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Moisture Content in Transformer Oil and Insulation Paper

Moisture Content in Transformer Oil and Insulation Paper

Can the level of moisture content in transformer oil determine the dryness of the insulation?

The moisture in the oil is in a balanced state with the insulating paper. Insulating oil has different saturated water solubility at different temperatures, and it increases with the increase of temperature. Therefore, the water in the insulating paper enters the oil at high temperatures; when the oil temperature drops, part of the water in the oil will be transferred to the paper.

moisture content in transformer oil

Such water diffusion reduces the moisture content in transformer oil. Generally speaking, the higher the operating temperature, the more the water in the paper diffuses into the oil, so the water content in the oil increases. But it must be pointed out that the equilibrium state of water between oil and paper is not a static equilibrium, but a dynamic equilibrium.

However, achieving this balance requires a longer process. Therefore, it is not possible to confirm or deny the moisture content of the transformer from the amount of water in the oil, especially when the ambient temperature is very low and the transformer is in a shutdown state and the water content in the oil is measured to be very low, it cannot be used as transformer insulation. The only criterion for dryness. On the contrary, when the operating temperature of the transformer is high (not a short rise), the water content in the measured oil is very low, which can be used as one of the basis for good insulation.

In the transformer installation, repair and routine maintenance process, we will conduct transformer oil testing. When the oil sample is unqualified, we should immediately arrange for transformer oil filtration and vacuum drying. By using the PureTech Double-Stage High Vacuum Transformer Oil Filtration Machine, you can achieve below oil data after purification.

Oil Parameters Before Purification After Purification
Moisture Content (ppm) 50 - 100 < 5
Gas Content (%) 10 < 0.1
Particulate Size (micron) 50 1
Breakdown Voltage (KV) 10 - 20 > 75

PureTech supplys Transformer Oil Purifier with different capacities, flow rate ranges from 600 liters/hour to 18000 liters/hour. Transformer Oil Filtration Machine mainly adopts the technology of thermal-vacuum dehydrating and degassing, as well as filtration, to effectively remove contaminants from transformer oil, reduce the moisture in transformer oil, improve the breakdown voltage / dielectric strength of transformer oil. The transformer oil filtration procedure please kindly check product details.

transformer oil filtration machine to reduce moisture content in transformer oil