Can transformer oil be regenerated?

Transformer oil can be regenerated, but the appropriate regeneration method should be selected according to the degree of oil aging and pollution type. The purpose of regeneration is to restore the insulation performance, chemical stability and physical properties of the oil and extend its service life. The following are detailed methods and precautions for transformer oil regeneration:

1. Applicable conditions for transformer oil regeneration

1. Regenerable oil products:

- High moisture content (≤500ppm).

- Slightly increased acid value (≤0.3mg KOH/g).

- Dielectric loss factor (tanδ) ≤2%.

- Contains mechanical impurities, colloids or soluble pollutants.

2. Situations where oil needs to be changed:

- Deep oxidation of the oil (acid value > 0.5mg KOH/g).

- Severe carbonization or containing a large amount of irreversible aging products (such as sludge).

- The breakdown voltage cannot be restored for a long time (<30kV).

Transformer oil regeneration method

1. Physical purification method (mild pollution)

- Method: Remove impurities and moisture by filtration, centrifugation, or vacuum dehydration.

- Equipment: vacuum oil filter, centrifugal oil filter.

- Applicable: Oil contains water and solid particles, but not severely oxidized.

Adsorption regeneration method (moderate pollution)

- Adsorption materials:

- Activated white clay: adsorption of colloids and acidic substances (subsequent filtration is required).

- Silica gel/molecular sieve: removal of moisture and polar compounds.

- Activated alumina: deacidification and decolorization.

- Operation method:

- Direct addition: Add the adsorbent to the oil and stir and filter (suitable for small equipment).

- Circulation adsorption: Circulation treatment through the adsorption tower (industrial regeneration).

3. Chemical regeneration method (severe aging)

- Method:

- Alkaline washing: neutralize the acidic substances with sodium hydroxide solution (subsequent water washing and vacuum dehydration are required).

- Solvent extraction: Use solvents such as propanol to dissolve aging products (specialized equipment is required).

- Note: After chemical regeneration, the residual reagents must be completely removed to avoid affecting the insulation performance.

4. Electrostatic regeneration method (high precision requirements)

- Principle: Use an electrostatic field to separate colloidal particles and polar pollutants.

- Applicable: Deep purification of ultra-high voltage transformer oil.

5. Combined regeneration process

- Typical process:

Vacuum dehydration → precision filtration → adsorption treatment → electrostatic purification

- Effect: The oil quality can be restored to a level close to the new oil standard.

Regeneration operation steps (taking the adsorption method as an example)

1. Sampling and testing: Clarify the aging indicators of the oil (acid value, moisture, tanδ).

2. Pretreatment:

- Vacuum dehydration to moisture < 10 ppm.

- Filter to remove solid particles (precision ≤5μm).

3. Adsorption regeneration:

- Add activated clay (3%~5% oil weight) to the oil and stir at 60℃ for 2~4 hours.

- Filter to remove the adsorbent (filter element accuracy ≤1μm).

4. Post-treatment:

- Vacuum degassing (remove residual air).

- Re-inject into the transformer after the test indicators are qualified.

Performance verification of regenerated oil

The regenerated oil must meet the GB/T 7595-2017 "Quality of Transformer Oil in Operation" standard:

| Indicators | Requirements |

|------------------|-------------------------|

| Moisture | ≤10ppm (ultra-high voltage ≤5ppm) |

| Acid value | ≤0.1mg KOH/g |

| Breakdown voltage | ≥50kV (new oil ≥60kV) |

| Dielectric loss factor | ≤0.5% (90℃) |

Precautions

1. Safety risks:

- Harmful gases (such as hydrogen sulfide) may be released during the regeneration process, and ventilation protection is required.

- Heating temperature ≤65℃ to prevent oil cracking.

2. Economic evaluation:

- If the regeneration cost is greater than 70% of the new oil price, it is recommended to change the oil directly.

3. Transformer protection:

- During regeneration, the transformer insulation must be protected from moisture (dry nitrogen can be filled for protection).

Suggestions for extending the life of transformer oil

- Regular monitoring: Check moisture, acid value and breakdown voltage every 6 months.

- Sealed system: Use a nitrogen seal or a dry respirator.

- Online purification: Install an electric oil filter (such as a CJC system).

Transformer oil regeneration is an option, but the appropriate method should be adopted according to the degree of contamination. Penetrating contamination can be restored by vacuum oil filtration and adsorption, while deep-aged oil requires professional chemical regeneration or oil replacement. Always follow the standards when operating to ensure that the regenerated oil meets the insulation requirements!