How to purify transformer insulating oil？

Purifying transformer insulating oil is essential for maintaining the efficiency and longevity of transformers. Over time, insulating oil can become contaminated with moisture, gases, acids, and solid particulates, all of which can degrade the oil’s performance and lead to equipment failure. Transformer oil purification restores the oil’s insulating properties and helps prevent electrical failures or fires.

There are several methods to purify transformer insulating oil, depending on the type and level of contamination. Below are the most common purification methods:

 1. Vacuum Oil Dehydration (Vacuum Dehydration Process)

   - Purpose: Removes moisture from the oil, which is one of the most common contaminants.

   - How It Works: In this process, the oil is heated under a vacuum to lower the boiling point of water, allowing moisture to evaporate and be removed.

     - Oil Heating: The oil is heated to a temperature (usually 60-70°C) to reduce its viscosity and help in removing water.

     - Vacuum Application: The vacuum chamber helps in reducing the air pressure, which accelerates the evaporation of water at lower temperatures.

     - Water Removal: As the oil is heated and the vacuum is applied, the moisture in the oil is vaporized and extracted from the system.

 - Benefits:

     - Removes water and moisture effectively, preventing transformer failures due to dielectric breakdown.

     - Improves the dielectric strength and insulation properties of the oil.

   - Applications: Used in most transformer oil purification systems, especially for water content removal.

 2. Vacuum Oil Degassing (Vacuum Degassing Process)

   - Purpose: Removes gases (such as air, hydrogen, methane, carbon dioxide, and nitrogen) dissolved in the oil.

   - How It Works: Similar to the vacuum dehydration process, the oil is placed in a vacuum chamber where the pressure is lowered to allow dissolved gases to escape.

     - Heating: The oil is often heated during the process to aid the release of dissolved gases.

     - Vacuum Application: The vacuum reduces the solubility of gases in the oil, causing them to form bubbles and escape from the oil.

     - Gas Extraction: The gases are extracted from the oil using a separate vent system.

 - Benefits:

     - Improves the oil's dielectric strength, as dissolved gases can impair the insulating properties of the oil.

     - Prevents gas accumulation within the transformer, which could otherwise cause overheating or breakdown of insulation.

   - Applications: This process is particularly important for transformers that have been in service for long periods, as gases build up over time.

 3. Filtration (Mechanical Filtration)

   - Purpose: Removes solid contaminants such as dust, dirt, carbon particles, and sludge.

   - How It Works: Filtration can be done using various types of filter media, including diatomaceous earth filters, cotton filters, or paper filters.

     - Inline Filtration: The oil is passed through a filter to capture solid particles, which are then removed from the system.

     - Depth Filters: These filters can trap finer particles that are suspended in the oil.

   - Benefits:

     - Improves oil clarity and quality.

     - Helps prevent clogging of oil flow channels and damage to transformer components.

   - Applications: Ideal for removing particulate contamination and improving oil cleanliness.

 4. Clay Treatment (Acid-Activated Clay)

   - Purpose: Removes acidity and polar contaminants, such as oxidation products and by-products of oil degradation (e.g., acids and sludge).

   - How It Works: In this process, activated clay (usually a mixture of fuller’s earth or acid-activated bentonite clay) is mixed with the oil to absorb and neutralize acidic compounds.

     - The oil is treated with a specific amount of activated clay, which binds with acids and polar contaminants.

     - After the treatment, the oil is filtered to remove the clay along with the bound contaminants.

- Benefits:

     - Reduces the acid number and removes polar contaminants that may lead to oil degradation.

     - Helps in restoring the chemical stability of the oil.

   - Applications: Effective for aging transformer oils that have been exposed to high temperatures and have started to degrade.

 5. Centrifugal Purification

   - Purpose: Separates solid particles and water from the oil using centrifugal force.

   - How It Works: In this process, the oil is passed through a centrifuge that spins the oil at high speeds. The centrifugal force pushes heavier particles (such as solids and water) to the outer wall, where they are collected and separated.

     - The centrifugal force creates a difference in density, which facilitates the separation of water and solids from the oil.

Benefits:

Can be used for continuous oil purification.

Highly effective for removing sludge, dirt, and water from oil.

Applications: Common in on-site oil purification for transformers, especially when the oil has high levels of suspended solids.

6. Polymer Treatment (Adsorption)

Purpose: Used to remove acids and other contaminants through adsorption.

How It Works: This process involves passing the oil through a bed of adsorptive polymers that bind to acids, moisture, and other polar contaminants.

Silica gel and activated carbon are often used as adsorbents to attract and remove contaminants.

Benefits:

Effective for transformer oils with high acidity or degraded oil.

Helps restore oil quality without changing the chemical properties of the oil.

Applications: Suitable for treating aging transformer oils and restoring their dielectric strength.

7. Oil Regeneration (Vacuum and Dehydration with Filtration)

Purpose: Full purification that removes water, gases, and solid particulates while regenerating the oil’s properties.

How It Works: This combined process typically involves vacuum dehydration, degassing, filtration, and activated clay treatment to regenerate the oil.

The oil is subjected to multiple stages of purification to ensure the removal of moisture, gases, and particulates.

It may also involve adsorption or clay filtration to remove chemical degradation products (like acids).

Benefits:

Provides comprehensive purification and regeneration of oil.

Restores the dielectric strength and improves the oil’s insulation properties.

Extends the life of transformer oil.

Applications: Used for regenerating old or contaminated transformer oils and prolonging the life of transformers.

Key Considerations for Transformer Oil Purification:

Oil Type: The type of transformer oil (mineral oil, silicone oil, or synthetic ester) will influence the purification method. Some oils may be more susceptible to degradation or contamination and require different purification techniques.

Contamination Level: Assess the degree of contamination in the oil. If the oil is heavily contaminated with water, vacuum dehydration will be the most effective method. If it’s acidic or degraded, clay treatment or regeneration might be necessary.

Cost and Equipment: The complexity and cost of purification methods vary. For instance, vacuum dehydration and regeneration require more advanced equipment, while filtration and centrifugal purification are more cost-effective and simpler.

Time and Frequency: If the transformer is used in a critical application, it may require frequent oil purification or treatment. In contrast, oil regeneration may be done only during periodic maintenance.

Environmental Impact: Consider the disposal and handling of waste by-products (e.g., spent adsorbents, sludge, and degraded oil). Use environmentally friendly methods when possible, especially when using materials like activated clay.