What are the methods of transformer oil filtration?

There are several main methods for filtering transformer oil. Choose the appropriate method according to different pollution types and treatment targets:

1.Mechanical filtration (pressure oil filtration)

- Principle: Physically intercept particulate impurities (such as metal chips, dust, etc.) through filter paper or filter element.

- Equipment: Plate and frame pressure oil filter, filter element oil filter.

- Applicable scenarios:

- Remove solid particles (above 5μm).

- Mild water pollution (filter paper can absorb a small amount of water).

- Advantages: simple operation and low cost.

- Disadvantages: Cannot dehydrate or degas deeply, and filter materials need to be replaced frequently.

2. Vacuum oil filtration (vacuum dehydration and degassing)

- Principle: Heat the oil in a vacuum environment to evaporate and separate water and gas.

- Equipment: vacuum oil filter (with heating system).

- Applicable scenarios:

- Deeply remove water (can be reduced to below 10 ppm).

- Remove dissolved gases (such as oxygen and nitrogen).

- Advantages: efficient dehydration, fast oil quality recovery.

- Disadvantages: complex equipment, high energy consumption.

3. Centrifugal separation

- Principle: use centrifugal force to separate impurities of different densities (such as water, metal particles) from oil.

- Equipment: centrifugal oil filter.

- Applicable scenarios:

- Large amounts of free water or heavy particle pollution.

- No filter material required, suitable for the pretreatment of highly polluted oil.

- Advantages: large processing volume, suitable for coarse filtration.

- Disadvantages: unable to remove dissolved water or micron-sized particles.

4. Adsorption purification (molecular sieve/silica gel)

- Principle: use adsorbents (such as silica gel, activated alumina) to remove trace moisture and acidic substances.

- Equipment: adsorption tower or online adsorption device.

- Applicable scenarios:

- Deep drying (when the water content requirement is extremely low).

- Reduce acid value (adsorb aging products).

- Advantages: high precision, can handle soluble pollutants.

- Disadvantages: adsorbent needs to be replaced regularly, and the cost is high.

5. Electrostatic oil filtration (electrostatic adsorption)

- Principle: a high-voltage electrostatic field charges and adsorbs colloidal particles charged and adsorbed.

- Equipment: electrostatic oil filter.

- Applicable scenarios:

- Remove colloidal substances (such as carbides, colloidal water).

- Advantages: no heating is required, suitable for heat-sensitive oil products.

- Disadvantages: ineffective for free water and large particles.

6. Hot oil circulation (transformer live oil filtration)

- Principle: extract oil from the bottom of the transformer, heat it after filtering and circulate it back to the top.

- Equipment: vacuum oil filter + heating system.

- Applicable scenarios:

- Maintenance of the transformer without a power outage.

- Combined with vacuum dehydration.

- Advantages: reduce power outage losses.

- Disadvantages: strict monitoring of oil temperature and transformer operating status is required.

7. Chemical regeneration (acid washing/alkaline washing)

- Principle: Remove acidic substances and aging products through chemical reagents (such as clay, sulfuric acid).

- Applicable scenarios:

- Severely aged oil (acid value > 0.5mg KOH/g).

- Advantages: Can restore some chemical properties of the oil.

- Disadvantages: Complex process, requires subsequent fine filtration.

Selection basis

| Pollution type | Recommended method |

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

| Solid particles | Mechanical filtration, centrifugal separation |

| Free water | Centrifugal separation, vacuum oil filtration |

| Dissolved water/gas | Vacuum oil filtration, adsorption purification |

| Colloidal pollutants | Electrostatic oil filtration |

| Acidic substances/aging products | Adsorption purification, chemical regeneration |

Notes

- Combination use: In case of severe pollution, multiple methods need to be used in combination (such as centrifugal dehydration first, then vacuum dehydration).

- Oil quality testing: before and after filtration, the breakdown voltage, moisture content, dielectric loss and other indicators need to be tested.

- Safety regulations: Control the oil temperature (usually ≤65℃) during vacuum oil filtration to prevent oil oxidation.

According to the degree of pollution of transformer oil and the target standard, flexibly ｓｅｌｅｃｔ or combine the above methods.