Environmental Farming and Produce

Most oil in engineering is used for lubrication. transformer oil is a different story in that the concern is not so much in reducing friction between working parts but in insulating and cooling an electrified, stationary system. Oil has properties that make it better than water in many applications. Two are that oil does not boil except at high temperature and many oils are more insulating than the plastic coating on most wires. 

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In comparison, water always boils at 100 degrees Celsius unless kept under pressure. Water is a good insulator whenever it is free of dissolved minerals, but if it comes in contact with bare metal it will dissolve small metal particles and become conductive. Certain type of oils, such as mineral oil, do not boil and are not based on organic polymers. Because mineral oil is so inert, it will not degrade even at a temperature far above boiling water.

Most oil has some resistance to electrical conductivity, which should be apparent given that oil is used to manufacture plastic. Lipids and other forms of oil do not mix well with water as they do not have molecular poles. They also do not dissolve minerals well and so cannot easily pass electricity. This is critical for a transformer because its entire purpose is to convert a high voltage to a low voltage using coils of metal.

Most of the time, it is enough that conductive wire or plates be separated by air or even a plain plastic sheet. In the case of transformers, voltage and resistance are high and current would pass through air. The mineral oil creates a barrier between coils of wire and also absorbs the heat that is created by induced electric resistance. The heat transfers through the oil and is then radiated to the outside air.

Mineral oil is desirable for its inert qualities but also because it coats the wires and creates a barrier to all corrosion. That said, transformers with mineral oil do not need any water inside of them. Just as engine oil can be ruined by the presence of water, mineral oil can be degraded if mixed with water because of inevitable reactions with the metal. Transformers should be completely dry before the oil is used.

The good news is that different types of transformer oil is available. Mineral oil can be flammable and is an environmental contaminant. Some organic alternatives have all the most desirable properties while are less flammable and can biodegrade if released to the environment. Technology rises to new demands, but it should be noted that the standard model has worked well for years, and old transformers still hum and do their job after decades.