Transformer oil filtration and types of transformer oil - HERING VPT
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Transformer oil filtration and types of transformer oil

types of transformer oil

Transformer oil filtration and types of transformer oil

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Transformer oil filtration is a process through which sludge, dissolved moisture, and gasses are removed to secure the oil’s quality and performance. Transformer oil is susceptible to degradation as time advances since it is exposed to acid, dust, and moisture.

What are the types of transformer oil?

Transformer insulating oil may be paraffin-based or naphtha based. Paraffin-based oil is obtained from crude containing n-paraffin which is less oxidized than naphtha-based paraffin. Naphtha-based oil, on the other hand, contains less amount of n-paraffin.


Ascertaining contamination in transformer oil

In the process of deterioration, transformer oil darkens with an increase in acid content. As pertaining to the chemical properties, the moisture content is measured as parts per million or ppm through the Coulometric Karl Fischer Titrator. The acidity test is derived as mg of KOH needed to neutralize the acid in a gram of oil. Focusing on the physical properties of transformer oil, the interfacial tension between oil and water molecules, flash point or the temperature at which oil gives vapors to make the flammable mixture, pour point (the minimum temperature at which oil starts to flow) and viscosity are observed to study contamination in the oil.


Classifying transformer oil treatment

Transformer oil treatment plants are classified based on filtration systems, treatment methods include filtration, purification and regeneration which is also known as reclamation. Based on end use, transformer oil is treated in different methods for utility, method and other requirements.


Why is transformer oil filtration needed?

Filtration and maintenance is important for transformer oil since it not only enhances performance but also ensure safety and ease of operation for the transformer maintenance team. Transformer oil is also known as insulating oil owing its name to excellent insulating attributes and stability at high temperatures. It stops arcing and corona discharge besides reducing heat of the transformer and thereby acting as a coolant. The transformer oil protects the core and winding of the apparatus and prevents oxidation of the cellulose paper insulation.


Why should the transformer be free from moisture?

The presence of moisture reduces the dielectric strength of the transformer oil and affects the insulation resistance of the oil. It also reduces the density and lubricating properties of the oil. The absence of moisture in transformer oil is an essential parameter because it minimizes the aging rate of the oil and enhances the safe operation and reliability of the transformer.


Factors that determine the quality of transformer oil

Entities including breakdown voltage, moisture content, neutralization value, interfacial tension, color, test for oxidation stability, flash point, pour point, viscosity, sludge test and dissolved gas analysis (DGA) helps in ascertaining qualities of insulating oil. The temperature of transformer oil increases as the load increases and results in expansion of oil volume which in turn pushes air outside the tank. When the load decreases oil volume decreases resulting in vacuum formation in the top part of the transformer oil tank.

Such vacuum encourages exterior air to enter the transformer tank which brings moisture and dust along with it. At this point, silica gel comes to the rescue of the transformer and dries down air to a dew point below minus 40 degrees celsius and employs an oil seal cup to remove dust particles.


Role of breather in transformer oil filtration

Silica gel or breather uses its hygroscopic nature and absorbs moisture from the air and prevents moisture from entering the oil tank while breathing. It is a pot of silica gel through which air passes when the transformer breathes. The previously used blue silicon gel is no longer in vogue as the cobalt chloride that it contains is declared a human toxin and is banned in European countries. The blue silica gel is replaced by orange silica gel which in turn contains silicon dioxide and is in beaded form. These dry beads absorb moisture and become green in colour when saturated with moisture.


Transformer oil filtration method

The temperature increases to more than 65 degrees celsius, whose latent heat separates moisture and gasses. This classifies oil viscosity and facilitates the separation process. Following this, sludge and dirt are removed by employing filter candles either as edge filter or depth filters. Filter cartridges and edge-type paper filters are also used for the purpose.

Dirt is also separated from the oil by a centrifugation method which in turn saves money since it does not require the replacement of filters. The oil is finally subjected to the degassing chamber where gas is removed and oil is fit to assist the effective functioning of transformers. High-quality oil that results due to transformer oil filtration increases life span of the transformer, decreases transformer failure and enhances return on investment thus adding to the profits.

Hering transformer oil filtration: Unparalleled pioneer in the industry

Prone to increasing and recurrent exposure to increasing voltages and stresses, transformer insulating oils require compatible treatment solutions that complement the transformer’s infrastructure. Incepted in 1909 and backed by more than century-old expertise, Hering offers a spectrum of solutions for transformer maintenance of which the EOK transformer oil purification product line is one.

Hering EOK series ensures that the transformer’s insulating fluids function in optimal operating points, thereby asserting high performance of the apparatus. Supported by German engineering, Hering offers the EOK series which is a benchmark in oil purification and degasification technology that removes most volatile acids.

Hering offers purification plants in three series namely EOK Basic, Standard, and Professional lines which remove sludge materials and are tailored to specific requirements. The filtering systems are popular for their robust design, simple operation and easy maintenance. Other products include oil regeneration systems, PCB removal systems, transformer drying ovens, waste oil recycling plants, reactivation clay polishing systems, adsorbent mineral polishing systems and TIDO series online transformer insulation drying and degassing systems and ISODRY series online transformer insulation drying systems.

Hering offers onsite service for plants including those older than 30 years and are available for assistance round the clock throughout the year. They also offer onsite training on customer requests. They also insist on quality awareness among its staff which reflects in unbeatable international quality standards.










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