VPD (Vapour Phase Drying) — Transformer Glossary

Advanced drying process using kerosene vapour under vacuum to remove moisture from transformer insulation to levels below 0.5%.

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VPD (Vapour Phase Drying)

Advanced drying process using kerosene vapour under vacuum to remove moisture from transformer insulation to levels below 0.5%.

VPD is superior to conventional hot-air drying (which typically achieves 1–1.5% moisture). The process: (1) active components placed in autoclave, (2) kerosene vapour condensed on cold insulation surfaces, heating uniformly, (3) vacuum applied to extract moisture. Benefits: lower moisture content = higher dielectric strength, longer insulation life, better impulse withstand. VPD is essential for power transformers rated above 33 kV. ETS operates a dedicated VPD autoclave facility at its Dubai manufacturing plant.

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Insulation ClassClassification of insulation materials based on their maximum continuous operating temperature. Determines the transformer's thermal endurance.

Partial Discharge (PD)Localised electrical discharge that does not fully bridge the insulation between conductors. A precursor to insulation failure.