Transformer oil purification is a crucial process that helps restore the quality of transformer oil by removing contaminants, including moisture, gases, solid particles, and oxidation byproducts. This ensures the oil maintains its insulating and cooling properties, prolonging the lifespan of transformers and preventing failures.
Here are the primary methods of transformer oil purification:
1. Vacuum Dehydration
- Objective: To remove moisture (water) from transformer oil, which is one of the most damaging contaminants for transformer insulation.
- Process:
- The oil is heated to a specific temperature (typically 50°C–70°C) and then placed under a vacuum.
- The low pressure inside the vacuum chamber lowers the boiling point of water, causing moisture to evaporate at lower temperatures.
- The moisture is then extracted through condensation or collected using a moisture separator.
- Advantages:
- Very effective at removing water and dissolved gases.
- Helps restore the dielectric strength of the oil.
- Applications: Ideal for oils with high moisture content.
2. Vacuum Degassing
- Objective: To remove dissolved gases (such as hydrogen, carbon dioxide, nitrogen, and oxygen) from transformer oil, which can degrade the oil’s insulating properties.
- Process:
- The oil is placed under vacuum in a degassing chamber.
- Gases dissolved in the oil are released due to the reduced pressure and are separated from the oil.
- The released gases are then safely vented out of the system.
- Advantages:
- Removes harmful dissolved gases that can cause insulation breakdown.
- Helps restore the oil’s dielectric strength and prevents transformer failure.
- Applications: Used in situations where the oil has absorbed gases, often due to high-temperature operation or electrical discharges.
3. Filtration (Solid Particulate Removal)
- Objective: To remove solid contaminants such as dust, dirt, sludge, and particles suspended in transformer oil.
- Process:
- The oil is passed through a series of coarse and fine filters that trap solid particles.
- Common filtration methods include cellulose filters, fiberglass filters, or synthetic filters, which vary in mesh size depending on the required level of filtration.
- Vacuum filtration systems can be used to assist with removing particles from the oil.
- Advantages:
- Efficient in removing large and small particles.
- Prevents clogging of transformer components and reduces the risk of electrical arcing.
- Applications: Typically used for oils with high levels of suspended solids.
4. Clay Treatment (Oil Regeneration)
- Objective: To regenerate aged oil, especially oils that have become acidic or have degraded due to prolonged use.
- Process:
- Activated clay or fuller's earth is added to the oil to absorb oxidation products, acidic compounds, and other harmful byproducts.
- The oil is passed through the clay, which adsorbs impurities, thereby purifying the oil.
- The treated oil is then separated from the clay.
- Thermal treatment may be applied in conjunction with clay to enhance the regeneration process.
- Advantages:
- Restores the oil’s chemical properties, improving its dielectric strength.
- Reduces the acidity of the oil and removes oxidation products.
- Applications: Used for regenerating oil that has high acidity, oxidation products, or other degradation signs.
5. Centrifugal Filtration
- Objective: To separate solid particles and water from transformer oil using centrifugal force.
- Process:
- The oil is spun at high speeds in a centrifugal separator.
- Due to the differences in density, water (being heavier) and solid contaminants are forced toward the outer edges of the rotor, while the purified oil remains in the center.
- The separated water and solids are drained off, and the clean oil is collected for reuse.
- Advantages:
- Rapid separation of solid and water contaminants from oil.
- Can handle large quantities of oil at once.
- Applications: Suitable for high-capacity applications or when a fast separation of particles and water is needed.
6. Activated Carbon Treatment (Oil Polishing)
- Objective: To remove fine impurities, oxidation products, and residual chemicals from transformer oil.
- Process:
- The oil is passed through a bed of activated carbon, which adsorbs impurities such as dissolved gases, acids, and organic contaminants.
- The activated carbon traps these contaminants, polishing the oil and improving its dielectric strength and chemical stability.
- Advantages:
- Provides high-efficiency removal of organic contaminants.
- Can be used as a final step after other purification methods to achieve higher purity.
- Applications: Used for polishing oil that has been treated by other methods but still contains residual impurities.
7. High-Efficiency Filtration (Fine Polishing)
- Objective: To achieve a very high level of purity by removing ultra-fine particles (down to microns or sub-microns).
- Process:
- The oil is passed through high-precision filter media (e.g., cellulose, fiberglass, or synthetic fibers) that can capture very fine particles.
- These filters often have a very fine mesh or multiple stages of filtration to remove the finest particles.
- Advantages:
- Effective in achieving extremely clean oil with minimal particulate contamination.
- Enhances the life and performance of transformers.
- Applications: Suitable for final-stage purification, especially when oil cleanliness is critical.
8. Oil Regeneration (Chemical Treatment)
- Objective: To restore the chemical balance and properties of transformer oil that has degraded over time.
- Process:
- In addition to clay treatment, other methods include chemical regeneration using special additives that neutralize acids, restore the oil’s dielectric strength, and reduce oxidation.
- Regeneration may involve the use of chemical reagents that interact with impurities to neutralize them or break them down into non-harmful compounds.
- Advantages:
- Restores the chemical properties of the oil and neutralizes acids.
- Reduces the need for oil replacement and prolongs the life of both the oil and the transformer.
- Applications: Typically used for heavily degraded oil that needs to be restored to usable conditions.
9. Thermal Treatment
- Objective: To remove gases and contaminants through heating.
- Process:
- Transformer oil is heated to a certain temperature, often combined with vacuum or high-speed flow systems, to help break down contaminants such as gases and water.
- The oil is typically heated to around 50°C–70°C to help release moisture, gas, and some light oxidation products.
- Advantages:
- Effective for removing gases and moisture.
- Can be combined with other methods like vacuum dehydration or vacuum degassing.
- Applications: Typically used in combination with other purification processes.
10. Coalescing Filtration
- Objective: To efficiently remove free water and other contaminants by aggregating small water droplets into larger droplets for easier removal.
- Process:
- Coalescing filters capture and merge tiny water droplets into larger drops, which are easier to separate from the oil.
- This process can be used alongside other filtration methods for enhanced water removal.
- Advantages:
- Effective for removing free water from transformer oil.
- Reduces the water content to safe levels.
- Applications: Used in systems where there is a significant amount of free water in the oil.
Conclusion
The methods of transformer oil purification vary depending on the contaminants present in the oil and the specific requirements for restoring the oil’s insulating properties. Most purification systems employ a combination of techniques (vacuum dehydration, filtration, degassing, and regeneration) to achieve the best results. These methods help maintain the efficiency, safety, and longevity of transformers by ensuring the oil remains free from moisture, particles, and gases that could degrade its performance.
