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Vacuum in the manufacture of transformers, isolators and high-voltage switchgear

Power transformers are needed to transfer energy from power plants or public electricity networks to the consumer. They regulate electricity voltages and flows upwards and downwards to transfer energy cost-efficiently and to provide the necessary voltages. In the manufacture of these transformers, vacuum technology is required at various stages of the production process:

for drying windings, for degassing transformer insulating oil and for evacuating the transformer tank and expansion vessel before and during the oil filling process.

Drying windings
The aim of the drying windings is to remove water, tannic acid and acetic acid from paper and wood and to remove polymers as well as wax from the paper insulation. In high-performance transformers, the potential for flashovers dictates that the residual moisture content must not exceed 0.1 – 0.3 percent. This is to prevent the occurence of flashovers. As a result, electrical losses are reduced to a minimum and the insulation resistance is improved. In the vacuum range of 0.1 – 10-2 hPa, the insulation resistance is at an ideal level for the actual application. The vacuum required for drying the windings is generated with a combination of Roots pumps and rotary vane pumps. If the application is a clean one, dry pumps are used as backing pumps for the Roots pumps. There are different principles available for drying the windings. The most effective procedure is vapor phase drying (VPD).

Pfeiffer Vacuum drying pumping stationFig.1: Pfeiffer Vacuum drying pumping station

Read more about this state of the art technology in the attached application report.

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