What are the purposes of transformer oil filtration?

Transformer oil filtration is a key process in power equipment maintenance. Its main uses include performance recovery, safety protection, environmental protection and energy saving, as follows:

Restore insulation performance

- Remove moisture:

Moisture will greatly reduce the dielectric strength (breakdown voltage) of the oil. After filtration, the moisture content can be reduced from 50 ppm to ≤ 10 ppm (IEC 60422 standard) to prevent internal discharge.

- Remove particulate matter:

Filter out impurities such as metal chips and fibers (the filtration accuracy can reach 1-3 microns) to avoid short circuits between conductors.

Extend the life of oil products

- Remove aging products:

Filtration can remove acids and sludge generated by oil oxidation (the acid value is reduced from 0.5mg KOH/g to less than 0.1mg), delaying oil deterioration.

- Adsorption purification:

Silica gel or molecular sieves can remove soluble polar compounds (such as sulfides) and restore the chemical stability of the oil.

Ensure safe operation of equipment

- Prevent failure:

Moisture and particulate matter can cause local overheating or arcing. After filtering, the transformer failure rate is reduced (such as the risk of winding breakdown is reduced by more than 60%).

- Gas control:

Vacuum oil filtration can remove dissolved gases (H₂, CH₄, etc.) and inhibit insulation failure caused by the bubble effect.

Energy saving and environmental protection

- Waste oil regeneration:

Severely aged oil can be re-reached by deep filtration (such as clay adsorption) to meet the new oil standard (by GB/T 7595) and reduce waste oil emissions.

- Reduce loss:

The dielectric loss factor (tanδ) of clean oil is ≤0.005 (at 90℃), which reduces energy loss by about 30% compared with contaminated oil.

Special scenario application

- New oil pretreatment:

New oil may contain trace amounts of moisture and particles. Injecting it into the equipment after filtering can avoid initial contamination.

- Inspection and maintenance:

When inspecting the transformer cover, filtering the oil can avoid rework contamination (such as purification before vacuum oil filling).

Adapt to extreme environments

- Alpine areas:

The oil condensation point after filtration is ≤- -45℃ (such as silicone oil-based insulating oil) to ensure low-temperature fluidity.

- Hot and humid climate:

Deep dehydration can prevent oil hydrolysis caused by tropical environmental humidity.

Industry standard reference

- International: IEC 60422 (Guidelines for the maintenance of mineral insulating oil)

- Domestic: GB/T 7595-2017 (Oil quality of operating transformers)

- Test indicators: breakdown voltage ≥50kV (new oil ≥60kV), moisture ≤15ppm, acid value ≤0.1mg KOH/g.

Operation precautions

- Pre-filtration detection: The moisture and gas content in the oil must be measured first (such as chromatographic analysis) to ｓｅｌｅｃｔ the appropriate process.

- Equipment matching: Ultra-high voltage transformers above 500kV need to ｓｅｌｅｃｔ filter elements with a precision of ≤1 micron + vacuum degassing.

- Anti-secondary pollution: The oil should be stored in a sealed manner after filtration to avoid contact with air and moisture absorption.

Through systematic filtration, transformer oil can maintain a "clean-dry-low-gas" state for a long time, directly extending the equipment life (average extension of 5-8 years) and reducing operation and maintenance costs.