How to effectively purify transformer oil?

Transformer oil purification is a key step to ensure the safe operation of power equipment. It mainly removes moisture, gas, particulate matter and oxides in the oil to restore its insulation strength, cooling performance and chemical stability. The purification treatment method of this system is as follows:

The core method of transformer oil purification

1. Vacuum dehydration and degassing (key process)

- Equipment: vacuum oil filter (including heating system, vacuum pump, atomization device)

- Process flow:

1. Heating: oil temperature is controlled at 60-65℃ (avoid exceeding 70℃ to avoid accelerated oxidation)

2. Atomization: Atomize the oil into the vacuum tank to form a thin film and increase the evaporation area

3. Vacuuming: the vacuum degree is maintained at ≤133Pa (1mmHg), and the boiling point of water is reduced to about 20℃

4. Condensation: evaporated water and gas are extracted by the vacuum pump, condensed and collected

- Effect:

- Water content: ≤10ppm (new oil standard)

- Gas content: ≤0.1% (volume ratio)

Precision filtration

- Filter element grade: β₅≥200 (NAS) 1638 5th level, particle size ≤3μm)

- Special requirements:

- Use glass fiber filter material (oil-resistant, acid-resistant and alkali-resistant)

- Configure the magnetic filter to absorb iron chips

Adsorption purification (optional)

- Applicable working conditions: when acid value > 0.05mgKOH/g or dielectric loss factor (tanδ) exceeds the standard

- Method:

- Silica gel/activated alumina: remove polar compounds (processing capacity is about 3-5% of oil weight)

- Molecular sieve: selectively adsorbs trace moisture (can reduce moisture to below 5 ppm)

Standardized treatment process

1. Pretreatment

- Sampling and testing: Determine moisture (ASTM D1533), breakdown voltage (IEC 60156), acid value (ASTM D664)

- Coarse filtration: remove visible impurities through a 20μm filter

2. Main treatment stage

- Circulation purification: The oil passes through the vacuum oil filter at a flow rate of 2000-3000L/h and circulates 3-5 times

- Online monitoring: Real-time detection of breakdown voltage (target ≥ 60kV/2.5mm) and water content

3. Post-treatment

- Standing degassing: Standing for 24 hours after purification to release residual microbubbles

- Supplementary additives: Add antioxidants (such as T501, concentration 0.3%)

Special working condition treatment plan

| Problem | Solution |

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

| Severe emulsification | First centrifugal separation (3000rpm, 15min) to break the emulsion, then vacuum dehydration |

| High gas content | Adopt membrane degassing technology (40% higher efficiency than traditional vacuum) |

| Metal particle contamination | Adopt electrostatic oil purifier (can remove 0.1μm particles) |

| Deep oxidation | White clay adsorption (add 2-3% activated white clay, stir at 80℃ for 2 hours) + precision filtration |

Key control parameters

| Indicator | New oil standard | Requirements after purification | Test method |

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

| Breakdown voltage | ≥60kV | ≥55kV | IEC 60156 |

| Moisture content | ≤10ppm | ≤15ppm | ASTM D1533 |

| Acid value | ≤0.01mgKOH/g | ≤0.03mgKOH/g | ASTM D664 |

| Dissipation factor (90℃) | ≤0.005 | ≤0.01 | IEC 60247 |

Precautions

1. Safety regulations:

- The vacuum system must be explosion-proof (oil vapor ignition point ≥140℃)

- Open flames are strictly prohibited at the processing site, and carbon dioxide fire extinguishers are equipped

2. Oil temperature control:

- The surface temperature of the heater is ≤80℃ to avoid local overheating and cracking

3. Environmental protection requirements:

- Waste oil and adsorbents are treated as HW08 hazardous wastes

Application of advanced technologies

- Online oil purification system: integrated sensors for real-time monitoring, automatic start and stop purification (such as ABB Oil PuriQ)

- Low temperature vacuum technology: 40℃ low temperature dehydration to reduce the risk of thermal aging

- Nanocellulose adsorption: new materials can remove moisture and acidic substances at the same time (experimental stage)

Through the method, transformer oil can be restored to a performance close to that of new oil, extending its service life to more than 15 years (IEC 60422 standard). For ultra-high voltage transformers above 500kV, it is recommended to test the above once a year, and the oil quality below 220kV is tested every 3 years.