Tag Archives: dielectric

Which kind of transformer oil to buy?

A great number of manufacturers and distributor of transformer oil operate in the international and national markets.

Transformer oils, a liquid for cooling and insulating power transformers and other high voltage gear, remain an indispensible part of power transmission and generation industry.

In scientific terms, transformer oil is a product of crude oil refining. The properties of transformer oil depend heavily on the quality and parameters of the raw material. Performance of the oil is defined by the positive and negative properties of the crude oil. Chemical composition of the oil is quite complex. It includes the following components: paraffin (10-15%), naphtenes or cycloparaffins (60-70%), aromatic hydrocarbons (15-20%), asphalt (1-2%), sulfuric compounds (<1%), nitric compounds (<0.8%), naphtenic acids (<0.02%) and antioxidation additive (0.5 – 0.5%).

Transformer oils must be highly resistant to oxidation, must not form sludge and emulsify in contact with water. Antioxidation additives are an important component present in virtually all types of transformer oil.

The efficiency of such additive is based on the ability to react with active peroxide radicals, which form in the result of hydrocarbon oxidation reaction and are its primary carriers.

Presence of additives in transformer oil slows aging of the oil. As soon as the additive is depleted, the oil ages in about the same amount of time as an oil without the additive.

The main properties of transformer oil are its viscosity and density. These have a pronounced effect on function of the oil. Higher viscosity may mean better dielectric strength, while also having a detrimental effect on cooling. Optimal kinetic viscosity of the oil at 20C is about 28-30×10-6 m2/second.

Dissipation factor, in turn, is responsible for the oil’s dielectric properties and protects the system from possible short circuits.

These and other properties of transformer oil are improved by the use of high quality crude oil, deep refining and introduction of additives which increase the oil’s oxidation stability and reduce corrosion.

When the oil is significantly oxidized under the influence of water, solids, air and other gases, high temperature etc, the oil should be replaced. If degradation of oil properties is not detected in time, transformers may fail. When the oil decays, it can no longer serve as a dielectric and starts to react with the metal of the transformer tank, hinders cooling and may lead to short circuits.

The following are some of the oils which may be purchase in the local market.

VG type oil is made from paraffinic crude oil by catalytic process with the adition of an antioxidation  additive. It is a good dielectric and is rather stable against oxidation. It is mostly used in higher voltage equipment.

GK type oil is made of sulfuric paraffinic oils by hydrocracking. It also contains ionol antioxidant, which ensures good stability and dielectric properties of the oil. It is another kind of oil used in higher voltage systems.

TKp oil is made from low-sulfur naphtenic crude by acid-alkali purification. The oil also contains the antioxidant. This oil is recommended for equipment with voltage up to 500 kV.

Oil selection depends not only on the type of electric equipment, but also and mostly on the individual requirements of the facility. Most of transformer oils are universal. In all cases, the correct selection of oil type with consideration of local climatic and physical operating conditions ensures reliable and stable operation of power equipment: high voltage transformers and switch gear.