the combination of extremely small impurities and oil molecules, and the transformer oil used for many years, which is generally the oil released from the repaired products (the pH value of this oil is very low). For this kind of waste oil, it must be treated by adsorption to improve the oil index.
In the process of treatment, regular monitoring should be carried out to determine the adsorption effect. When the adsorption effect is not obvious, the replacement of silica gel should be considered. Generally, the amount of silica gel used by weight accounts for about 3%-5% of the oil. The waste oil treatment system should be separated from the new oil treatment system in order to avoid cross-contamination. Tanks and containers that have used dirty oil must be thoroughly cleaned before they can be used in normal production of oil systems.
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