Requirement of Purifying Adsorbent for Transformer Oil Operation

- Dec 17, 2020-

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);

        ③Water content<0.5%;

        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.

        (2) Management of oil purifier in operation

        In order to grasp the failure time of the adsorbent in time, it is necessary to regularly sample the oil in the oil purifier. The usual method is to close the oil purifier, isolate it for a day and night, and then take the oil from the transformer body and the oil purifier at the same time. In the same way, the acid value is measured. If it is close to failure, the acid value of the two is similar; if it has not failed, the acid value in the oil purifier is much lower than that in the transformer body.

        Antioxidant added to three oils

        Adding antioxidants to the oil can prevent and delay the deterioration of the oil. At present, the antioxidant usually added is 2.6-di-tert-butyl p-methylphenol. It is based on the interaction between antioxidant molecules and free radicals to interrupt the oxidized melon chain to inhibit oil oxidation.

        The amount of oxidant added is about 0.3% to 0.5% of the total mass of the oil. But antioxidants must be added to the oil when the oil is in the initial oxidation stage, or before this stage, in order to effectively prevent the oxidation of the oil. When the oil has been deeply oxidized, adding antioxidants has little effect. However, antioxidants have been added to the new oil when it leaves the factory.

        As the transformer runs for a long time, the oxidizing agent in the oil is gradually consumed, and the content of antioxidants gradually decreases, so the oxidizing ability is gradually weakened. Only when the concentration of antioxidants in the oil is maintained within a certain range, for example, about 0.3%, can the oil be oxidized. Therefore, it is necessary to regularly sample the oil in the transformer body to determine the concentration of its antioxidants. Once it is found that its concentration has dropped below a certain limit, it must be added in time to always maintain its antioxidant capacity.