Physical, Chemical and Electrical Properties of Good Mineral Insulating Oil

Mar 3, 2020 | Product Applications

Renkert Oil Voltro™ mineral insulating oils work as fluid insulators, coolants and suppressants of corona discharge in transformers. The liquid insulating medium is also used in circuit breakers, high voltage switches, fluorescent lamp ballasts and high-voltage capacitors. This refined petroleum-based mineral oil is stable at high temperatures, even when subjected to thermal, mechanical and electrical stresses. But what makes this oil a perfect insulator and coolant?

We’ll explain some of the vital chemical, physical and electrical properties that make mineral insulating oil a perfect coolant and insulator.

Resistivity

Your ideal mineral insulating oil should have high resistivity to serve as a perfect insulating fluid. You can measure the resistivity of insulating oil by using a dielectric tester. The level of resistivity of such fluids is influenced by temperature, water content, purity and the type of oil additives included in the oil. Renkert Oil takes high-purity virgin base oil and dries it to an exceptionally low water content of less than 15 parts per million, then ensures cleanliness further by fine filtering.

Viscosity

Useful mineral insulating oil should have low to medium viscosity. Mineral oil serves as a coolant. A low viscosity, easy flow oil performs best in removing heat. High viscosity oils simply have lower capacity to transfer the heat. Viscosity, which is the resistance of a fluid’s flow, can be measured by a lab viscometer.

Oxidation and Thermal Stability

Insulating fluids need to have high thermal stability and a low oxidation value for long service life. High thermal instability and a high oxidation rate contribute to the breakdown of mineral insulating oils. The thermal stability of these oils is improved by the high severity refining of the base oil used in Renkert’s Voltro.

Voltro’s excellent stability also reflects high heat transfer ability, low electrical conduction, and negligible sludge and acid formation.

Breakdown Voltage (BDV)

An insulating fluid needs a high breakdown voltage. BDV is high when the mineral insulating oil has a high level of purity. As such, BDV drops in oils with impurities such moisture and contaminants. You can measure BDV by using a breakdown voltage kit. As per industry standards, new insulating oil should have a breakdown voltage of 30kV or more.

Flammability and the Fire Point and Flash Point

Mineral insulating oils should have low flammability to avoid accidental fires. The flammability of such fluids is analyzed by measuring the fire point and flashpoint of the oil. A transformer oil with a high flash point has a low level of flammability. As such, ideal insulating fluids should have a high flashpoint.

Volatility

The volatility of mineral oils is important when this cooling oil temperature rises. Any volatiles will accumulate in the transformer as vapors. As a rule of thumb, ideal insulating oils need to have low volatility, high thermal stability, and low thermal conductivity. The addition of additives can help you in achieving the right levels of thermal conductivity and thermal stability, but the right base oil drives the volatility.

Other Properties of an Ideal Mineral Insulating Oil

Apart from the properties mentioned above, your insulating mineral oil should be visually clear. The oils need to be free from sludge, salt mixes and water, which make the oil cloudy in appearance. The insulating oil should also have low levels of sulfur to prevent corrosion of the metal parts in electric components.

The U.S. leads in producing and consuming petroleum products. Its 18% global share in oil production provides various petroleum products, which include insulating mineral oil. To get the best insulation oil for your application and extend your equipment life, ensure that you use a quality transformer insulating oil. Renkert Oil is a U.S.-based specialty manufacturer of electrical insulating oil. Our Voltro insulating oil meets or exceeds the ASTM D3487 standards so you can be assured of the highest quality and performance.

For more information on obtaining the best mineral insulating oil for your application, please contact us today.