Transformer Oil Moisture Problems: Hazards and Best Dehydration Techniques

Water in Transformer Oil: Risks, Consequences, and Essential Treatment Measures

Water contamination in transformer oil is one of the most dangerous issues affecting transformer reliability, insulation performance, and operational lifespan. Even small amounts of moisture can trigger rapid degradation of both oil and solid insulation. In essence, water in transformer oil is like a hidden time bomb—and understanding its effects is crucial for safe transformer operation.

How Water Damages Transformer Oil Performance

1. Severe Reduction in Insulation Strength (Most Critical Risk)

Mechanism:

Pure transformer oil has high dielectric strength. However, water droplets (especially in the free state) have a much higher dielectric constant and will polarize under an electric field, forming conductive “bridges.”

Consequences:

Sharp decrease in breakdown voltage

Higher likelihood of partial discharge

Potential insulation failure even under normal voltage

Increased risk of catastrophic electrical accidents

2. Accelerated Oil Aging and Oxidation

Mechanism:

Moisture accelerates oxidation reactions in transformer oil, especially in the presence of heat, oxygen, and metal catalysts.

Consequences:

Increased acid value: Corrosion of metal components and insulation paper

Sludge formation: Deposition on windings, cooling ducts, and core surfaces, causing heat dissipation problems

Vicious aging cycle: More sludge → poorer cooling → faster aging

Damage to Transformer Solid Insulation (Paper and Pressboard)

Transformer solid insulation, mainly cellulose-based, is extremely sensitive to moisture.

1. Hydrolytic Aging of Cellulose

Mechanism:

Water breaks the long polymer chains of cellulose, reducing the Degree of Polymerization (DP).

Consequences:

Structural weakening of insulation paper

Increased brittleness and cracking

Risk of winding deformation during short-circuit forces

Direct reduction of transformer service life

2. Moisture Circulation Between Oil and Paper

Oil and paper constantly exchange moisture depending on temperature.

High temperature → moisture migrates from paper to oil

Low temperature → oil reabsorbs moisture into paper

This dynamic moisture cycle accelerates both oil deterioration and cellulose aging, creating a long-term degradation loop.

Additional Hazards to Transformer Components and Operation

1. Corrosion of Metal Components

Moisture combined with acidic aging byproducts corrodes:

Core clamps

Tank walls

Bolts, metal supports

Magnetic circuit components

This corrosion weakens the structural integrity and magnetic performance of the transformer.

2. Reduced Heat Dissipation and Overheating

Moisture lowers oil’s thermal conductivity

Sludge blocks cooling channels

The transformer running temperature rises significantly

Excessive temperature further accelerates insulation aging, forming a continuous deterioration cycle.

Forms of Moisture in Transformer Oil and Their Harm Levels

Knowing the form of moisture is key to choosing the right dehydration method:

1. Dissolved Water

Water is fully dissolved in oil

Minimal impact on breakdown voltage

Still accelerates oxidation and cellulose hydrolysis

2. Emulsified Water

Water dispersed as tiny droplets

Oil turns cloudy or milky

Significant ｄｒｏｐ in dielectric strength

3. Free Water (Most Dangerous)

Visible water droplets settling at the tank bottom or suspended in oil

Quickly forms conductive paths

Highest risk of insulation breakdown

Summary: Why Water in Transformer Oil Is Dangerous

Moisture contamination leads to:

Lower insulation strength

Faster oil oxidation and sludge formation

Accelerated aging of insulating paper

Corrosion of transformer metal parts

Impaired cooling and overheating

Increased risk of partial discharge and breakdown

Left untreated, water can directly cause transformer failure, explosions, or fires.

How to Remove and Prevent Water in Transformer Oil

1. Regular Oil Testing

Monitor key parameters such as:

Water content (ppm)

Breakdown voltage

Acid number

Interfacial tension (IFT)

Dissolved gas analysis (DGA)

2. Online Moisture Monitoring

Install real-time moisture sensors for early detection of water ingress.

3. Effective Dehydration Methods

For light to moderate moisture:

Vacuum oil purifier with heating and vacuum dehydration

Hot oil circulation to remove dissolved, emulsified, and free water

For severe moisture contamination:

Transformer shutdown for vacuum hot oil spray drying

Insulation drying or factory repair if moisture penetrates solid insulation

4. Preventing Moisture Intrusion

Ensure proper sealing of gaskets, breathers, and conservator systems

ｒｅｐｌａｃｅ silica gel regularly

Minimize exposure to air during installation and maintenance

Inspect for leaks and breathing system failures