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Transformer oil
Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled wet transformers, some types of high-voltage capacitors, fluorescent lamp ballasts, and some types of high-voltage switches and circuit breakers. It functions to insulate, suppress corona discharge and arcing, and serves as a coolant.
Most often, transformer oil is based on mineral oil, but alternative formulations - with different engineering or environmental properties - are growing in popularity.
Transformer oil's primary functions are to insulate and cool a transformer. It must therefore have high dielectric strength, thermal conductivity, and chemical stability, and must keep these properties when held at high temperatures for extended periods. Typically, they have a flash point greater than 140 °C (284 °F), pour point less than −40 °C (−40 °F), and a dielectric breakdown at greater than 28 kVRMS. To improve cooling of large power transformers, the oil-filled tank may have external radiators through which the oil circulates by natural convection. Power transformers with capacities of thousands of kilovolt-ampere may also have cooling fans, oil pumps, and even oil-to-water heat exchangers.
Power transformers undergo prolonged drying processes, using electrical self-heating, the application of a vacuum, or both to ensure that the transformer is completely free of water vapor before the insulating oil is introduced. This helps prevent corona formation and subsequent electrical breakdown under load.
Oil filled transformers with a conservator oil reservoir may have a gas detector relay like a Buchholz relay. These safety devices detect the buildup of gas inside the transformer due to corona discharge, overheating, or an internal electric arc. On a slow accumulation of gas, or rapid pressure rise, these devices can trip a protective circuit breaker to remove power from the transformer. Transformers without conservators are usually equipped with sudden pressure relays, which perform a similar function as the Buchholz relay.
Mineral oil is generally effective as a transformer oil, but it has some disadvantages, one of which is its relatively low flashpoint versus some alternatives. If a transformer leaks mineral oil, it can potentially start a fire. Fire codes often require that transformers inside buildings use a less flammable liquid, or the use of dry-type transformers with no liquid at all. Mineral oil is also an environmental contaminant, and its insulating properties are rapidly degraded by even small amounts of water. Transformers are well equipped to keep water outside the oil for this reason.
Pentaerythritol tetra fatty acid synthetic and natural esters have emerged as an increasingly common mineral oil alternative, especially in high-fire-risk applications such as indoors due to their high fire point, which are over 300 °C (572 °F). They are biodegradable, but are more expensive than mineral oil. Natural esters have lower oxidation stability in the 120C oxygen saturated test of approximately 48-hours compared to 500-hours for Mineral oils, and are therefore used in closed transformers.
Hermetic seals are important for larger transformers due to thermal expansion and contraction. Mid-size and large power transformers will typically have a conservator and employ a rubber bag with the use of natural ester to reduce oxygen ingress and prevent the natural ester from experiencing a faster oxidation than utilities are accustomed to with mineral oils. Silicone or fluorocarbon-based oils, which are even less flammable, are also used, but they are more expensive than esters.[citation needed]
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Transformer oil AI simulator
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Transformer oil
Transformer oil or insulating oil is an oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled wet transformers, some types of high-voltage capacitors, fluorescent lamp ballasts, and some types of high-voltage switches and circuit breakers. It functions to insulate, suppress corona discharge and arcing, and serves as a coolant.
Most often, transformer oil is based on mineral oil, but alternative formulations - with different engineering or environmental properties - are growing in popularity.
Transformer oil's primary functions are to insulate and cool a transformer. It must therefore have high dielectric strength, thermal conductivity, and chemical stability, and must keep these properties when held at high temperatures for extended periods. Typically, they have a flash point greater than 140 °C (284 °F), pour point less than −40 °C (−40 °F), and a dielectric breakdown at greater than 28 kVRMS. To improve cooling of large power transformers, the oil-filled tank may have external radiators through which the oil circulates by natural convection. Power transformers with capacities of thousands of kilovolt-ampere may also have cooling fans, oil pumps, and even oil-to-water heat exchangers.
Power transformers undergo prolonged drying processes, using electrical self-heating, the application of a vacuum, or both to ensure that the transformer is completely free of water vapor before the insulating oil is introduced. This helps prevent corona formation and subsequent electrical breakdown under load.
Oil filled transformers with a conservator oil reservoir may have a gas detector relay like a Buchholz relay. These safety devices detect the buildup of gas inside the transformer due to corona discharge, overheating, or an internal electric arc. On a slow accumulation of gas, or rapid pressure rise, these devices can trip a protective circuit breaker to remove power from the transformer. Transformers without conservators are usually equipped with sudden pressure relays, which perform a similar function as the Buchholz relay.
Mineral oil is generally effective as a transformer oil, but it has some disadvantages, one of which is its relatively low flashpoint versus some alternatives. If a transformer leaks mineral oil, it can potentially start a fire. Fire codes often require that transformers inside buildings use a less flammable liquid, or the use of dry-type transformers with no liquid at all. Mineral oil is also an environmental contaminant, and its insulating properties are rapidly degraded by even small amounts of water. Transformers are well equipped to keep water outside the oil for this reason.
Pentaerythritol tetra fatty acid synthetic and natural esters have emerged as an increasingly common mineral oil alternative, especially in high-fire-risk applications such as indoors due to their high fire point, which are over 300 °C (572 °F). They are biodegradable, but are more expensive than mineral oil. Natural esters have lower oxidation stability in the 120C oxygen saturated test of approximately 48-hours compared to 500-hours for Mineral oils, and are therefore used in closed transformers.
Hermetic seals are important for larger transformers due to thermal expansion and contraction. Mid-size and large power transformers will typically have a conservator and employ a rubber bag with the use of natural ester to reduce oxygen ingress and prevent the natural ester from experiencing a faster oxidation than utilities are accustomed to with mineral oils. Silicone or fluorocarbon-based oils, which are even less flammable, are also used, but they are more expensive than esters.[citation needed]