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Time：2025-05-26 13:47:10 Reading volume：
The main purpose of transformer oil degassing is to remove dissolved gases (such as oxygen, nitrogen, hydrogen, etc.) and trace moisture in the oil to restore or improve the insulation performance of the oil, delay the aging of the oil, and ensure the safe operation of the equipment. The specific purposes and technical details are as follows:
1. Improve insulation strength (breakdown voltage)
- Dissolved gases (especially oxygen) will reduce the dielectric strength of the oil. After degassing, the breakdown voltage can be restored from ≤30kV to ≥60kV (GB/T 507 standard), avoiding local discharge or arc breakdown.
2. Prevent oxidative degradation of the oil
- Oxygen reacts with oil molecules to produce aging products such as organic acids and colloids. After degassing, the service life of the oil is extended (new oil acid value ≤0.01mg KOH/g, operating oil acid value ≤0.1mg KOH/g).
3. Eliminate the risk of bubbles
- When the temperature or pressure changes, the dissolved gas in the oil may precipitate to form bubbles, resulting in local insulation weakness or discharge (for example, when the transformer load changes suddenly).
4. Reduce equipment corrosion
- The combined effect of oxygen and moisture will accelerate the rusting of metal parts (such as core and winding), and degassing can protect the internal structure of the transformer.
5. Meet the strict requirements of high-voltage equipment
- Ultra-high voltage (≥500kV) transformers have extremely strict requirements on the gas content in oil (for example, oxygen ≤300ppm, moisture ≤5ppm), and deep degassing is required.
1. Before new oil injection
- New oil may dissolve in the air during transportation and storage, and degassing treatment is required to meet qualified indicators.
2. After transformer maintenance
- During overhaul, the oil is exposed to the air, the gas content increases, and reprocessing is required.
3. Maintenance of oil in operation
- When regular inspections find that the gas exceeds the standard (for example, the total gas content ≥3% by volume), degassing treatment is required.
4. Regeneration of faulty oil
- The performance of damp or slightly oxidized oil can be restored through degassing, dehydration and filtration.
| Parameters | Control requirements | Test methods |
|------------------|-------------------------------------|---------------------|
| Total gas content | ≤0.5%~1% (volume ratio) | DL/T 423 (vacuum pressure difference method) |
| Oxygen content | ≤300ppm (ultra-high pressure ≤100ppm) | ASTM D3612 |
| Moisture content | ≤10ppm (processed simultaneously with degassing) | IEC 60814 |
| Breakdown voltage | ≥60kV/2.5mm (after degassing) | IEC 60156 |
1. Temperature control: heat to 50~60℃ (too high will accelerate oxidation).
2. Vacuum degree: keep above -0.095MPa (absolute pressure ≤5kPa).
3. Cycle time: usually 4~8 hours, depending on the initial gas content.
4. Safety protection: The vacuum system needs to be designed with an anti-return oil device to avoid pump damage.
- Case 1: The oxygen content in the oil of a 220kV transformer was too high (2000ppm). After 3 years of operation, the acid value rose to 0.15mg KOH/g, causing winding corrosion.
- Case 2: The non-degassing oil precipitated bubbles at low temperatures, causing partial discharge and eventually breaking through the bushing insulation.
Transformer oil degassing is not only a "purification" process, but also a key link in preventive maintenance, especially for high-voltage and large-capacity transformers. Combined with vacuum dehydration and fine filtration, the performance of the oil can be fully restored and unplanned downtime can be reduced.
