7/29/2019 Transformer Oils

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DIELECTRIC MATERIALSClassified into three types:Solid dielectric materials

Elemental solid dielectrics Ionic non-polar solid dielectrics Polar solid dielectrics

Liquid dielectric materials Mineral insulating oils Synthetic insulating oils Askarels Fluorinated liquids Synthetic hydrocarbon liquids Chlorinated hydrocarbon liquids Organic esters Silicon oils Vegetable oils

Gaseous dielectric materials Air, Nitrogen, Hydrogen, sculpture

hexafluoride

The requirements of Transformer oils are as follows: To provide high dielectric strength

To permit good transfer of heat To be of low viscosity To have high flash point To prevent corrosion To protect the papers from dirt and moisture It must be free from inorganic acid, alkali and corrosive

sulphur It must be free from sludging under normal operation

Transformeroils (insulating oils) have replaced toxic PCB(polychlorinated biphenyl). Transformer oil consists of four majorgeneric classes of organic compounds namely:

Paraffins Naphthenes Aromatics Olefines

All of these are hydrocarbons and hence insulation oil is called apure hydrocarbon mineral oil. For good fresh insulating oil, it isdesirable to have more of saturated Paraffins, less of Aromatic

and/or Naphthenes and none of Olefines.

TESTS OF TRANSFORMER OILMoisture test

Acidity testElectrical strength testSludge resistance test

Liquid-Filled Transformers Oil-filled Transformers :

Oil-filled transformers primarily use mineral-based oil and cellulose paper (Kraft or Aramid) in their insulation systems. Thisproven combination exhibits outstanding thermal and dielectric properties at a relatively low cost. So popular and effective are theseunits, that all other transformer designs are judged in relation to them. They are still unparalleled in terms of purchase cost, amongall the options available. The inherent weakness of a mineral oil-filled transformer, of course, is flammability; which is why oil-filledtransformers are usually restricted to outdoor installations, or indoor installations that have elaborate means of fire protection.Typical Applications:

Oil-filled transformers, thanks to their lower purchase costs, find applications in literally every sort of power distribution. Of late, the

awareness of the fire risks associated with mineral oil-filled transformers has created a movement towards safer alternatives thatuse non-flammable, biodegradable liquids, or even dry-type transformers.Non-Flammable Liquid-Filled Transformers

Polychlorinated biphenyl (PCBs) were produced in large quantities starting as early as the 1930s, in response to theelectrical industry's need for a less flammable substitute for mineral oil as a cooling/insulating fluid for transformers. Severalindustrial incidents, however, brought the toxicity of PCBs to the fore. As confirmed organic pollutants, PCBs were banned by thelate 1970s. A number of alternatives have since surfaced - major ones being silicone, perchloroethylene, high temperaturehydrocarbons, and mixtures of oil with perchloroethylene. The first high molecular-weight hydrocarbon-based fluid (HMWH), wasintroduced in 1975. This fluids possesses similar dielectric properties as mineral oil, provide remarkable levels of fire-resistance, anddo not have undesirable environmental fallouts.Typical Applications:

Non-flammable liquid-filled transformers can be installed indoors and outdoors, close to buildings, walkways and rooftops. Usually,no additional infrastructure is required to address issues like fire safety.Biodegradable Fluid Liquid-Filled Transformers

Animal fats and vegetable oils offer substitutes that are significantly less harmful to the environment than petroleum oils. However,vegetable oils were not used in transformers for a long time; a fluid which could be stable in the transformer environment andavailable in the required quantities was simply not available.Transformer manufacturers have since worked on transformer designs that utilize vegetable oil-based dielectric fluids. Comparablein size and electrical performance to conventional liquid-filled units, these transformers are filled with the less flammable dielectricfluids mentioned above. The immediate advantages of biodegradable fluids are clear: higher fire and flash points, thus reducingflammability concerns. The other, and perhaps more long-term advantage, is the fluid's biodegradability: it has demonstrated highenvironmental assimilation (over 95% in less than a month) - and it has the virtue of coming from a toxin-free resource.

Typical Applications:Biodegradable fluid liquid-filled transformers find application in wind turbines, and other indoor and outdoor areas of heightenedenvironmental and safety sensitivity.

Transformer oil, the Petroleum based mineral insulating oil is refinedspecifically to meat the requirements of electrical insulation and heattransfer. The amount of oil contained in transformers significantly. Itmainly depends upon the power rating of transformer. Silicon oil can

withstand higher temperatures than mineral oils.

The basic raw material for the production of Transformer oil is a low viscosity lube termed asTransformer oil base stock (TOBS), which isnormally obtained by fractional distillation andsubsequent treatment of crude petroleum. TOBS isfurther refined by acid treatment process to yieldTransformer oil.