Transformer Oil Dehydration: Removing Emulsified Moisture

How to Remove Emulsified Water from Transformer Oil?

Emulsified water is difficult to remove because tiny water droplets are stably dispersed in the oil. The key is demulsification, which breaks the emulsion so water can separate and be removed.

1. Vacuum Oil Filter (Best and Standard Method)

The most effective solution for transformer oil.

How it works:

Heating (45–65°C): Lowers viscosity and weakens the emulsion.

High vacuum (<100 Pa): Water boils at low temperature and evaporates.

Large surface exposure: Oil spreads into thin film for faster dehydration.

Filtration: Removes solids and sludge.

Benefits:

Deep removal of free water, emulsified water, dissolved moisture, and gases, restoring breakdown voltage and insulation performance.

2. Centrifugal Separation

Uses high-speed rotation to separate water based on density.

Best for:

Oil with high water content or as pretreatment before vacuum dehydration.

Limit:

Not effective for very stable emulsions alone.

3. Coalescing Filters

Hydrophilic elements capture small droplets and merge them into larger ones for settling.

Good for: Online moisture control.

Limit: Elements clog easily with heavy emulsions.

4. Adsorption Drying

Uses silica gel, molecular sieves, or activated alumina.

Best for: Achieving very low moisture levels after main dehydration.

Not suitable: For heavily contaminated or large oil volumes due to cost.

Methods NOT Recommended

Chemical demulsifiers — unsafe for transformer oil because they can damage electrical and chemical properties.

Standard Treatment Process

Pretreatment (optional): Centrifuge or coalescer for heavy water contamination.

Main treatment: Vacuum oil filter for deep dehydration and degassing.

Polishing: Adsorption dryer for ultra-low moisture levels (<10 ppm).

Prevention Tips

Keep transformer sealing intact.

Maintain breather desiccant.

Use nitrogen/diaphragm seals.

Monitor moisture online.

Follow correct oil-handling procedures.