Transformer Oil Processing

Operation and lifespan of oil-filled transformers heavily depend on transformer oil processing. The quality of transformer oil directly impacts the performance of power transformers, as approximately 85% of transformer failures are attributed to insulation damage. 

Impact of Impurities on Transformer Oil

One of the primary factors affecting transformer oil performance is the presence of mechanical impurities. These non-soluble substances, either suspended in the oil or settled as sediment, include fibers, dust, and degradation products from transformer materials such as varnishes and paints. Over time, impurities may also form as a result of internal transformer damage, such as overheating or electrical arcing, producing carbonized particles. These contaminants can significantly deteriorate the dielectric properties of transformer oil.

During transformer oil aging, sludge accumulates and settles on the transformer insulation, further deteriorating its performance. This sludge can reduce the dielectric strength of the oil and lower its thermal conductivity, accelerating insulation degradation. Furthermore, conductive bridges formed by sediment particles may lead to electrical failures, increasing the risk of transformer failure.

Sources of Mechanical Impurities

Mechanical impurities in transformer oil originate from various sources, including:

• Initial Filling: particles already present in the oil at the time of transformer assembly.
• Manufacturing and Assembly: impurities originating from transformer components, such as paints and varnishes.
• Operation and Aging: decomposition products such as sludge and carbon particles formed due to operational stresses and oxidation processes.

Each category of contaminants poses unique challenges to transformer performance. For instance, carbon particles formed during electrical arcing exhibit high conductivity, while sludge deposits on the windings hinder cooling and accelerate insulation degradation.

Aging and Contaminants

During operation, colloidal particles in transformer oil gradually grow in size, forming sediment over time. Studies indicate that the most dangerous particles are those smaller than 5 microns, accounting for about 95% of all contaminants. These fine particles originate primarily from oil oxidation and serve as nuclei for the formation of larger particles.

The phenomenon of "flocculation" further complicates transformer maintenance. As particles cluster together, the number of particles larger than 50 microns can increase dramatically, affecting oil properties and transformer functionality. Fine contaminants may also penetrate into solid insulation materials, altering their dielectric properties.

Categories of Deposits in Transformer Oil

Impurities in transformer oil can be classified into three primary types:

• Asphaltene Deposits: dark brown powder resulting from the oxidation of naphthenic resins. These deposits impair cooling efficiency when they settle on transformer windings.
• Soap Deposits: light to dark brown residues formed by metal–acid reactions. In the presence of moisture, these deposits may cause internal short circuits.
• Carbon Deposits: black particles formed by electrical arcs in the oil. High-voltage arcs produce fine carbon dust, while low-voltage arcs generate coarse flakes.

Metals and Fibers

Metals such as copper and aluminum used in transformer design also affect oil quality. Research has shown that copper significantly accelerates oil oxidation, while other metals such as aluminum and steel have a lesser effect. Furthermore, cellulose fibers of insulation materials adversely affect the dielectric strength of the oil, particularly in moist environments.

Methods for transformer oil processing

Transformer oil processing helps the oil maintain its insulating properties and ensures the safe operation of electrical equipment. Different methods of transformer oil purification are employed, including physical, physicochemical, and chemical methods.

1. Physical Methods of Oil Purification

Physical methods are primarily used to remove suspended dirt, dissolved gases, excess water, and resinous or coke-like impurities. The most accessible physical method is sedimentation, which involves the separation of solid impurities and water. However, this method is time-consuming and is mainly effective for particles larger than 50–100 microns. It does not efficiently remove fine particles or dissolved gases.

2. Physicochemical Methods of Oil Purification

These methods are based on physical and chemical interactions to improve oil quality. The main physicochemical methods include:

• Coagulation: this method involves the aggregation of fine particles or impurities into larger clumps, which can then be removed more easily.
• Adsorption: impurities are attracted and retained on the surface of a material, such as activated carbon, which effectively removes dissolved gases and other contaminants.
• Selective Method: this approach targets specific impurities based on their chemical properties and selectively removes them from the oil.
• Ion-exchange Method: this method involves exchanging undesirable ions in the oil with more suitable ions, improving the performance and purity of the oil.

3. Chemical Methods of Oil Purification

Chemical methods rely on chemical reactions between contaminants and chemical agents to break down or neutralize impurities. After the chemical reaction, the resulting compounds are easily removed through filtration or specialized treatment techniques such as sulfuric acid treatment, hydro-cleaning, or alkaline treatment. These methods are effective in removing both organic and inorganic contaminants, ensuring that the oil complies with the required purity standards for safe transformer operation.

FLD D Thermal Vacuum Transformer Oil Processing System

The FLD 30D unit is designed for removal of mechanical impurities, degassing, vacuum dehydration, and preparation of oils for storage, transportation, and pressurized filling into various equipment. It is suitable for treating transformer oil and other insulating oils, as well as for vacuum processing in external systems.

The system components include:

• Heater: for heating of oil before processing.
• Vacuum Chamber: for dehydration and degassing of oil.
• Vacuum Pump: creates vacuum and expels gases.
• Coarse and Fine Filters: remove mechanical impurities.
• Safety Container: protects the vacuum pump from oil ingress and includes a level sensor.
• Control Panel: for system monitoring and operation.

Routine transformer oil processing, including oil dehydration, is essential for maintaining its insulating properties and ensuring the reliable and safe operation of electrical equipment. This process helps reduce maintenance and repair costs while preventing potential failures.