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What is the best transformer coolant?
Edvard
One of the main sources of losses and
Sie me ns Ene rg y has b uilt a p o we r trans fo rme r with ins ulating liq uid b as e d o n p lant o il fo r G e rman p o we r s up p ly c o mp any EnBW. EnBW is d e p lo ying the trans fo rme r with the alte rnative ins ulating liq uid at the Te inac h s ub s tatio n ne ar Bad Te inac hZave ls te in in the Blac k Fo re s t in o rd e r to inve s tig ate and d o c ume nt its o p e rating b e havio r the re und e r ac tual s e rvic e c o nd itio ns . The trans fo rme r whic h has a p o we r rating o f 40 MVA (107/21 kV) was manufac ture d in the Dre s d e n trans fo rme r fac to ry.
reasons f or temperature rise in various parts of a transf ormer are the magnetic circuit and windings. So what are the actually reasons of heating the transf ormer? Responsible f or heat generation within the transf ormer are core loss, copper loss in windings (I2R loss), stray loss in windings and stray loss due to leakage/high – that’s the answer. To avoid overheating, every transf ormer is using some coolant. I’ll try to name only the main ones with f ollowing description.
Mineral Oil
Mineral oil surrounding a transf ormer core-coil assembly enhances the dielectric strength of the winding and prevents oxidation of the core.
Dielectric improvement occurs because oil has a greater electrical withstand than air and because the dielectric constant of oil (2.2) is closer to that of the insulation. As a result, the stress on the insulation is lessened when oil replaces air in a dielectric system. Oil also picks up heat while it is in contact with the conductors and carries the heat out to the tank surf ace by self convection. T hus a transf ormer immersed in oil can have smaller electrical clearances and smaller conductors f or the same voltage and kVA ratings. Mineral oils used specif ically f or power distribution applications were in commercial production early as 1899. Later, halogenated dielectric f luids-principally askarel f luids noted f or their excellent f ire saf ety propertiesbecame the f luid of choice f or indoor transf ormers.
Askarels
Beginning about 1932, a class of liquids called askarels or polychlorinated biphenyls (PCB) was used as a substitute f or mineral oil where f lammability was a major concern. Askarel-f illed transf ormers could be placed inside or next to a building where only dry types were used previously. Although these coolants were considered nonf lammable, as used in electrical equipment they could decompose when exposed to electric arcs or f ires to f orm hydrochloric acid and toxic f urans and dioxins. T he compounds were f urther undesirable because of their persistence in the environment and their ability to accumulate in higher animals, including humans. Testing by the U.S. Environmental Protection Agency has shown that PCBs can cause cancer in animals and cause other noncancer health ef f ects. Studies in humans provide supportive evidence f or potential carcinogenic and noncarcinogenic ef f ects of PCBs (http://www.epa.gov). T he use of askarels in new transf ormers was outlawed in 1977 (Claiborne, 1999). Work still continues to retire and properly dispose of transf ormers containing askarels or askarelcontaminated mineral oil. Current ANSI/IEEE standards require transf ormer manuf acturers to state on the nameplate that new equipment lef t the f actory with less than 2 ppm PCBs in the oil (IEEE, 2000).
High-Temperature Hydrocarbons
Among the coolants used to take the place of askarels in distribution transf ormers are high-temperature hydrocarbons (HT HC), also called high-molecular-weight hydrocarbons. T hese coolants are classif ied by the National Electric Code as “less f lammable” if they have a f ire point above 300˚C. T he disadvantages of HT HCs include increased cost and a diminished cooling capacity f rom the higher viscosity that accompanies the higher molecular weight.
Silicones
Another coolant that meets the National Electric Code (NEC) requirements f or a less-f lammable liquid is a silicone, chemically known as polydimethylsiloxane. Silicones are only occasionally used because they exhibit biological persistence if spilled and are more expensive than mineral oil or HT HCs.
Halogenated Fluids
Mixtures of tetrachloroethane and mineral oil were tried as an oil substitute f or a f ew years. T his and other chlorine-based compounds are no longer used because of a lack of biodegradability, the tendency to produce toxic by-products, and possible ef f ects on the Earth’s ozone layer.
Esters
Synthetic esters are being used in Europe, where high-temperature capability and biodegradability are most important and their high cost can be justif ied, f or example, in traction (railroad) transf ormers. Transf ormer manuf acturers in the U.S. are now investigating the use of natural esters obtained f rom vegetable seed oils. It is possible that agricultural esters will provide the best combination of hightemperature properties, stability, biodegradability, and cost as an alternative to mineral oil in distribution transf ormers (Oommen and Claiborne, 1996). Silicone oils and high-molecular weight hydrocarbons currently rank as the most popular choices in applications requiring less f lammable f luid. To a much lesser extent, synthetic ester-based f luids and synthetic hydrocarbons are also used. Synthetic ester dielectric f luids have suitable dieletric properties and biodegrade much quicker than mineral oil and hydrocarbon f luids. Due to their high cost compared to other less f lammable f luids, synthetic f luids are generally limited to use in traction and mobile transf ormers, and other specialty applications. A biodegradable f luid represents signif icant potential savings f or utilities because it should simplif y cleanup and remediation plans and procedures. However, the real savings are realized when a transf ormer starts to leak or when there is a spill. T his is particularly true f or utilities in environmentally sensitive areas that have to worry about threats to marine lif e f rom spills or leaks f orm transf ormers located near the water. Resource: Electric power transformer engineering by Dudley L. Galloway and Dan Mulkey
http://electrical-engineering-po rtal.co m/what-is-the-best-transfo rmer-co o lant
What is the best transformer coolant?
Edvard
One of the main sources of losses and
Sie me ns Ene rg y has b uilt a p o we r trans fo rme r with ins ulating liq uid b as e d o n p lant o il fo r G e rman p o we r s up p ly c o mp any EnBW. EnBW is d e p lo ying the trans fo rme r with the alte rnative ins ulating liq uid at the Te inac h s ub s tatio n ne ar Bad Te inac hZave ls te in in the Blac k Fo re s t in o rd e r to inve s tig ate and d o c ume nt its o p e rating b e havio r the re und e r ac tual s e rvic e c o nd itio ns . The trans fo rme r whic h has a p o we r rating o f 40 MVA (107/21 kV) was manufac ture d in the Dre s d e n trans fo rme r fac to ry.
reasons f or temperature rise in various parts of a transf ormer are the magnetic circuit and windings. So what are the actually reasons of heating the transf ormer? Responsible f or heat generation within the transf ormer are core loss, copper loss in windings (I2R loss), stray loss in windings and stray loss due to leakage/high – that’s the answer. To avoid overheating, every transf ormer is using some coolant. I’ll try to name only the main ones with f ollowing description.
Mineral Oil
Mineral oil surrounding a transf ormer core-coil assembly enhances the dielectric strength of the winding and prevents oxidation of the core.
Dielectric improvement occurs because oil has a greater electrical withstand than air and because the dielectric constant of oil (2.2) is closer to that of the insulation. As a result, the stress on the insulation is lessened when oil replaces air in a dielectric system. Oil also picks up heat while it is in contact with the conductors and carries the heat out to the tank surf ace by self convection. T hus a transf ormer immersed in oil can have smaller electrical clearances and smaller conductors f or the same voltage and kVA ratings. Mineral oils used specif ically f or power distribution applications were in commercial production early as 1899. Later, halogenated dielectric f luids-principally askarel f luids noted f or their excellent f ire saf ety propertiesbecame the f luid of choice f or indoor transf ormers.
Askarels
Beginning about 1932, a class of liquids called askarels or polychlorinated biphenyls (PCB) was used as a substitute f or mineral oil where f lammability was a major concern. Askarel-f illed transf ormers could be placed inside or next to a building where only dry types were used previously. Although these coolants were considered nonf lammable, as used in electrical equipment they could decompose when exposed to electric arcs or f ires to f orm hydrochloric acid and toxic f urans and dioxins. T he compounds were f urther undesirable because of their persistence in the environment and their ability to accumulate in higher animals, including humans. Testing by the U.S. Environmental Protection Agency has shown that PCBs can cause cancer in animals and cause other noncancer health ef f ects. Studies in humans provide supportive evidence f or potential carcinogenic and noncarcinogenic ef f ects of PCBs (http://www.epa.gov). T he use of askarels in new transf ormers was outlawed in 1977 (Claiborne, 1999). Work still continues to retire and properly dispose of transf ormers containing askarels or askarelcontaminated mineral oil. Current ANSI/IEEE standards require transf ormer manuf acturers to state on the nameplate that new equipment lef t the f actory with less than 2 ppm PCBs in the oil (IEEE, 2000).
High-Temperature Hydrocarbons
Among the coolants used to take the place of askarels in distribution transf ormers are high-temperature hydrocarbons (HT HC), also called high-molecular-weight hydrocarbons. T hese coolants are classif ied by the National Electric Code as “less f lammable” if they have a f ire point above 300˚C. T he disadvantages of HT HCs include increased cost and a diminished cooling capacity f rom the higher viscosity that accompanies the higher molecular weight.
Silicones
Another coolant that meets the National Electric Code (NEC) requirements f or a less-f lammable liquid is a silicone, chemically known as polydimethylsiloxane. Silicones are only occasionally used because they exhibit biological persistence if spilled and are more expensive than mineral oil or HT HCs.
Halogenated Fluids
Mixtures of tetrachloroethane and mineral oil were tried as an oil substitute f or a f ew years. T his and other chlorine-based compounds are no longer used because of a lack of biodegradability, the tendency to produce toxic by-products, and possible ef f ects on the Earth’s ozone layer.
Esters
Synthetic esters are being used in Europe, where high-temperature capability and biodegradability are most important and their high cost can be justif ied, f or example, in traction (railroad) transf ormers. Transf ormer manuf acturers in the U.S. are now investigating the use of natural esters obtained f rom vegetable seed oils. It is possible that agricultural esters will provide the best combination of hightemperature properties, stability, biodegradability, and cost as an alternative to mineral oil in distribution transf ormers (Oommen and Claiborne, 1996). Silicone oils and high-molecular weight hydrocarbons currently rank as the most popular choices in applications requiring less f lammable f luid. To a much lesser extent, synthetic ester-based f luids and synthetic hydrocarbons are also used. Synthetic ester dielectric f luids have suitable dieletric properties and biodegrade much quicker than mineral oil and hydrocarbon f luids. Due to their high cost compared to other less f lammable f luids, synthetic f luids are generally limited to use in traction and mobile transf ormers, and other specialty applications. A biodegradable f luid represents signif icant potential savings f or utilities because it should simplif y cleanup and remediation plans and procedures. However, the real savings are realized when a transf ormer starts to leak or when there is a spill. T his is particularly true f or utilities in environmentally sensitive areas that have to worry about threats to marine lif e f rom spills or leaks f orm transf ormers located near the water. Resource: Electric power transformer engineering by Dudley L. Galloway and Dan Mulkey
