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Electrical Insulating Oil A.K.A Oil El

Introduction or both to ensure that the transformer is

completely free of water vapor before the Electrical insulating oils were developed and first used late in the 19th century. Nearly all cooling oil is introduced. This helps load bearing in the electric prevent corona formation and subsequent power delivery systems, around the world under load. are filled with some type of this liquid. The liquid functions both as an electrical Oil filled transformers with a conservator (an insulation; suppressing corona and arcing oil tank above the transformer) tend to be and to serve as a . Today, there is equipped with Buchholz relays. on the order of a billion liters of these

petroleum-based insulating oils in use, in transformers, high voltage capacitors,

switch gears and circuit breakers in the entire world.

Transformer oil, or insulating oil, is usually a highly-refined mineral oil that is stable at high temperatures and has excellent

electrical insulating properties.

The oil helps cool the transformer. Because These are safety devices that detect the it also provides part of the electrical build up of gases (such as acetylene) inside insulation between internal live parts, the transformer (a side effect of corona or must remain stable at high an electric arc in the windings) and switch temperatures for an extended period. To off the transformer. Transformers without improve cooling of large power conservators are usually equipped with transformers, the oil-filled tank may have sudden pressure relays, which perform a external radiators through which the oil similar function as the circulates by natural convection. Very large Large transformers for indoor use must or high-power transformers (with capacities either be of the dry type, that is, containing of thousands of KVA) may also have cooling no liquid, or use a less-flammable liquid. fans, oil pumps, and even oil-to-water heat

exchangers. Well into the 1970s, polychlorinated biphenyls (PCBs) were often used as Large, high voltage transformers undergo a dielectric fluid since they are not prolonged drying processes, using electrical flammable. They are toxic, and under self-heating, the application of a vacuum, incomplete combustion, can form highly toxic products such as furan.

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Starting in the early 1970s, concerns about temperature. As a result the original the toxicity of PCBs have led to their chemical properties of transformer oil banning in many countries. changes gradually, rendering it ineffective for its intended purpose after many years. Today, non-toxic, stable silicon-based or fluorinated hydrocarbons are used, where Hence this oil has to be periodically tested the added expense of a fire-resistant liquid to ascertain its basic electrical properties, offsets additional building cost for a and make sure it is suitable for further use transformer vault. or necessary actions like filtration/regeneration has to be done. These Combustion-resistant vegetable oil-based tests can be divided into: dielectric coolant and synthetic pentaerythritol tetra fatty acid 1. (DGA) (C7, C8) esters are also becoming 2. Furan analysis increasingly common as alternatives to 3. PCB analysis naphthenic mineral oil. Esters are non-toxic 4. General electrical & physical tests: to aquatic life, readily biodegradable, and have a lower volatility and a higher flash . Color & Appearance point than mineral oil. .

. Water Content . Acidity (Neutralization Value)

Transformers in electric power distribution . Dielectric Dissipation Factor and transmission systems are expected to . Resistivity function reliably and efficiently and to do so . Sediments & Sludge this for many years. The quality of the oil in . Interfacial Tension a transformer plays an important role in . Flash Point performing this function. Mineral oils used in . Pour Point

electrical apparatus are specified to have . Density certain characteristics which permit . Kinematic Viscosity realizable performance for many years The details of conducting these tests are Transformer oils are subject to electrical available in standards such as and mechanical stresses while a IEC 60296:2003, ASTM D3487:2008, transformer is in operation. In addition there MS 2322:2010 and BS 148:1998, and are contaminations caused due to chemical testing can be done by any of the methods. interactions with windings and other solid insulations, catalyzed by high operating

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The Furan and DGA tests are specifically “Mineral insulating oils complying with the not for determining the quality of requirements of this standard, of the same transformer oil, but for determining any class and containing no additive (see 3.4), abnormalities in the internal windings of the are considered to be compatible with one transformer or the paper insulation of the another and can be mixed in any proportion. transformer, which cannot be otherwise This does not apply to oils containing detected without a complete overhaul of the additives. Where the user wishes to mix transformer. Suggested intervals for this test such oils, a check is recommended to be are: made to ensure that the mixture meets the requirements of this standard” . General and physical tests - bi-yearly

. Dissolved gas analysis - yearly Inhibited oils can be mixed with each other

. Furan testing - once every 2 years, provided they contain the same inhibitor and subject to the transformer being in the content of the inhibitor in the mixture operation for min 5 years. satisfies the requirements.

Compatibility Of The Oils Storage and Handling

As a rule o thumb, new transformer oils Quality and life of transformer oils depends conforming to the same specification and a great deal on the adherence to prescribed class are compatible with each other. For norms while in storage and during handling. example, transformer oils from different The nature of the oils is that they are manufacturers meeting the same IEC 60296 hygroscopic and have a high tendency to grades can be considered as fully readily absorb moisture. compatible with each other. A high level of caution is demanded to Mixing Of Transformer Oils maintain the quality of transformer oils

because or their high sensitive to even New transformer oils can be mixed with minute contamination such as water, polar each other irrespective of the source, compounds and other conducting materials. provided that they satisfy the same standard. This is clarified in all international Field staff storing and handing transformer standards, including IEC 60296, standard oils need to be trained and fully aware of the as extracted below: sensitivity of the products and the precautions to be taken.