Transformer oil dewatering method

Dehydration of transformer oil is an important part of maintaining the insulation performance of transformers. The presence of water will accelerate oil aging and reduce insulation strength. The following are common methods and precautions for dehydrating transformer oil:

Physical method

(1) Vacuum dehydration (vacuum oil filtration)

- Principle: Under vacuum conditions, the boiling point of water decreases (e.g., the boiling point is ≈5°C at a vacuum of about 1kPa at 50°C), and the water evaporates and is pumped out by the vacuum pump.

- Equipment: vacuum oil filter (including heating, vacuum, and filtration systems).

- Steps:

- Heat the oil to 50~60°C (avoid excessively high temperatures that may cause oil oxidation).

Oil is atomized or forms a thin film in the vacuum tank, increasing the area for water evaporation.

- Maintain a high vacuum (usually <1kPa) for several hours until the water content reaches the standard (e.g., ≤10ppm).

- Advantages: Efficient removal of free and dissolved water, suitable for large-scale processing.

(2) Centrifugal separation

- Principle: Use centrifugal force to separate free water with a higher density from the oil.

- Applicable scenarios: preliminary treatment of high moisture content (such as free water precipitation).

- Disadvantages: Unable to remove dissolved water, needs to cooperate with other methods.

Adsorption method

(1) Molecular sieve/silica gel adsorption

- Materials: Use 3Å molecular sieve, activated alumina, or dry silica gel (need to be activated and regenerated).

- Method:

- Pressure oil filter: The oil flows through the adsorbent filter bed.

- Direct addition: Add the adsorbent to the oil and stir it before filtering (to prevent dust residue).

- Note: The adsorbent needs to be replaced or regenerated regularly to avoid reverse release of water after saturation.

(2) Cellulose filter paper filtration

- When filtering oil, absorbent filter paper is used, which can absorb some water, but the efficiency is low and is suitable for auxiliary treatment.

Thermal cycle drying

- Method: Circulate the oil through the heater (70~80℃) and condenser, and the water evaporates and condenses in the condenser.

- Applicable scenarios: Transformer body with oil drying (such as when slightly damp).

Chemical method (auxiliary means)

- Use water-absorbing additives, such as silicon-based compounds, but it may affect the oil quality and need to be carefully evaluated.

- Note: Chemical methods may introduce by-products and require subsequent filtration.

Key notes

1. Safe operation:

- Prevent oil spraying or oil return during vacuum oil filtration.

- The heating temperature does not exceed 65°C to avoid oil oxidation.

2. Moisture detection:

- Use Karl Fischer method or dielectric loss meter to detect moisture content before and after treatment (target: ≤10~15ppm).

3. System sealing:

- Ensure the transformer is sealed after treatment (such as replacing the respirator silicone) to prevent air moisture backflow.

4. Comprehensive treatment:

- Severely emulsified oil needs to be demulsified first (such as centrifugation), and then combined with vacuum and adsorption.

Selection basis

- Water content slightly exceeds the standard (≤30ppm): vacuum oil filtration + adsorption.

- Large amounts of free water: first centrifugal separation, then deep dehydration.

- Online treatment: install a continuous vacuum dehydration device or an adsorption oil filter.

Timely water removal can significantly extend the life of the transformer. It is recommended to regularly monitor the moisture content and breakdown voltage in the oil (≥50kV/2.5mm is qualified).