How long does it take to filter transformer oil?

The filtration time of transformer oil depends on factors such as the degree of oil pollution, the performance of the filtering equipment, and the target index requirements. It usually takes 8 to 72 hours. For details, please refer to the following categories:

1. Conventional filtration (mild pollution)

- Time: 8 to 24 hours

- Applicable scenarios: The oil is slightly damp or contains a small amount of mechanical impurities (such as routine maintenance).

- Process:

- Single cycle filtration (vacuum oil filter + precision filter element).

- Sampling and testing every 4 hours until the moisture content is ≤15ppm and the breakdown voltage is ≥50kV.

2. Deep filtration (moderate pollution)

- Time: 24 to 48 hours

- Applicable scenarios: The water content in the oil is high (30 to 50ppm), the gas content exceeds the standard, or there are many particulates.

- Key operations:

- Multi-stage circulation: first, pressure filter the oil (to remove particles), then vacuum dehydration and degassing (need to be repeated 2 to 3 times).

- Heating assistance: maintain oil temperature at 60°C±5°C to improve dehydration efficiency.

3. Treatment of severely contaminated or aged oil

- Time: 48~72 hours (or even longer)

- Applicable scenarios: oil sludge deposition, excessive acid value (＞0.1mg KOH/g), or oil that has not been replaced for a long time.

- Special measures:

- Add adsorbent, such as silica gel or activated alumina (requires subsequent filtration to remove residues).

- Staged treatment: mechanical filtration first, vacuum dehydration, and finally chemical regeneration (if necessary).

4. Key factors affecting filtration time

| Factors | Impact description |

|------------------|-----------------------------------------------------------------------------|

| Initial contamination | The higher the water/particle content, the longer the time (e.g., it may take an additional 12 hours to reduce the water content from 50ppm to 10ppm). |

| Equipment performance | High-flow vacuum oil filter (e.g. 6000L/h) is more than 50% faster than small equipment (1000L/h). |

| Temperature control | When the oil temperature is 60°C, the dehydration speed is 2~3 times faster than that at 40°C, but over-temperature oxidation should be avoided. |

| Vacuum | When the vacuum degree is ≤0.5kPa, the dehydration efficiency is significantly improved (need to be combined with atomization or membrane technology). |

| Oil volume | Large transformers (e.g., 50 tons of oil) may need to be filtered in sections, extending the total time. |

5. Operation suggestions

1. Real-time monitoring: Check moisture, breakdown voltage, and dielectric loss every 2~4 hours to avoid oil aging caused by excessive filtration.

2. Number of cycles: Usually, 3~5 full oil cycles are required (tank volume ÷ oil filter flow × number of cycles).

3. Termination condition: Two consecutive test results meet the standard (e.g., moisture ≤10ppm, particle size NAS 1638 Class 6).

6. Example calculation

- Transformer oil volume: 10 tons

- Oil filter flow: 2000L/h

- Theoretical single cycle time: 10,000L ÷ 2000L/h = 5 hours

- Actual total time: If 3 cycles + test interval are required, it will take about 20~30 hours.

Notes

- Live oil filtering: If filtering while the transformer is running, the flow rate needs to be reduced (≤5% tank volume/hour) and the time is extended by 30%~50%.

- Ambient humidity: In a humid environment, the dehydration time needs to be extended or the dry air injection needs to be increased.

By properly planning equipment and processes, efficiency and oil quality recovery effects can be balanced.