The power transformer oil filtration procedure is a vital maintenance process aimed at improving the performance, insulating properties, and longevity of the transformer. Transformer oil is essential for both insulation and cooling of the transformer. Over time, the oil can become contaminated with moisture, gases, acidity, sludge, and particulate matter, which can reduce its efficiency and cause equipment failure if not addressed.
Here is a detailed breakdown of the power transformer oil filtration procedure:
1. Preparation and Initial Inspection
1.1. Prepare the Equipment
- Oil Filtration Unit: ｓｅｌｅｃｔ an appropriate oil filtration unit, such as a vacuum oil purifier, pressure filtration unit, or high-efficiency filtration rig.
- Check Oil Level: Ensure that the transformer oil level is at the proper level, and that there are no significant leaks or low oil conditions.
- Gather Sampling Equipment: Prepare tools for collecting oil samples (bottles, gloves, etc.).
1.2. Sample and Analyze the Oil
- Visual Inspection: Inspect the color and clarity of the oil. Dark or cloudy oil indicates contamination.
- Test Moisture Content: Measure moisture in the oil. The moisture level should be less than 20 parts per million (ppm) for optimal performance.
- Measure Dielectric Strength: Test the oil’s dielectric strength, which indicates its insulating ability.
- Check for Acidity: Perform a Total Acid Number (TAN) test. Elevated acidity can indicate oil degradation.
- Gas Analysis: Check for dissolved gases using a gas chromatograph or DGA (dissolved gas analysis) to determine if there are any abnormal gas levels indicating internal issues like overheating or arcing.
2. Isolation and Preparation of the Transformer
Before starting the filtration process, ensure that the transformer is de-energized and properly isolated.
2.1. Disconnect the Transformer
- De-energize the Transformer: Shut off the transformer from the electrical grid to ensure no electrical current is flowing.
- Isolate Transformer: Ensure that the transformer is electrically isolated and safe to handle.
2.2. Ensure Safety Precautions
- Safety Gear: Wear appropriate Personal Protective Equipment (PPE), such as gloves, safety glasses, and protective clothing.
- Proper Ventilation: Ensure that the area is well-ventilated, especially if using equipment that generates heat or gases.
3. Filtration Process
The filtration process typically involves the use of vacuum filtration, high-efficiency filters, or a combination of both. The main goal is to remove contaminants like moisture, gas, and particulate matter.
3.1. Vacuum Oil Filtration
- Vacuum Dehydration: The oil is heated slightly (around 40-60°C) and then passed through a vacuum chamber. The vacuum lowers the pressure, causing any water (moisture) in the oil to evaporate at a lower temperature.
- Moisture Removal: The evaporated water is removed by condensation in a moisture separator or coalescing filter. Coalescing filters can help aggregate small water droplets into larger ones, making them easier to remove.
- Degassing: A degassing section removes dissolved gases (e.g., hydrogen, methane) from the oil to improve its insulating properties.
- Filtration: The oil is then passed through fine mesh filters or depth filters to remove particulate matter (dirt, sludge, and oxidation by-products).
- Fine Filtration: After the main filtration, the oil is often passed through a high-efficiency filter to remove fine contaminants, ensuring the oil is as pure as possible.
3.2. Additional Filtration (if necessary)
- Activated Carbon Filtration: If the oil has high acidity or contains dissolved gases, activated carbon filters are used to absorb these contaminants.
- Coalescing Filters: If the oil is emulsified with water (i.e., water is dispersed in fine droplets within the oil), coalescing filters help combine these droplets into larger droplets, which are then removed.
- High-Efficiency Particulate Filters: To remove fine solid contaminants (such as metallic particles), high-efficiency particulate filters (e.g., HEPA filters) may be used.
4. Monitoring and Adjusting the Filtration Process
During the filtration process, continuous monitoring is essential to ensure optimal performance.
4.1. Oil Temperature
- Maintain the oil temperature in the range of 40°C to 60°C to prevent overheating and to ensure the oil flows effectively through the filtration system.
4.2. Filtration Time
- The filtration time will depend on the volume of oil, the extent of contamination, and the type of filtration system being used. Monitor the oil quality continuously to decide when the filtration process is complete.
4.3. Pressure Monitoring
- Maintain appropriate vacuum or pressure levels in the filtration system to ensure efficient operation. Too high or too low pressure can reduce the efficiency of the filtration process.
5. Post-Filtration Analysis
After the filtration process is completed, perform tests to ensure the oil is of the correct quality before refilling it into the transformer.
5.1. Re-Test Oil Quality
- Moisture Content: Test the oil to ensure moisture levels have been reduced to acceptable levels (typically less than 20 ppm).
- Dielectric Strength: Measure the dielectric strength of the oil to ensure it meets the required standards for insulation.
- Acidity: Check the Total Acid Number (TAN) to ensure it is within acceptable limits.
- Particle Count: Perform a particle count to ensure that solid contaminants have been effectively removed.
- Gas Content: Use a gas chromatograph to ensure dissolved gases are within acceptable limits.
5.2. Oil Return
- After passing all quality checks, the cleaned oil is refilled into the transformer. Ensure the oil is added to the proper level.
6. Re-Energizing the Transformer
Once the oil filtration is complete, the transformer can be re-energized.
6.1. Check for Leaks
- Inspect all seals, gaskets, and oil filling points for leaks before starting the transformer.
6.2. Energize the Transformer
- After ensuring that everything is sealed correctly, power up the transformer and monitor its performance.
6.3. Final Monitoring
- Monitor the transformer for any abnormal sounds, oil temperature, and oil level fluctuations during the first few hours of operation. Make sure there are no signs of leaks or malfunctions.
7. Disposal of Contaminated Oil
The used, contaminated oil needs to be disposed of properly.
7.1. Waste Oil Disposal
- The contaminated oil must be disposed of or recycled according to local environmental regulations. In many cases, the oil can be sent to a recycling facility for re-refining or neutralization of contaminants.
8. Record Keeping and Documentation
Finally, it’s essential to maintain a record of the filtration process and oil quality tests for future reference.
- Oil Filtration Logs: Document the start and end times of the filtration process, as well as the oil test results.
- Transformer Maintenance Records: Include the oil filtration procedure as part of the regular maintenance schedule.
Frequency of Transformer Oil Filtration
- Transformer oil should generally be filtered every 3-5 years as part of routine maintenance, but this may vary depending on the transformer’s operating conditions (e.g., load, environment).
- Filtration may be done more frequently if the oil tests show high levels of contaminants, especially moisture or particulate matter.
- Triggered Filtration: If the transformer shows signs of overheating, loss of insulation resistance, or gas buildup, oil filtration should be done immediately.
The power transformer oil filtration procedure is crucial for maintaining the transformer’s insulating and cooling properties. The procedure involves removing contaminants such as moisture, gases, sludge, and particulates, ensuring that the transformer operates efficiently and safely. Regular monitoring and proper post-filtration analysis ensure that the oil remains within acceptable standards for maintaining optimal transformer performance and preventing failures.
