How to clean up turbid transformer oil?

Impurities in transformer oil (such as metal particles, fibers, dust, carbides, etc.) will reduce the insulation performance of the oil and accelerate the aging of equipment, so they must be handled in time. The following are the treatment methods and operating steps:

Determine the type of impurities and the degree of contamination

1. Visual inspection

- Take an oil sample to observe the color (normally light yellow and transparent). If it is black, turbid, or has suspended matter, it means that impurities are present.

2. Laboratory testing

- Particle counting: Detect the particle size and number of impurities (such as NAS 1638 or ISO 4406 standards).

- Breakdown voltage: Impurities will cause the breakdown voltage to decrease (the standard requires ≥40kV).

Treatment methods

Choose one or a combination of the following solutions according to the type of impurities and the degree of contamination:

1. Mechanical filtration (applicable to solid particles)

- Equipment: plate oil filter, centrifugal oil filter.

- Steps:

1. ｓｅｌｅｃｔ a filter element with appropriate precision (such as 1~5μm).

2. Circulate and filter the transformer oil until the particulate matter meets the standard (the filter element can be judged by the pressure difference of the oil filter machine, whether it is blocked).

- Note:

- Before filtering, the oil needs to be left to stand to allow large particles to settle.

- When it is seriously polluted, the filter element needs to be replaced several times.

2. Vacuum oil filtration (comprehensive treatment of water + impurities)

- Equipment: vacuum oil filter (with multi-stage filtration).

- Steps:

1. Heat the oil temperature to 50~60℃ (reduce viscosity and improve filtration efficiency).

2. Turn on vacuum dehydration and precision filtration (filter element accuracy ≤3μm).

3. Circulate the treatment until the oil sample is clear and the water content is ≤ 10 ppm.

Adsorption treatment (for tiny colloidal impurities)

- Materials: silica gel, activated alumina, or molecular sieve.

- Method:

- Load the adsorbent into the bypass circulation system of the oil filter machine to adsorb colloidal impurities.

- Or add the adsorbent directly to the oil (need to be filtered and removed later).

Electrostatic oil purification (ultrafine particle treatment)

- Principle: Use an electrostatic field to absorb tiny particles of 0.01~1μm.

- Applicable: Ultra-high voltage transformers with extremely high requirements for oil cleanliness.

5. Oil change (when seriously polluted)

- If there are too many impurities in the oil (such as severe carbonization or excessive metal content), it is necessary to completely ｒｅｐｌａｃｅ the oil and flush the inside of the transformer.

Operation precautions

1. Safety protection

- Wear protective gloves and glasses during operation to avoid oil contact with skin.

- Stay away from fire to prevent oil vapor from burning.

2. Prevent secondary pollution

- All pipes and valves must be flushed with new oil before use.

- Keep the transformer sealed during oil filtering to prevent air from entering.

3. Filter element replacement

- ｒｅｐｌａｃｅ the filter element immediately when the pressure difference exceeds 0.3MPa.

Post-treatment verification

1. Sampling test

- Particle size: by ISO 4406 standard (such as 15/12/9).

- Dielectric loss (tanδ): ≤0.5% (at 90℃).

- Breakdown voltage: ≥50kV (new oil standard ≥60kV).

2. Transformer test

- After filtering the oil, let it stand for 24 hours, and perform a withstand voltage test and a partial discharge test.

Preventive measures

- Regular maintenance: Check the oil quality at least once a year, and the transformer in a harsh operating environment needs to be shortened the cycle.

- Sealing protection: Add silica gel desiccant to the transformer respirator to prevent moisture and dust from entering.

- Online monitoring: Install a particle sensor in the oil to monitor the impurity content in real time.