Gianfranco

Standard steps include preparing the transformer and ensuring dryness, pulling vacuum on the tank to remove air and moisture, filtering and degassing the oil, filling under vacuum to avoid entrapped bubbles, monitoring level and temperature, then sealing and verifying leaks. After filling, the oil is allowed to stabilize and samples may be taken for BDV and moisture. Procedures vary for conservator vs sealed units and for on site vs factory fill.

Transformer oil is an insulating liquid used to electrically insulate energized components and remove heat from the transformer core and windings. It also suppresses electrical arcing, protects insulation from oxidation, and transfers heat to cooling surfaces. Together, these functions ensure safe operation, long service life, and reliable performance under load.

A BDV kit applies a controlled AC voltage across two standardized electrodes immersed in the oil sample. Voltage is ramped until breakdown occurs, and the breakdown voltage is recorded, usually with multiple repeated shots to get an average. The method controls electrode gap, rise rate, and stirring conditions to reduce randomness. IEC 60156 is a widely referenced method for the breakdown voltage test approach.

Transformer oil density is the mass per unit volume and it decreases as temperature increases because the oil expands. This matters for volume calculations, conservator sizing, oil level indications, and logistics such as transport and tank filling. Density also influences buoyancy driven oil circulation in natural cooling modes. Specifications usually list density at a reference temperature, often 15 degrees Celsius, and provide correction factors or charts. For accurate operating condition estimates, use the supplier data sheet and apply temperature correction.

Oil provides a combined insulation and cooling medium that allows compact, high voltage designs with strong dielectric margins. It fills internal spaces, excludes moisture laden air, and raises breakdown strength between windings and to ground. Thermally, oil absorbs heat from windings and carries it to radiators, preventing hot spots that accelerate paper aging. Stable temperatures and dry insulation reduce partial discharge and arcing risk. Without oil, equivalent high voltage and high MVA transformers would require larger clearances or different insulation systems, often with higher cost or lower performance.