Can transformer oil still be used if there are impurities in it?

Impurities in transformer oil should never be ignored, but they don't necessarily require immediate disposal. The correct approach is to immediately remove the oil from service, conduct a professional evaluation, purify it, and only reuse it after it passes the inspection.

Why shouldn't impure oil be used directly?

The core functions of transformer oil are insulation and cooling. Any impurities will directly impair these two functions:

1. Damage insulation and cause accidents:

Water: The most dangerous impurity. Even trace amounts of dissolved water can dramatically reduce the oil's dielectric strength (breakdown voltage). Under high electric fields, it can easily cause partial discharge or even total insulation breakdown, leading to catastrophic accidents.

Solid particles, Such as metal shavings, fibers, and dust, can form "bridges" in an electric field, creating conductive pathways that can also cause discharge and breakdown.

2. Impurities can hinder heat dissipation and cause overheating:

Impurities can hinder the oil's thermal circulation, preventing heat from dissipating quickly within the transformer, resulting in localized overheating. Overheating, in turn, accelerates the vicious cycle of insulation paper degradation and aging.

3. Corrosion and Degradation:

Moisture and contaminants accelerate oil oxidation, generating acidic substances and sludge. Acids corrode metal parts and insulation, while sludge clogs oil passages, further exacerbating heat dissipation issues.

How to Handle and Decision-Making?

Visual judgment is not acceptable; scientific "oil degradation test" data is essential. This is the only criterion for determining oil reusability.

The process is as follows:

1. Step 1: Sampling and Testing

Collect oil samples from the sampling port at the bottom of the transformer and send them to a professional laboratory for analysis.

Key Indicators to be Tested:

Breakdown Voltage: This directly reflects the baseline of insulation performance.

Moisture Content: This is measured in ppm and has extremely strict requirements.

Dielectric Dissipation Factor: This is a very sensitive indicator that reflects the overall degree of oil degradation.

Chromatographic Analysis: This detects dissolved fault-signaling gases (such as hydrogen and acetylene) in the oil to determine whether there are any potential internal faults.

2. Step 2: Decision Based on the Results

Case A: Indicators meet or slightly exceed standards

Response: Use a vacuum oil filter for purification. It effectively removes moisture, gas, and solid particles.

Final requirement: The purified oil must be retested and can only be re-injected after all indicators meet standards.

Case B: Indicators significantly exceed standards (such as extremely low breakdown voltage, high acid value, and high dielectric loss factor).

This indicates that the oil is not only physically contaminated but also chemically degraded (aging).

Response: Simple filtration is ineffective and requires more complex "regeneration" treatment (such as clay adsorption) or direct replacement of the transformer oil.

Case C: Chromatographic analysis shows excessive levels of fault gases

This is often a sign of an internal transformer fault (such as discharge or overheating) rather than a problem with the oil itself.

Response: The primary priority is to troubleshoot the transformer itself, rather than treating the oil first. After troubleshooting, the oil condition can be used to determine whether to purify or ｒｅｐｌａｃｅ the oil.

Summary and Emphasis

In short, the essential process is: detect an abnormality → shut down and take a sample → test and analyze → decide whether to purify or ｒｅｐｌａｃｅ the oil based on the data → treat and retest → reuse if qualified. Any decision that skips testing is a high-risk one.