How to separate water from transformer oil?

After water enters the transformer oil, it is necessary to effectively separate the water through physical separation, vacuum treatment, or adsorption purification to restore the insulation performance of the oil. The following are specific treatment steps and technical solutions:

Determine the degree of water ingress

1. Preliminary detection:

- Visual inspection: The oil is turbid or there is a free water layer (water accumulation at the bottom).

- Quick test: ｄｒｏｐ the oil on a hot steel plate (about 150℃). If a "crackling" sound is made, it indicates water.

2. Laboratory analysis:

- Water content (Karl Fischer method, target ≤15ppm).

- Dielectric strength (GB/T 507, target ≥60kV/2.5mm).

Separation method and operation process

1. Sedimentation separation (free water)

- Applicable conditions: a large amount of free water (such as visible stratification in the oil).

- Steps:

1. Turn off the transformer and let it stand for 24-48 hours to allow the water to naturally settle to the bottom.

2. Slowly drain the water through the oil drain valve at the bottom of the transformer (repeat several times).

- Note: Only free water can be removed; dissolved water or emulsified water cannot be treated.

Centrifugal separation

- Equipment: high-speed centrifuge (such as a disc centrifuge).

- Principle: Use the density difference between oil and water (oil 0.89-0.92g/cm³, water 1.0g/cm³) to separate under centrifugal force.

- Effect: Free water and part of the emulsified water can be treated, but dissolved water cannot be removed.

Vacuum dehydration and degassing (core method)

- Equipment: vacuum oil filter (with heating function).

- Steps:

1. Heat the oil: to 50-70℃ (reduce viscosity and promote water evaporation).

2. High vacuum treatment: vacuum degree ≤50Pa (absolute pressure), water boiling point drops below 30℃, and evaporates quickly.

3. Atomization/thin film evaporation: increase oil surface area and improve dehydration efficiency.

4. Condensation capture: evaporated water vapor is collected by the condenser and the dry oil is refluxed.

- Effect:

- Water content can be reduced to below 10 ppm.

- Synchronously remove dissolved gases (such as oxygen).

Coagulation dehydration (emulsified water treatment)

- Equipment: coalescing filter + separation tank.

- Principle:

1. Oil passes through the coalescing filter element, and tiny water droplets merge into large water droplets.

2. Large water droplets settle to the bottom of the separation tank due to gravity and are discharged.

- Applicable: oil-in-water emulsion (water content <1000ppm).

Adsorption dehydration (deep drying)

- Adsorbent: molecular sieve (type 3A), silica gel, activated alumina.

- Method:

- Offline treatment: Oil circulates through an adsorption tower (such as a molecular sieve tank).

- Online treatment: A thermosyphon adsorber (such as a silica gel respirator) is installed on the transformer.

- Effect: The moisture content can be reduced to below 5 ppm, which is suitable for trace moisture residue.

Combined process (when water ingress is serious)

1. First stage: Sedimentation or centrifugation to remove free water.

2. Second stage: Vacuum dehydration and degassing to treat dissolved water.

3. Third stage: Deep drying of adsorbent (optional).

Precautions

1. Safe operation:

- When heating, the oil temperature is ≤80℃ to prevent oil oxidation or flash explosion (the flash point of mineral oil is usually ≥140℃).

- The vacuum system needs to prevent oil spraying, and it is recommended to be equipped with an oil mist separator.

2. Oil quality detection:

- After dehydration, the dielectric strength, moisture content and acid value need to be retested.

- If the oil is severely oxidized (acid value > 0.5mg KOH/g), oil change or chemical regeneration is required.

3. Equipment maintenance:

- Regularly ｒｅｐｌａｃｅ filter elements, adsorbents, and clean centrifuge drums.

Preventive measures

1. Seal inspection: transformer oil tank, respirator (if silica gel desiccant changes color, it needs to be replaced).

2. Online monitoring: Install an oil moisture sensor (such as a capacitive or infrared probe).

3. Regular oil filtering: Especially for transformers in high humidity areas, vacuum filter the oil at least once a year.

Standard reference

- International: IEC 60422 "Guide to Maintenance of Insulating Oil".

- Domestic: DL/T 1056 "Specifications for the Management of Moisture in Transformer Oil".

The above methods can effectively separate moisture and restore transformer oil performance. If water ingress leads to an increase in solid impurities (such as sludge), mechanical filtration (1~5μm filter element) is required for further purification.