How can we separate transformer oil and water?

Separating the water from transformer oil is a key step in maintaining the insulation performance of the transformer. The following are commonly used physical separation and chemical treatment methods. You can choose the appropriate method according to the actual situation:

Physical separation method

(1) Sedimentation method (gravity separation)

- Principle: The density of water and oil is different (water density ≈ 1g/cm³, transformer oil ≈ 0.8-0.9g/cm³). After standing, the water will settle to the bottom.

- Operation steps:

1. Put the contaminated transformer oil into a sedimentation tank or transformer oil tank.

2. Let it stand for 24-48 hours to allow the water to settle naturally.

3. Drain the water from the bottom drain valve.

- Applicable situations: The water content is high (such as free water), but emulsified water or trace water cannot be removed.

(2) Centrifugal separation method

- Principle: Use the centrifugal force generated by the high-speed rotation of the centrifuge to accelerate the separation of oil and water.

- Operation steps:

1. Pump the oil into a centrifuge (such as a disc centrifuge).

2. Adjust the speed (usually 5000-10000 rpm) so that the water is thrown to the outer wall and discharged.

3. Collect the purified oil.

- Advantages: fast speed, suitable for large-scale processing.

- Disadvantages: high equipment cost and requires regular maintenance.

(3) Vacuum dehydration method (most effective)

- Principle: Heat the oil (60-70℃) in a vacuum environment (<50mbar) to evaporate the water and pump it away.

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

- Operation steps:

1. The oil is heated to 50-70℃ (to avoid excessive temperature causing oil oxidation).

2. The oil enters the vacuum tank, the water evaporates and is pumped out by the vacuum pump.

3. The dried oil is finely filtered (1-5μm) to remove residual particles.

- Advantages: It can remove trace water (down to below 10ppm) and restore the insulation properties of the oil.

- Applicable cases: Applicable to emulsified water or dissolved water (when the sedimentation method cannot separate).

(4) Coalescing separation method

- Principle: Use a coalescing filter element to merge tiny water droplets into large droplets, and then discharge them through the separation layer.

- Equipment: Coalescing oil filter.

- Applicable cases: Applicable to emulsified water in oil (water droplets <1μm).

Chemical adsorption method (auxiliary means)

(1) Molecular sieve adsorption

- Principle: Use 3Å molecular sieve (zeolite) to adsorb trace water in oil.

- Operation: Place the molecular sieve in the oil or in the oil filter adsorption tank for circulation filtration.

- Advantages: It can reduce the water content to below 5ppm, suitable for high precision requirements.

(2) Silica gel or activated alumina

- Putting desiccants (such as silica gel) into the oil to absorb moisture, but the efficiency is low and it is suitable for small-scale treatment.

Preventing moisture from entering again

- Keep the transformer sealed: Check the breather (whether the silica gel desiccant is ineffective).

- Regular oil testing: Monitor the moisture content (GB/T 7600 or ASTM D1533).

- Control the oil temperature: Avoid condensation caused by drastic temperature changes.

Choose the right method

|            Method               |                     Applicable situations                         |         Dehydration effect          |                        Remarks                            |

|---------------------------|-------------------------------------------------------|---------------------------------|----------------------------------------------|

| Sedimentation method | Free water (large amount)                                      | General (remaining 100ppm) | Simple but inefficient                               |

| Centrifugation method | Free water, a small amount of emulsified water     | Better (remaining 50ppm)      | Requires professional equipment            |

| Vacuum dehydration     | Emulsified water, dissolved water (trace amount)  | Excellent (<10ppm)                | Most commonly used, suitable for transformer maintenance |

| Coagulation method     | Emulsified water (tiny water droplets)                    | Better (remaining 30ppm)      | Need to cooperate with other methods |

| Molecular sieve             | Ultra-low moisture requirement (<5ppm) | Best    | High cost                                |

Recommended process:

1. Sedimentation first (remove most of the free water) →

2. Vacuum dehydration (thorough drying) →

3. Molecular sieve adsorption (ultra-high purity requirement).

If the water is seriously emulsified, it can be pre-treated with a centrifuge or coalescing oil filter, and then vacuum dehydrated.

If conditions permit, it is recommended to use an online oil filter to continuously maintain the quality of transformer oil.