Why is vacuum drying and impregnation necessary for windings?

Drying the winding helps to remove moisture from the insulation components. This not only enhances the insulation's withstand voltage level but also causes the insulation to contract to its inherent dimensions, providing accurate and reasonable data about the winding's axial height and tightening force.

During the drying process of the winding, the following points should be considered: a. Windings that do not require vacuum drying can be processed along with those that require vacuum drying. b. For windings with and without electric wood barrels processed in the same container, the processing should follow the requirements for windings with electric wood barrels. c. The time between the winding coming out of the furnace and immersion in varnish should not exceed 12 hours. If it exceeds 12 to 16 hours, it needs to undergo atmospheric drying at 100 to 115 degrees Celsius for 14 hours. If the storage time is longer, reprocessing is required.

Transformer windings typically use solventless insulation varnish for impregnation, and impregnation is required for windings with U ≤ 40.5kV.

Multi-layered cylindrical windings have a higher number of layer insulation layers, resulting in higher moisture and gas content. To eliminate moisture and gas to ensure proper varnish impregnation, vacuum pressure impregnation is required.

The purpose of impregnating the winding is to increase its mechanical strength. However, not impregnating the winding can increase electrical strength and contribute to better heat dissipation. Therefore, windings of high-voltage transformers (U ≥ 72.5kV) are usually not subjected to impregnation.

After impregnation, preheating should be done at 70 to 80 degrees Celsius for 3 hours, followed by an increase in temperature to 105 to 115 degrees Celsius, maintaining it for 14 hours. For cylindrical windings, it needs to be maintained for 18 hours.

It is noteworthy that the characteristics of coating for dry-type transformer windings are different: for shipboard and tropical dry-type transformer windings, they are typically impregnated with insulation varnish three times, followed by a final spray or immersion in grey varnish. General dry-type transformer windings are usually impregnated twice with insulation varnish.

LuShan, est. 1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 49 years. Leading products are single-phase transformer, three-phase transformers, DC inductors, AC reactors, filtering reactor, expoxy resin high-voltage transformer and intermediate, high-frequency products. Our transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention , excitation system, vacuum sintering, central air conditioning.

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