Mineral Oil Ardan is using Transformer's Minerl oil manufactured by Ergon. An American leading oil refinery that manufacture and sells transformer mineral oil. Oil is used to cool the transformer, because it also provides part of the electrical insulation between internal live parts, transformer oil must remain stable at high temperatures for an extended period. To improve cooling of transformers, the oil-filled tank have external radiators or cooling fans through which the oil circulates by natural convection. Transformers undergo prolonged drying processes, using the application of a vacuum, making sure that the transformer is completely free of water vapor before the cooling oil is introduced. This helps prevent corona formation and subsequent electrical breakdown under load. Transformer oils are subject to electrical and mechanical stresses while a transformer is in operation. In addition there is contamination caused by chemical interactions with windings and other solid insulation, catalyzed by high operating temperature. As a result the original chemical properties of transformer oil changes gradually, rendering it ineffective for its intended purpose after many years. Hence this oil has to be periodically tested to ascertain its basic electrical properties, make sure it is suitable for further use, and ascertain the need for maintenance activities like filtration/regeneration. The oil tests include: Color & Appearance Breakdown Voltage Water Content Acidity (Neutralization Value) Dielectric Dissipation Factor Resistivity Sediments & Sludge Interfacial Tension Flash Point Pour Point Density Kinematic Viscosity.