Purification system for filtering transformer oil

The purification system for filtering transformer oil is mainly used to remove moisture, gas, particulate matter and degradation products in the oil to restore its insulation performance and chemical stability and ensure the safe operation of the transformer. The following are the key technologies and system design points for transformer oil purification:

Main pollutants in transformer oil

- Moisture: free water, dissolved water (reduces dielectric strength and accelerates oil aging).

- Gas: dissolved air (O₂, N₂) or fault gas (H₂, CH₄, C₂H₂, etc.).

- Solid particles: metal chips, fibers, carbon particles (trigger partial discharge).

- Oxidation products: acids, sludge (reduce insulation performance).

Core technologies of the purification system

(1) Vacuum dehydration and degassing

- Principle: Heat the oil in a vacuum tank (usually 60~70℃) and evaporate moisture and gas through negative pressure.

- Key equipment:

- Vacuum pump: maintain high vacuum (≤0.1 mbar). - Atomization device: Increase the surface area of the oil (such as spray or film evaporation).

- Effect: Water content can be reduced to ≤10 ppm, gas content ≤0.1%.

(2) Precision filtration

- Filter element grade: 1~5 microns (remove particulate matter, ISO cleanliness can reach ≤14/12 level).

- Multi-layer filtration:

- Pre-coarse filter (10~25 microns) protects the main filter element.

- Post-adsorption filter element (such as activated carbon) removes acidic substances.

(3) Adsorption purification

- Materials:

- Molecular sieve: Selectively adsorbs water and polar compounds.

- Silica gel/activated alumina: Removes acid value and sludge.

- Application method:

- Online circulation: Oil flows through the adsorption tower.

- Offline processing: Batch purification (suitable for severely deteriorated oil).

(4) Electrostatic oil purification (optional)

- Applicable scenarios: ultrafine particles (0.01~1 micron) or colloidal pollutants.

- Note: Vacuum dehydration is required to avoid the risk of electrostatic breakdown.

(5) Deacidification (chemical regeneration)

- Method:

- Alkaline earth adsorbent (such as white clay) neutralizes acidic substances.

- Ion exchange resin: deep deacidification (for high acid value oil).

Typical purification system process

1. Pretreatment: coarse filtration (25 microns) to remove large particles.

2. Heating: oil temperature rises to 50~70℃ (reduces viscosity and improves dehydration efficiency).

3. Vacuum dehydration and degassing: remove moisture and dissolved gases in a vacuum tank.

4. Precision filtration: A 1~5 5-micron filter element intercepts particles.

5. Adsorption purification (optional): through a molecular sieve or silica gel tower.

6. Post-treatment: cool to ambient temperature and inject back into the transformer after passing the test.

Maintenance and precautions

- Real-time monitoring: online detection of moisture (ppm), dielectric strength (kV), acid value (mg KOH/g).

- Filter element replacement: Replacement is required when the pressure difference exceeds 0.3 MPa.

- Safety measures:

- Explosion-proof design of vacuum system (avoid accumulation of combustible gas).

- Strict control of heating temperature (≤70℃).

- Environmental protection requirements: waste oil and adsorbents need to be professionally recycled.

Transformer oil purification needs to combine vacuum dehydration, precision filtration, adsorption regeneration and other technologies, and ｓｅｌｅｃｔ a combination solution according to the degree of oil deterioration. For UHV transformers or high-humidity environments, it is recommended to configure a fully automatic online purification system to achieve continuous maintenance. The specific design needs to refer to oil product testing data (such as the IEC 60422 standard).