Transformer Oil Purifier

Transformer oil purifiers are essential equipment for ensuring the service life of insulation systems, as the life expectancy of a transformer is primarily determined by the useful life of its insulation system. The most widely used insulation system in transformers consists of liquid insulation (transformer oil) and solid insulation. Liquid insulation provides approximately 80% of the electrical strength of a transformer, and the majority of transformer failures — about 85% — stem from damage to the insulation system.

Transformer oil provides effective insulation and enhances the breakdown voltage of the materials it insulates. Its low viscosity allows it to penetrate solid insulation and transfer heat to the cooling system. In this regard, liquid insulation also serves as a coolant, while the resistance of transformer oil to oxidation allows it to operate at high temperatures, thus protecting the insulation system from significant damage over time.

Causes of Transformer Oil Contamination

Transformer oil contamination occurs primarily due to the wear and aging of a transformer. Over time, insulating oil deteriorates through oxidation, a process exacerbated by the presence of oxygen and moisture even under ideal conditions. This degradation is further influenced by contaminants arising from the solid components of the transformer that dissolve into the oil.

Oxidation is a chemical reaction involving unstable hydrocarbons, oxygen, and catalysts such as moisture, with heat acting as an accelerator. This process results in the breakdown of oil and the formation of acids that damage paper insulation and metallic components. The acids produce metal soaps, aldehydes, and alcohols, which eventually form sludge deposits. These deposits accumulate on insulation, cooling systems, and other components, impeding the transformer’s operation by:

• increasing oil viscosity and reducing cooling efficiency;

• accelerating the transformer aging process due to heat retention;

• causing insulation shrinkage and degradation of varnishes and cellulose materials, which absorb moisture and increase the risk of electrical discharges.

Moisture also greatly contributes to oil contamination. Water enters the oil in various forms: free, dissolved, and chemically bound within paper insulation. While the total removal of moisture from insulation is impossible, excessive moisture can reduce the dielectric strength of the oil and cause uneven distribution within the transformer. This imbalance increases the risk of breakdowns in high-stress areas.

Furthermore, contaminants smaller than 5 microns contribute significantly to oil degradation. These electrically charged and dipolar particles form sticky deposits on transformer surfaces, leading to:

• reduced heat transfer efficiency;

• increased risk of arc discharges;

• accelerated aging of cellulose insulation.

Classification of Impurities in Transformer Oils

There are three primary types of contaminants in transformer oil:

Solid particles, including microscopic debris such as metal fragments, dust, and residues from the aging of insulation materials. These contaminants usually originate from the mechanical degradation of transformer components. Particles smaller than 5 microns are particularly problematic, as they constitute approximately 80% of all impurities found in transformer oil after a few years of operation. Their small size allows them to settle on critical components, such as transformer windings, and form insulating layers that impair heat dissipation. This may result in overheating, increased oil viscosity, and accelerated aging of the solid insulation.

Water contamination. Water can enter the oil in the form of dissolved moisture or emulsified droplets. High temperatures within the transformer cause the oil to absorb more water, but when the temperature decreases, this water precipitates, forming emulsions or settling as free water. In addition, water reacts with other degradation products, forming acids and sludge that compromise the insulating properties of the oil and promote corrosion of transformer components.

Gases such as hydrogen, methane, and carbon oxides are by-products of the chemical degradation of oil under thermal stress. These gases accumulate in the oil, decreasing its dielectric strength and increasing the risk of internal discharges or arcing. The presence of such gases also serves as an indicator of potential failures, including transformer hot spots or insulation breakdown.

Methods for Purifying Transformer Oils

Purification of transformer oil is a multi-stage process intended to remove impurities and restore the original properties of the oil. The most common methods include:

Filtration focuses on removing solid particles. This is achieved with the use of fine-mesh or porous filters, which capture particulate impurities as the oil passes through. Filtration methods are classified into surface and depth filtration. Surface filters are made from materials such as woven wire mesh, paper, or cloth, and they capture particles larger than the filter’s pore size. Depth filters, on the other hand, utilize materials such as ceramics, felt, or metallic fibers, allowing them to retain impurities within their internal structure. While filtration is highly effective at removing visible solid contaminants, it does not address dissolved gases or water.

Dehydration involves removing moisture from the oil. Moisture removal is critical because water significantly reduces the dielectric strength of the oil. Dehydration is typically achieved through vacuum treatment, where the oil is exposed to a vacuum chamber. Under reduced pressure, water molecules vaporize at lower temperatures, allowing them to be extracted without affecting the composition of the oil. This process not only removes free and dissolved water but also minimizes the risk of emulsified moisture that forms during temperature fluctuations.

Finally, Degassing targets the removal of dissolved and entrained gases, such as hydrogen, methane, and oxygen. This process is also performed under vacuum conditions, which force the gases to separate from the oil. Degassing not only improves the insulating properties of the oil but also helps prevent issues such as arcing and partial discharges within the transformer.

In cases where significant chemical degradation has occurred, oil regeneration can be applied. This process involves passing the oil through adsorbents such as Fuller’s Earth or silica gel, which remove acidic compounds, sludge, and oxidation products.

FLD 30D  Fluidex Transformer Oil Purifier

The Fluidex Transformer Oil Purifier unit FLD 30D is designed to remove dissolved gases, free and dissolved water, and solid particles from transformer oil through a two-stage vacuum system. The two-stage vacuum system ensures efficient removal of contaminants and moisture from the oil. The oil is heated to reduce viscosity, making it easier to remove impurities and improve filtration efficiency. Equipped with both coarse and fine filters, the transformer oil purifier eliminates solid particles and contaminants. Additionally, the vacuum degassing and dehydration process removes dissolved gases and moisture.

Common contaminants such as moisture, gases, and solid particles can severely impact the insulation system, resulting in various faults and even complete transformer failure. In order to prevent such issues, deep purification is required, which involves the use of a transformer oil purifier that performs filtration, dehydration, and degassing. Incorporating this equipment into routine maintenance allows companies to achieve stable and predictable transformer performance.