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Time：2025-07-09 13:58:08 Reading volume：
Water mixed into transformer oil will seriously affect its insulation performance and the safe operation of the equipment. Whether to continue to use it needs to be determined based on the water content and oil quality. The following is a detailed analysis:
- Degradation of insulation performance: Water will significantly reduce the dielectric strength (breakdown voltage) of the oil and increase the risk of short circuit.
- Accelerated oxidation: Water and impurities in the oil form acidic substances that corrode the iron core, windings and insulating paper.
- Partial discharge: Water vaporizes under the action of the electric field, causing bubble discharge and damaging solid insulating materials.
- Low temperature freezing: In cold environments, water freezing may cause oil channel blockage or mechanical stress damage.
- New transformer oil: Water content should be ≤20ppm (IEC 60422 standard).
- Oil in operation (different voltage levels have different requirements):
- ≤110kV: ≤35ppm
- 220kV: ≤25ppm
- 500kV and above: ≤15ppm
- Dielectric strength requirements:
- New oil breakdown voltage ≥40kV/2.5mm (GB 2536)
- Oil in operation ≥30kV/2.5mm (regular testing is required).
Detection method
- Karl Fischer titration: The laboratory accurately determines ppm-level moisture.
- Dielectric strength tester: quickly judge insulation performance (breakdown voltage drops significantly when moisture is high).
- Infrared spectroscopy: detects dissolved water and free water in oil.
Treatment measures
- Slight moisture (close to the upper limit):
- Use a vacuum oil filter to dehydrate (temperature 60-70℃ + vacuum degree <50Pa).
- Add adsorbent (such as silica gel or molecular sieve), but it needs to be replaced regularly.
- Severe contamination (emulsification or excessive water content):
- ｒｅｐｌａｃｅ new oil and dry the transformer at the same time (hot oil circulation or hot air drying).
- Check whether the seals, breathers (silica gel needs to be replaced if it changes color) and condensation points are valid.
- Mineral transformer oil (such as 25, 45): easy to absorb water, water needs to be strictly controlled.
- Synthetic ester oil: slightly higher water absorption, but can degrade water, suitable for high humidity environments.
- Silicone oil: good hydrophobicity, but high cost, mostly used in special occasions.
1. Shutdown inspection: If online monitoring finds that the water content exceeds the standard or the breakdown voltage drops, it should be shut down immediately.
2. Dehydration treatment:
- Vacuum filter the oil until the water content meets the standard (500kV equipment is recommended to be <10ppm).
- Test the gas in the oil before and after treatment (to prevent water and arc from producing hydrogen).
3. Drying of solid insulation: If the insulation paper contains water (which can be judged by the furfural content in the oil), it needs to be dried offline.
- Sealing system: Check the sealing of capsule oil storage cabinets or metal expanders.
- Breathing device maintenance: The silica gel should remain blue (turn pink when it fails), and an electric heating breathing device can be installed in humid areas.
- Regular monitoring:
- Micro-water test at least once a year (once every six months in humid areas).
- Online monitoring of moisture in oil (such as a fiber optic sensor).
Conclusion
- Unusable: If the breakdown voltage is <30kV or the water content exceeds the standard by 1.5 times, the oil must be replaced and repaired.
- Emergency treatment: If the water content exceeds the standard slightly, the oil can be vacuum filtered, but it needs to be retested and confirmed within 48 hours.
Note: Transformer oil water treatment needs to be carried out by professionals to avoid blind heating (which may cause oil cracking) or random mixing of oil (additives of different brands may react).
