Purification method of transformer insulating oil

The purification methods of transformer insulating oil mainly include physical purification, chemical treatment and combined processes, the purpose of which is to remove moisture, gas, particulate matter, oxides and other soluble impurities, and restore the insulation performance and chemical stability of the oil. The following are specific methods and operation points:

Physical purification method

1. Vacuum dehydration and degassing

Principle:

Under 50~65℃ and high vacuum (≤50 Pa) conditions, moisture and gas evaporate and separate.

Equipment: vacuum oil filter.

Effect:

Water content is reduced to ≤5 ppm (ultra-high voltage transformer requires ≤3 ppm).

Gas content ≤0.1%, breakdown voltage ≥60 kV.

2. Mechanical filtration (particle removal)

Principle: Intercept solid particles through filter element (1~10 μm).

Equipment: pressure oil filter, centrifugal oil filter.

Effect:

Cleanliness reaches NAS Class 6 (ISO 4406 15/12/9).

Suitable for pretreatment of oil products after maintenance.

3. Coalescence separation (emulsified water treatment)

Principle: The coalescence filter element merges tiny water droplets into large water droplets, and then separates them by gravity or vacuum.

Equipment: Coalescence dehydration oil filter.

Effect: It can treat emulsified oil with water content ≤100 ppm, and ≤10 ppm after dehydration.

Chemical treatment method

1. Adsorption purification

Principle: Use activated alumina, silica gel or molecular sieve to adsorb acids, oxides and colloids.

Method:

Percolation method: The oil is circulated through the adsorbent column.

Direct addition: Add the adsorbent to the oil and stir it before filtering (time control is required).

Effect:

The acid value is reduced to ≤0.01 mg KOH/g.

The color and dielectric loss (tanδ) are significantly improved.

2. Regeneration (waste oil recovery)

Principle: Combined clay adsorption + sulfuric acid treatment + distillation to remove deep oxidation products.

Applicable: Severely aged oil (acid value> 0.5 mg KOH/g).

Note: Professional regeneration equipment is required, and antioxidants need to be added after treatment.

Precautions

Temperature control: The oil temperature is ≤ 65℃ throughout the process to avoid oxidation.

Prevent secondary pollution:

Pipelines and storage tanks need to be clean (NAS Class 6 or below).

Use dry nitrogen to seal the oil.

Additive supplement: After purification, the antioxidant content (such as DBPC) needs to be tested and supplemented if necessary.

Safe operation:

Prevent oil spraying or oil return during vacuum oil filtration.

The adsorbent needs to be properly handled after use (hazardous waste).