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Time：2025-07-24 14:59:45 Reading volume：
Filtering transformer oil is a crucial measure to maintain power equipment, extend the service life of oil products, and ensure the safe operation of transformers. The following are several efficient and practical filtering methods, as well as key considerations:
1. Vacuum oil filtering method (most recommended)
- Principle: Heat the oil in a vacuum environment to separate water, gas and impurities, and filter solid particles through a precision filter element.
- Advantages:
- It can remove water (reduced to less than 10ppm), gas (gas content <0.1%) and particles (filtered to 1-5μm) at the same time.
- Suitable for severely deteriorated oil (such as emulsified oil).
- Equipment: Vacuum oil filter (such as domestic ZYD series or imported Pall, Hy-Pro equipment).
2. Pressure oil filtering method
- Principle: Pressurize the oil to pass through the filter paper or filter element, mainly to remove solid particles.
- Applicable scenarios:
- Lightly contaminated oil (such as a small amount of metal chips, fibers).
- Quick on-site processing (when there is no vacuum equipment).
- Note: The filter paper needs to be replaced frequently (every 8-12 hours or when the pressure difference is >0.3MPa).
3. Centrifugal separation method
- Principle: Use centrifugal force to separate impurities of different densities (such as water, metal particles).
- Advantages: Suitable for treating large amounts of oil containing free water.
- Disadvantages: Limited effect on dissolved water or tiny particles (<1μm).
4. Adsorption purification method
- Materials: silica gel, activated alumina or molecular sieve.
- Application: Deep removal of acidic substances, colloids and trace moisture (better with vacuum method).
1. Pretreatment test
- Test the breakdown voltage (GB/T 507), moisture content (ASTM D1533), acid value (IEC 62021) and particle count (NAS 1638) of the oil sample to determine the pollution level.
2. Filtration process
- Vacuum oil filtration:
- Heat the oil temperature to 50-65℃ (avoid oxidation above 70℃).
- Maintain the vacuum degree <-0.095MPa, and filter in a cycle until the index is qualified (usually 3-5 times).
- Pressure filtration:
- ｓｅｌｅｃｔ a 3-5μm filter element and control the pressure at 0.1-0.4MPa.
3. Post-processing
- After filtration, let it stand for 24 hours, and re-test the withstand voltage (should be ≥50kV/2.5mm) and micro-water (≤15ppm).
1. Safety regulations
- Fire and explosion prevention: Open flames are prohibited at the oil filtration site, and the equipment is well grounded.
- Moisture-proof: Avoid open-air operations on rainy days, and suspend when the humidity is >80%.
2. Deterioration of oil quality
- If the acid value in the oil is >0.1mg KOH/g or the dielectric loss (90℃) is >4%, it is recommended to change the oil instead of filtering.
3. Equipment maintenance
- Regularly clean the oil filter storage tank and ｒｅｐｌａｃｅ the filter element (every 100 tons of oil processed or when the pressure difference alarm is triggered).
- Oil containing metal particles: add a magnetic filter (such as adding a neodymium magnet) to absorb iron filings.
- Mixed with other oils: If silicone oil or synthetic ester is mixed, fractionation technology must be used for separation.
- For small distribution transformers (<500kVA), professional oil filtering services can be outsourced.
- For large main transformers (≥220kV), it is recommended to purchase a vacuum oil filter by yourself, which has lower long-term costs.
Through standardized operation and reasonable selection, the filtering of transformer oil can restore its performance to nearly the standard of new oil (according to the IEC 60422 standard), significantly extending the replacement cycle (from 3-5 years to 8-10 years).
