What are the insulating oil filtration equipment?

There are many types of filtering equipment for insulating oil (including transformer oil, switch oil, etc.). According to different purification requirements (such as dehydration, degassing, impurity removal, etc.), the commonly used equipment mainly includes the following categories:

1. Vacuum oil filter (high-efficiency dehydration and degassing)

Applicable scenarios: deep removal of moisture, gas and fine particles, suitable for high-voltage/ultra-high-voltage transformer oil treatment.

Working principle:

- Heating system: oil temperature is controlled at 50~65℃ (promote moisture evaporation).

- Vacuum system: separate moisture and gas under high vacuum (≤ 50 Pa).

- Precision filtration: multi-stage filter element (1~5 μm) intercepts particulate impurities.

Features:

- Moisture can be reduced to ≤5 ppm, gas content ≤0.1%.

- Breakdown voltage is increased to ≥60 kV.

2. Pressure oil filter (particle filtration)

Applicable scenarios: remove solid impurities and a small amount of moisture, suitable for medium and low voltage equipment, or the retreatment stage.

Working principle:

- Multi-stage filter element: filtration in stages (10 μm → 5 μm → 1 μm).

- Pressure drive: pressurize the oil through the filter material by pump (0.3~0.6 MPa).

Features:

- Cleanliness can reach NAS 1638 Class 6 (ISO 4406 15/12/9).

- Weak dehydration ability, needs to be used in conjunction with other equipment.

3. Centrifugal oil filter (large flow impurity separation)

Applicable scenarios: Rapid removal of free water and large particle contaminants (such as metal chips, oil sludge).

Working principle:

- High-speed centrifugation: Separate water and particles by density difference (no filter element required).

Features:

- Large processing capacity (up to 10,000 L/h), but low precision (≥5 μm).

- Suitable for preliminary purification of oil products or pretreatment of waste oil regeneration.

4. Coalescing and dehydrating oil filter (specializing in emulsified water)

Applicable scenarios: treatment of insulating oil with severe emulsification (water in suspension).

Working principle:

- Coalescing filter element: merge tiny water droplets into large droplets and then separate.

- Vacuum assistance: further remove free water.

Features:

- Can handle emulsified oil with water content ≤100 ppm, and ≤10 ppm after dehydration.

5. Electrostatic oil purifier (ultra-precision purification)

Applicable scenarios: removal of submicron particles (0.1~1 μm) and colloidal substances.

Working principle:

- High-voltage electrostatic field: adsorbs charged particles and colloids.

Features:

- Cleanliness can reach NAS Class 3~4 (close to new oil standards).

- Usually used as terminal fine filtration equipment.

6. Adsorption oil filter (chemical pollutant removal)

Applicable scenarios: removal of acid value, oxides or soluble impurities.

Working principle:

- Adsorbent: activated alumina, silica gel or molecular sieve.

Features:

- Can reduce acid value to ≤0.01 mg KOH/g and extend oil life.

7. Online oil filter system (continuous maintenance)

Applicable scenarios: real-time purification of oil products during transformer operation.

Composition:

- Combined design (such as vacuum + pressure + adsorption).

Features:

- Maintain oil quality stability and reduce the frequency of shutdowns and maintenance.

Selection Recommendations

| Requirements | Recommended Equipment |

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

| Deep Dehydration and Degassing (500kV+) | High Vacuum Oil Filter |

| Rapid Impurity Removal (Maintenance Site) | Pressure Oil Filter + Centrifugal |

| Emulsified Oil Treatment | Coalescing and Dehydrating Oil Filter |

| Ultra-precision Purification (UHV) | Electrostatic Oil Purifier + Adsorption |

| Maintenance During Operation | Online Oil Filter System |

Notes

1. Temperature Control: All heating equipment must ensure that the oil temperature is ≤65℃.

2. Filter Element Grade: ｓｅｌｅｃｔ the filtration accuracy according to the target cleanliness (such as NAS Class).

3. Compatibility: Avoid reactions between adsorbents or filter materials and additives in the oil.

By combining the above equipment, the full-scenario insulation oil purification needs from daily maintenance to fault recovery can be met.