Why should transformer insulating oil be filtered?

Transformer insulating oil filtration is important to maintain transformer performance and safety. The main reasons include the following aspects:

1. Remove moisture and moisture

Hazard: Moisture reduces the dielectric strength (breakdown voltage) of insulating oil, resulting in an increased risk of partial discharge or short circuit while accelerating the aging of oil and solid insulating materials (such as cardboard).

- Filtration: Remove moisture through vacuum oil filtration or adsorbents (such as silica gel) to restore the insulating properties of oil.

2. Remove solid impurities

- Source: Metal particles, fibers, dust, or aging and shedding of insulating materials generated during operation.

- Hazard: Impurities may form conductive paths, causing partial discharge or short circuit; they may also wear internal parts of the equipment (such as tap changers).

- Filtration method: Use mechanical filtration (such as filter element, centrifugal separation) to remove particulate matter.

3. Eliminate dissolved gases

- Fault gas: Transformer faults (such as overheating, arcing) will produce gases such as hydrogen, methane, acetylene, etc., which are dissolved in the oil.

- Hazards: Gases reduce the insulation properties of the oil and are a sign of internal faults (detectable by oil chromatography).

- Treatment: Vacuum degassing or nitrogen replacement to restore the chemical stability of the oil.

4. Delaying oil aging

- Oxidation products: The reaction of oil with oxygen will produce oxidation products such as acids and sludge.

- Hazards: Acidic substances corrode metal parts, and sludge blocks oil channels and affects heat dissipation.

- Solution: Filter to remove oxidation products and add antioxidants when necessary.

5. Restore physical and chemical indicators

- The parameters of the filtered oil (such as dielectric strength, acid value, dielectric loss factor) must meet the standards (such as IEC 60296 or GB/T 7595) to ensure that it:

- The insulation performance meets the standards.

- Good heat dissipation capacity.

- Non-corrosive.

6. Preventive maintenance

- Regular filtration can extend the service life of the oil, reduce the frequency of transformer shutdown and maintenance, and reduce operating costs.

Filtration time

- Before new oil is injected (may contain transport or storage contaminants).

- Routine maintenance (such as when oil test indicators exceed the standard).

- After transformer overhaul (to prevent installation impurities from entering).

- Post-fault processing (such as internal discharge or overheating).

Common filtration technology

- Vacuum oil filter: efficient dehydration and degassing.

- Pressure oil filter: remove solid particles.

- Adsorption purification: Use silica gel or activated alumina to remove acidic substances.

Through filtration, insulating oil can continue to play the role of insulation, cooling and arc extinguishing, ensuring the safe and stable operation of the transformer.