Kannu International

Transformer oil's primary functions are to insulate and cool a transformer. It must therefore have high dielectric strength, thermal conductivity, and chemical stability, and must keep these properties when held at high temperatures for extended periods.^[1] Typical specifications are: flash point 140 °C or greater, pour point −40 °C or lower, dielectric breakdown voltage 28 kV (RMS) or greater.^[2]

To improve cooling of large power transformers, the oil-filled tank may have external radiators through which the oil circulates by natural convection. Power transformers with capacities of thousands of kVA may also have cooling fans, oil pumps, and even oil-to-water heat exchangers.^[3]

Power transformers undergo prolonged drying processes, using electrical self-heating, the application of a vacuum, or both to ensure that the transformer is completely free of water vapor before the insulating oil is introduced. This helps prevent corona formation and subsequent electrical breakdown under load.^{[citation needed]}

Oil filled transformers with a conservator (oil reservoir) may have a gas detector relay (Buchholz relay). These safety devices detect the buildup of gas inside the transformer due to corona discharge, overheating, or an internal electric arc. On a slow accumulation of gas, or rapid pressure rise, these devices can trip a protective circuit breaker to remove power from the transformer. Transformers without conservators are usually equipped with sudden pressure relays, which perform a similar function as the Buchholz relay.^{[citation needed]}

Servotherm oils have been specially developed for use as heat transfer medium in industrial application. These oils possess high viscosity index, excellent thermal and oxidation stability, low volatility and low vapour pressure to give long service life in well designed heat transfer systems. Servotherm Special is recommended for well designed heat transfer system operating upto 315 C.
Servotherm oils are recommended as a fluid medium in various types of heat transfer system for indirect or secondary heating in industry. The use of these oils provide rapid heating and greater flexibility in heat transfer systems since they possess high specific heat and better thermal conductivity at all temperatures. These oils are suitable for use in both, closed as well as open type heat transfer systems. Servotherm oils have a high resistance to thermal cracking and hence maintain their heat transfer efficiency even when subjected to repeated high and low temperature cycles. The heat transfer system must be thoroughly cleaned and free from contaminants. All traces of dust, rust and residue of welding operations must be removed by flushing. After the flushing oil is drained the system must be free from moisture before it is charged with Servotherm oils.