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Deterioration of Transformer Insulating Oil

July 26,2017.

This paper briefly analyzes the causes and maintenance countermeasures of oil quality deterioration of the transformer oil, analyzes the benefits and economy of the oil regeneration treatment, giveing the regeneration examples of the transformer insulating oil and the problems that should be paid attention to. Help the transformer insulation oil operation and maintenance work.

 

Transformer life is the life of oil and paper insulation systems. Transformer internal solid insulation-cellulosic paper aging and gradual cracking is the result of some chemical reactions within transformers, solid insulation material has irreversible aging characteristics, and in daily operation can’t be maintained. The transformer liquid insulation-oil aging and degradation can be carried out purification and regeneration treatment, and, after purification and regeneration treatment can be the same as the new oil or better. Transformer as one of the key equipment of the power system, the reliability of its operation and the length of life of the power system security, economic and reliable operation plays a decisive role. As the quality of the transformer insulation oil directly affect the quality of the transformer insulation is good or bad, and the transformer insulation is also directly related to the length of the transformer life, therefore, the operation and maintenance of transformer insulation oil work in the power system is particularly important. Do this key work, not only can save energy, save money, environmentally friendly, but also can extend the life of the transformer. 

 

Oil quality classification and test diagnosis of transformer oil

1.1 oil quality classification

Grade oily color acidity interfacial tension/ MN • m-1

The degree of influence on the transformer

1 good light yellow 0.03 ~ 0.10 30 ~ 45 can provide effective cooling, protection of insulation

2 better yellow 0.05 ~ 0.10 27 ~ 30 oil oxide caused by interfacial tension decreased, sludge began to form

3 qualified bright yellow 0.11 ~ 0.15 24 ~ 27 fatty acid covered winding, insulation may be discharged into the oil

4 bad amber 0.16 ~ 0.40 18 ~ 24 core and winding began to have mud deposition, the heat sink surface will be the first deposition of sludge

5 very bad brown 0.41 ~ 0.65 14 ~ 18 deposition of sludge continue to oxidation and hardening, insulation shrink

6 very bad dark brown 0.66 ~ 1.50 9 ~ 14 sludge isolated cooling surface, blocking the oil channel

7 fault black ≥1.51 6 ~ 9 large number of sludge formation

As can be seen from Table 1, the first grade of oil has a variety of excellent indicators; 2,3 grade oil is in the "preventive maintenance" range, belong to a better grade of oil. Although all the functions of this oil can be maintained, but when the interface tension dropped to 27.0mN / m, marking the dissolved state of the sludge has begun to form, it is recommended that the transformer should be overhaul; after the three oil "fault maintenance" Stage of the oil, requiring immediate maintenance treatment; almost all oil for the "bad oil" class transformer internal parts are sludge deposition. Oil level to reach the "fault" level, this time to consider the transformer should be the remaining life and not just is the oil situation.

 

1.2 causes of oil quality deterioration

(1) the impact of operating conditions. Transformers in normal conditions, the oil has a certain degree of oxidation stability, but when the transformer overload or due to local overheating and lead to oil temperature rise, the oil will accelerate the aging of the oil quality will be worse.

(2) the impact of equipment conditions. When the transformer seal is not good, the leakage, leakage will accelerate the oxidation and aging of oil; respirator within the desiccant failure is not timely treatment or oil purification (after the failure of the adsorbent failed to replace And so will promote oil oxidation deterioration; insulation material and oil compatibility is not good, will promote the aging of the oil.

(3) The impact of oil pollution. Insulation caused by the surface of the container is not common pollution, and improper handling of mixed oil can also cause pollution.

(4) The effect of acid and water in the oil. Acid Transformer oil acid value (or neutralization value) to 0.10mgKOH / g has been significantly damaged the transformer fiber (paper), the transformer oil acid value is slow, steady and sustained, and with the oil The degradation of the oil and the insulating material was accelerated with the acid value of 0.2 to 0.5mgKOH / g, accompanied by the formation of sludge, and the photographs of the transformer laminated paperboard at 250 times the electron microscope were shown in Fig. ② water. Oil and cellulose produce water in their own degradation and chemical reactions, which in turn further accelerate the oil

And cellulose degradation, from the external invasion of the transformer water will make the problem more serious. 20 ℃ when the paper on the water affinity than the transformer oil 3000 times, many times the transformer insulation paper water is very high, and the oil is dry, the water involved in the chemical decomposition of paper insulation, water also formed to reduce the paper The effect of dielectric strength, when the water content of dry paper 3%, the cellulose has actually begun in the transformer oil loose and elegant.

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