Alternative Liquid Insulators
The use of mineral oil in conjuction with solid insulation is followed for many years.
Esters
- Ester based fluids have good biodegradability and these have high flash point. The modern complex electrical supply system demands high degree of safety.
- Due to high flash point property esters are more safe. These are particularly used in hazardous areas like chemical, gas plants.
- Caster oil is used as impregnator in capacitors. The electrical properties of ester depends on refining treatment.
- These are popular in high frequency electrical equipments.
- The dielectric constant ranges from the 2 to 3.5.
Vegetable Oils
- Mineral oil, synthetic esters, silicon oil are traditionally used as transformer oils. Mineral transformer oil (hydrocarbons) are obtained from crude petroleum.
- Synthetic oils are prepared by substitution of chlorine atoms in hydrocarbon molecules. These oils have negative impact on environment.
- The traditional vegetable oil is 100% environment friendly and is used as transformer oil in some countries. It shows good dielectric properties when heated (because moisture content is least when it is heated).
- However in cold season the vegetable oil solidifies and may cause problems. So pour point depressants are to be added.
- The vegetable oils are classified as-drying, semidrying, non drying oils.
Silicon Oils
- These are analogus to carbon based organic compounds. These are expensive.
- The thermal stability is better and frequency range is also wide.
- The silicon fluids possess a combination of properties which is not found in the other natural and synthetic liquids.
- The relative permittivity is 2.20 to 2.77 which is low.
- These are used as coolants in radar pulse, radio transformer, air crafts.