How to deal with impurities in transformer oil?

Transformer oil impurity treatment plan

Impurities in transformer oil (such as metal particles, fibers, dust, carbides, etc.) will affect the insulation performance of the oil, accelerate equipment aging, and even cause failures. The following is a systematic treatment method, covering mechanical filtration, vacuum purification, adsorption treatment and other technologies to ensure that the oil is restored to a high cleanliness level.

1. Analysis of impurity types and hazards

| Impurity types | Source | Hazards |

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

| Solid particles (metal shavings, dust) | Equipment wear, installation residues | Wear of insulating paper, blockage of oil channels |

| Fiber impurities (paper scraps, cotton wool) | Aging of insulating materials | Reduce dielectric strength and cause partial discharge |

| Carbides (arc products) | Internal discharge or overheating | Conductive, leading to oil degradation |

| Gel-like substances (oil sludge) | Oxidation aging products | Block heat dissipation channels and affect cooling |

2. Steps for treating transformer oil impurities

(1) Preliminary detection

- Visual inspection: Observe the oil color (normal is light yellow, black/turbid indicates serious pollution).

- Laboratory testing: Measure key indicators such as particle size (NAS grade), dielectric strength (kV), and acid value.

(2) Pretreatment (coarse filtration)

- Equipment: plate and frame oil filter, centrifugal oil filter

- Filter element accuracy: 20~50μm (remove large particles)

- Applicable situation: Used when the oil contains a large amount of visible impurities.

(3) Deep filtration (precision treatment)

- Equipment: vacuum oil filter (with precision filtration system)

- Filter element accuracy: 1~5μm (remove tiny particles)

- Technology combination:

- Mechanical filtration → Remove solid particles

- Vacuum dehydration → Remove water and gas

- Coagulation separation → Treat emulsified impurities

(4) Adsorption treatment (remove colloid/carbonate)

- Method:

- Activated clay adsorption: Applicable to colloidal substances and acidic impurities.

- Silica gel/molecular sieve: Adsorb trace moisture and polar impurities.

- Note: After adsorption, it is necessary to filter again to avoid residual adsorbent.

(5) Final inspection and re-injection

- Inspection standards:

- Cleanliness: NAS 5~6 (ISO 4406)

- Dielectric strength: ≥50kV/2.5mm (new oil standard)

- Water content: ≤10ppm (UHV transformers have stricter requirements)

- Re-injection transformer: adopt closed circulation to prevent secondary contamination.

3. Treatment solutions for different pollution levels

| Pollution level | Recommended treatment methods |

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

| Mild pollution (NAS 8~9) | Precision filtration (1~5μm) + vacuum dehydration |

| Moderate pollution (NAS 10~12) | Centrifugal separation + vacuum oil filtration + adsorption treatment |

| Severe pollution (NAS >12 or more sludge) | White clay adsorption regeneration + multi-stage filtration |

| Contains carbides (arc pollution) | Special carbon adsorption filter element + vacuum degassing |

4. Key equipment recommendations

1. Plate and frame oil filter → coarse filtration (20~50μm)

2. Vacuum oil filter → Precision filtration + dehydration and degassing

3. Centrifugal oil filter → Treatment of oil with high impurity content

4. Coagulation separation system → Treatment of emulsified oil

5. Precautions

- Safe operation: Keep away from fire when filtering oil and avoid excessive oil temperature (≤70℃).

- Environmental protection requirements: Waste oil and filter elements should be treated according to hazardous waste standards.

- Regular maintenance: It is recommended to filter the oil 1~2 times a year during transformer operation, or monitor the oil quality online.

Transformer oil impurity treatment should ｓｅｌｅｃｔ a combination of mechanical filtration, vacuum purification, adsorption regeneration and other processes according to the type and degree of pollution, ultimately ensuring that the oil reaches high cleanliness (NAS 5~6 level), low moisture (≤10ppm), and high dielectric strength (≥50kV). Regular maintenance can greatly extend the life of the transformer and prevent failures!