With 60 years of experience and patented solutions, Transorfilter Sweden design and manufacture transformer filters for degassing and filtration of transformer oil.

Transformer oil filtration system, TF-series

Degassing principle with an even flow of oil over specially developed degassing plates in different sizes or special Raschig rings. With this process, a controlled and highly efficient degassing is obtained.

Patented filtration technology with own produced lamella filter elements for particle filtration of transformer oil. The filter rods have a long service life as they can be cleaned by built-in backflush function using compressed air. Alternatively, solutions with filter cartridges are also available in the newer systems. However, these are not back-flushable.

The new TF series is available in various standard models with a flow capacity of 500 – 12000 L/h. Most common is TF 6000 L/h as this model has adjustable flow. These are also available in several selectable designs and can be adapted according to customer specification.

TF On Load for energized power transformers

Automatic On Load filter for oil treatment of live, operating, energized transformers. Process sensor-controlled system with automatic valves for continuous safety process control.

RCID On Load cellulose insulation dry-out system

With RCID On load cellulose insulation dry-out system, drying of the transformer cellulose insulation is carried out. This is done by filtering transformer oil and drying through columns of granulated synthetic adsorbents. No heating of oil is required which makes this an energy efficient process.

This product is used as service equipment or as a fixed installation on transformers for continuous monitoring / reconditioning of the transformer cellulose insulation and transformer oil.

Power transformer lifetime

Power transformer lifetime is determined by lifetime of its cellulose insulation. Moisture content in transformer has a major influence on solid insulation aging rate and on network stress resistance. According to the world leader insulation material manufacturers, increase of water content in cellulose for 1% doubles the rate of its aging.

Degree of polymerization (DP) is defined as value of the average chain length of cellulose molecule. New cellulose has DP value of ca 1200, while end of cellulose lifetime is reached when DP value decreases to about 200. Once cellulose is degraded to unacceptable level it is considered that power transformer should be replaced. The majority of transformers breakdowns are attributed to the failure of the insulating system.

Oil-cellulose insulating system maintenance is crucial for the power transformer lifetime.

Water in power transformers

Water in power transformers occurs from three sources:

  • Water left from production
  • Athmosphere water (unmainteained breathers and gaskets)
  • Chemically created water by cellulose depolimerization


Special is our standard. Transformer oil filters are often designed and manufactured individually according to customer requirements. Please contact us for more info.

About transformer oil

Transformer oil is used in oil-filled transformers because it has excellent electrically insulating properties. The oil has good stability at high temperatures. It is often a highly refined mineral oil or an ester-based oil but can now also be a bio-based environmental oil.

The function of the oil is to isolate and extinguish arcs. The oil also has a cooling function inside the transformer.

The purpose of a transformer oil filter is to degass/dry the oil and remove any moisture absorbed. This is done at low pressure and at a temperature of about 70 degrees Celsius. The Transorfilter also filters the oil to get rid of particles.

This process of transformer oil treatment is called conditioning and is done in order for the oil to maintain its good insulating properties. Replacing the oil is a worse alternative from a cost and environmental point of view.

Larger degassing system

Transorfilter Sweden also manufactures and develops larger vacuum systems for oil degassing. Example of a customer is ABB Power Transformers, who has a large Transorfilter degassing system for transformer oil in its new-built factory in Ludvika, Sweden since 2019.


Our products are designed with proven technology and approved components. The products are CE-approved with user-friendly manual/documentation. All units are tested and approved according to test protocol values obtained before delivery.