The power transformer oil treatment procedure is a critical process for maintaining the insulating properties and performance of transformer oil. Transformer oil, over time, can degrade due to contamination by moisture, gases, and particulate matter, which can compromise the efficiency and safety of the transformer. The treatment procedure helps to remove these contaminants and restore the oil’s properties.
Step-by-Step Power Transformer Oil Treatment Procedure
1. Initial Inspection and Oil Testing
- Visual Inspection: Check the appearance of the oil for signs of discoloration, cloudiness, or the presence of sediment. Discoloration could indicate oxidation or contamination.
- Oil Sampling: Take oil samples to perform laboratory tests. These tests typically include:
- Moisture Content: The presence of water reduces the dielectric strength of the oil.
- Acidity: High acidity indicates oil degradation, often due to oxidation.
- Dissolved Gas Analysis (DGA): Identifies gases like hydrogen, methane, carbon monoxide, which can indicate transformer faults.
- Dielectric Strength: Measures the insulating capacity of the oil.
- Particle Count: Assesses solid contaminants in the oil.
2. Preliminary Oil Dehydration (Moisture Removal)
- Vacuum Dehydration: The oil is exposed to a high vacuum in a transformer oil purifier. This reduces the pressure inside the system, causing water (which has a lower boiling point at reduced pressures) to evaporate and be removed.
- Heating: In some cases, the oil is gently heated to aid the dehydration process without affecting the oil’s quality.
- Moisture Collection: The moisture evaporated from the oil is condensed in a separate chamber, ensuring the oil is kept dry.
- Target Moisture Level: The final moisture content should be less than 10 ppm (parts per million) for optimal transformer operation.
3. Filtration (Solid Particulate Removal)
- Initial Filtration: The oil passes through a series of filters designed to remove large particulate matter, dirt, and sludge. This could include mesh filters, fine filters, or cellulose-based filter materials.
- Deep Bed Filtration: For more thorough purification, activated clay or silica gel-based filters are often used to remove finer solid contaminants and improve the oil’s cleanliness.
- Sludge Removal: Some oils may contain sludge, which is a product of oxidation. The use of chemical adsorbents or specific filtration methods can effectively remove these contaminants.
4. Degasification (Gas Removal)
- Vacuum Degasification: As oil can dissolve gases such as nitrogen, oxygen, and carbon dioxide, these gases are removed using vacuum treatment. The vacuum lowers the boiling point of these gases, causing them to escape.
- Gas Stripping: In some cases, the system may employ a gas-stripping process to enhance the degasification.
- Dissolved Gas Monitoring: After treatment, ensure that the oil is free from harmful dissolved gases. The level of dissolved gases should be minimized to improve the oil’s insulating properties.
5. Oil Regeneration (Optional)
- Chemical Treatment: If the oil shows signs of severe degradation (e.g., high acidity, oxidation), chemical treatment may be required. This process uses regenerative adsorbents such as activated clay or silica gel to neutralize acids and remove oxidation products.
- Color and Odor Removal: This treatment also helps restore the oil’s color and remove any unpleasant odors caused by oxidation.
- Filtering with Regenerative Materials: Regenerative filtration can further refine the oil, removing remaining contaminants and rejuvenating its insulating properties.
6. Blending (If Needed)
- If the oil has significantly deteriorated or is mixed with contaminants beyond recovery, blending with fresh oil may be necessary. The new oil must meet the same specifications as the original oil.
- Blending Ratio: Carefully calculate the proper ratio of fresh oil to used oil to achieve optimal performance.
7. Final Filtration and Polishing
- Polishing Filters: The oil is passed through finer filters or polishing stages to ensure that no particulate matter, including microscopic dust and fibers, remains.
- Final Purification: This ensures the oil is free from solid, liquid, and gas contaminants, achieving the highest quality before returning the oil to the transformer.
8. Dielectric Strength Testing
- After treatment, measure the dielectric strength of the oil to confirm it meets the required standards (usually 30 kV for 1mm, or higher depending on transformer specifications).
- Further Treatment: If the dielectric strength is still below the acceptable level, additional treatment (e.g., re-vacuuming, further degasification, or filtration) may be needed.
9. Oil Recharging
- Transformer Oil Filling: Once the oil is purified and treated, it is pumped back into the transformer. The filling process should be done under vacuum to avoid any air ingress, which could cause oxidation of the oil.
- Oil Level Check: Ensure the oil level is correct according to the transformer specifications. If necessary, top off with fresh oil.
10. Post-Treatment Inspection
- Final Gas Analysis: Perform a final gas analysis to ensure that no harmful gases remain in the oil.
- Electrical Tests: Conduct electrical tests to check the performance of the transformer with the newly treated oil.
- Leak Check: Verify that there are no oil leaks around the transformer seals or components.
Conclusion
The transformer oil treatment procedure is designed to restore the oil’s insulating properties by removing moisture, gases, and solid contaminants. The process includes vacuum dehydration, filtration, degasification, and optional oil regeneration. It’s a crucial step in maintaining transformer health, enhancing performance, and preventing failures due to poor oil quality. Proper oil treatment not only improves transformer reliability but also extends its operational life, reducing the risk of unplanned downtime and costly repairs.
