Adverse effects of moisture on transformer oil
1. Moisture significantly impacts the physical, chemical, and electrical properties of transformer oil.
- Moisture will reduce the breakdown voltage of the oil. According to reports, the breakdown voltage is about 15kV when the water content in the oil is 0.01%. When the water content was increased to 0.03%, the breakdown voltage dropped to about 6kV.
- Moisture will affect the dielectric loss factor. As moisture increases, so does the dielectric loss factor. When the water content in the oil is 0.02%, the dielectric loss factor is 1×10-6. When the water content increases to 0.1%, the dielectric loss factor increases to 2.1×10-6.
2. Moisture will promote the corrosive effect of organic acids on metals such as copper and iron. The subsequent saponification will deteriorate the dielectric loss factor of the transformer oil, increase the moisture absorption of the oil, and catalyze the oxidation of the oil. It is generally believed that the aging rate of damp oil is 2-4 times faster than that of dry oil.
3. The trace moisture in the transformer oil will greatly reduce the insulation performance of the equipment, accelerate the aging of the insulation system, and also lead to partial discharge breakdown of the transformer and the generation of air bubbles. This not only shortens the normal service life of the transformer but also leads to major accidents such as insulation breakdown and equipment burning in severe cases.
The state of slight water in transformer oil
During transportation, storage, and use of transformers, water may be generated due to external entry or self-oxidation of oil. The moisture produced has these forms:
Free water is mostly water intruded from the outside world. Since water is heavier than oil, when the interfacial tension of the transformer oil is 30-50 mN/m, the water immersed in the equipment will quickly flow to the bottom of the transformer. If the free water is located where there is no access to the transformer insulation system, it flows down the side walls of the transformer without splashing onto the transformer core and windings. Although the oil is in close contact with the free water at the bottom of the transformer, it does not affect the breakdown voltage of the oil and is still relatively harmless to the transformer. But it is also not allowed and should be dealt with immediately.
Fine particles dissolve in water
When new transformer oil does not contain mechanical impurities, the water suspended in the oil will quickly settle to the bottom of the tank. When the oil contains oxidation products, fibers, and other mechanical impurities, water tends to stick to these impurities. At this time, the interfacial tension between oil and water will decrease sharply. The oxidation products in transformer oil are mostly hydrophilic surface-active substances, which continuously absorb water. As a result, this heavier suspension, which has absorbed moisture, circulates with the oil flow in the transformer and enters the fiber insulation or areas of high electric field strength, causing the insulation resistance to drop.
The interfacial tension between oil and water will be reduced due to poor refining of oil, aging of oil due to long-term operation, or contamination of the oil by emulsion. If oil and water are mixed together, they will form an emulsified state.
Transformer oil can absorb moisture from the air. The moisture absorption of transformer insulating oil is related to the chemical composition of the oil (especially the aromatic hydrocarbon content), the relative humidity, and the temperature of the air.
What is vacuum transformer oil dehydration?
The vacuum transformer oil dehydration machine developed and manufactured by YUNENG is suitable for treating old and new transformer oil containing moisture, particles, gas, impurities, and acidic substances. It can effectively and quickly eliminate the acid, moisture, dissolved gases, and particulate matter in insulating layers. The machine can effectively solve the problem of transformer oil dehydration.
If you want to know more about transformer oil dehydration knowledge or products, please feel free to contact us.