Transformer Oil Relative Permittivity

transformer oil relative permittivity

Transformer oil is still in demand in the electric power industry due to its dielectric qualities. It forms oil gaps between energized parts and permeates cellulose insulation in power transformer. Transformer oil relative permittivity is an important parameter which shows how the oil behaves in an electrical field.

What is transformer oil relative permittivity

Polarization is a process of limited motion or orientation of related charges in a dielectric in an electric field. Relative permittivity is related to polarization. If the dielectric is considered included in an electrical circuit, it is an equivalent of a capacitor. In this case the relative permittivity will be equal to the ratio of the charge of this capacitor and the charge of a vacuum capacitor of the same size, voltage and charge configuration.  

Transformer oil relative permittivity is more than 1. It is only equal to 1 in vacuum. Therefore, relative permittivity indicates the ability of the dielectric to polarize and acquire electrical capacity. It is a nondimensional physical value.

Relative permittivity of various materials differs. As was mentioned above, it is equal to 1 in vacuum. Relative permittivity of gases is close to one, while much higher for materials used in the electrical power industry. The highest relative permittivity is demonstrated by some ceramic materials (tens of thousands). The relative permittivity of transformer oil is approximately 2.1-2.4. When the cellulose insulation of a transformer is impregnated with oil, its relative permittivity approaches 7. This allows the solid insulation to withstand the stresses of transformer operation and the high intensity of the electrical field.    

Controlling the dielectric qualities of transformer oil

The dielectric parameters of transformer oil decrease with contamination by water, gas and oxidation products. Such contamination results in formation of sludge, which settles on the paper insulation with detrimental effects. Polarized substances increase relative permittivity, conductivity and acidity. By analyzing the transformer oil relative permittivity, specific resistance and temperature allows to make conclusions on the degree of oil degradation and prevention of sludge formation on transformer windings. GlobeCore offers several types of equipment to address such issues.

The CMM units remove solid impurities, water and gases from transformer oil by filtration, heating and vacuum treatment.

If the oil has undergone significant change, the CMM-R units are used. Beside filtration, drying and degassing, this unit can restore insulation oil quality by removing aging products and sludge. The process is based on Fuller’s earth adsorbent.

The process in the MCU units uses two other types of adsorbent, specifically zeolite and silica gel. Zeolite ensures good dehydration, while silica gel also removes acids.

The life of transformer insulation system can be extended by checking the dielectric parameters and processing oil to prevent problems. GlobeCore equipment helps to save significant amounts by improving the reliability of power supply.