Can used transformer oil still be used?

Whether used transformer oil can continue to be used requires a comprehensive judgment based on the oil quality test results and specific application scenarios. The following are the key evaluation steps and decision-making basis:

Core indicators for judging whether transformer oil can be reused

| Test items | Qualification standards | Risk of exceeding standards |

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

| Breakdown voltage | ≥30 kV (operating oil) | Insulation performance decreases, which may cause short circuits |

| Moisture content | ≤30 ppm (conventional)/ ≤15 ppm (ultra-high voltage) | Accelerate oil aging and reduce dielectric strength |

| Acid value | ≤0.1 mg KOH/g | Corrosion of metal parts inside equipment |

| Dielectric loss factor | ≤0.04 (at 90°C) | Increased insulation loss and heating risk |

| Particle contamination | NAS 1638 Class 8 or less | Blocking cooling channels and affecting heat dissipation |

| Dissolved gas analysis | No abnormal gas (such as sudden increase in acetylene and hydrogen) | Indication of internal discharge or overheating failure |

Reuse treatment plan (according to the degree of pollution)

1. Mild pollution (indicators are close to qualified)

- Treatment method: vacuum filtration + precision filter element dust removal.

- Effect: The insulation performance can be restored and it can continue to be used for the original equipment or a low-voltage transformer.

2. Moderate pollution (acid value/water content slightly exceeds the standard)

- Treatment method:

- Vacuum dehydration (60~65°C, vacuum degree ≤0.5 kPa).

- Adsorbent treatment (silica gel or activated alumina to remove acidic substances).

- Application scenario: non-critical equipment or short-term emergency use.

3. Severe pollution (multiple indicators exceed the standard)

- Treatment method:

- Chemical regeneration: white clay adsorption or sulfuric acid-alkali washing (professional equipment is required).

- Degraded use: as heat treatment oil or mechanical lubricant (non-power use).

- Note: If acetylene (C₂H₂) or metal particles are detected, it indicates an internal fault and the oil should be scrapped.

Non-reusable scrapping standards

When any of the following conditions occur, the oil must be replaced:

- Breakdown voltage < 20 kV (even after filtration, it still does not meet the standard).

- Acid value > 0.3 mg KOH/g (indicating severe oxidation).

- Oil sludge or carbonized particles are visible to the naked eye (physical irreversible contamination).

- Dissolved gas indicates internal faults (such as acetylene > 5 ppm).

Environmental protection and safety precautions

1. Waste oil treatment:

- Direct dumping is prohibited and must be handed over to a qualified waste oil recycling company (refer to the "National Hazardous Waste List").

- You can contact a professional company for regeneration and refining (such as distillation and purification).

2. Operational safety:

- Fire and explosion prevention during filtration (oil temperature is controlled below 70°C).

- Let the oil sample stand for 24 hours before testing to avoid bubbles interfering with the results.

Economic Suggestions

- Comparison of costs:

- The cost of filtration and regeneration is about 30%~50% of the new oil.

- If the treatment cost exceeds 70% of the new oil price, it is recommended to ｒｅｐｌａｃｅ it directly.

Conclusion: Used transformer oil can be reused after professional testing and treatment, but strict evaluation indicators and equipment requirements are required. If the pollution is serious or involves high-voltage equipment, it is safer and more reliable to ｒｅｐｌａｃｅ with new oil.