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This section provides an overview for oil-filled transformers as well as their applications and principles. Also, please take a look at the list of 14 oil-filled transformer manufacturers and their company rankings. Here are the top-ranked oil-filled transformer companies as of May, 2025: 1.Neeltran, Inc., 2.The Gund Company, Inc., 3.L/C Magnetics.
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Engaged in research on nitride semiconductor growth using the MBE method at Waseda University Graduate School. After graduating from graduate school in 2016, he joined a non-ferrous metal manufacturer.
Engaged in equipment maintenance and engineering work at metal smelting plants. Moved to a chemical manufacturer in 2022. Engaging in similar tasks.
An oil-filled transformer is a transformer that uses oil as an insulating material.
The primary insulating oil is mineral oil. A transformer is a device that uses two coils to convert voltage. These coils, known as the primary and secondary windings, determine the voltage conversion ratio.
There are various types of transformers, but oil-filled transformers are the most widely used in power supply applications.
Oil-filled transformers are used in numerous applications, especially in power transmission and distribution. Electricity produced in power plants is typically high voltage.
This high-voltage power is transmitted over towers and other structures to the transmission lines. Oil-filled transformers convert this high-voltage power for use in low-voltage distribution lines.
The transformed low-voltage power is then distributed to locations such as homes, factories, and commercial facilities. Oil-filled transformers at these sites adjust the voltage to levels suitable for local demands, such as 100 VAC or 200 VAC for households and 200 VAC or 400 VAC for industrial and commercial settings.
An oil-filled transformer comprises an iron core, coils, an oil tank, and insulating oil.
The iron core, situated at the transformer's center, is constructed by laminating silicon steel plates and other materials to create a magnetic circuit. This multilayer structure reduces magnetic losses, enabling efficient power conversion.
The high-voltage and low-voltage windings are wrapped around the iron core. Made from copper or aluminum wire, these windings generate a magnetic field when current flows through them. In step-down transformers, the high-voltage side has fewer windings compared to the more numerous windings on the low-voltage side.
The transformer's components are enclosed within a steel tank, filled with insulating oil. This oil not only insulates the interior but also helps in cooling. Tanks often have fins to facilitate the circulation of the cooling oil and heat dissipation.
Mineral oil is commonly used as the insulating oil in oil-filled transformers. However, environmentally friendly alternatives like sunflower or rapeseed oil are also in use. These oils, while more expensive, help prevent environmental pollution in case of leaks. Monitoring the concentration of organic gases in the insulating oil helps assess transformer conditions. Overheating produces gases like ethylene and ethane, while partial discharge generates acetylene and hydrogen. Acetylene, especially, is an indicator of internal transformer abnormalities and should not be present even in trace amounts.
Oil-filled transformers are categorized into self-cooled and forced-cooled types.
Self-cooled transformers use internal oil and a cooling system for natural heat dissipation. Radiators or similar devices attached to the tank aid in this process. They are commonly used in power transmission and distribution systems.
Forced-cooled transformers have a cooling system that actively circulates oil. This enhanced cooling method is suitable for high-load or high-temperature environments, often involving pumps or fans for oil circulation.
Excessive heating in oil-filled transformers risks insulation failure and potential fires. Therefore, maintaining the operating temperature below the permissible limit is crucial. The general maximum allowable temperature is 105 °C, but it is typically controlled to remain around 95 °C or lower, considering external influences and temperature differences.
Mineral oil in oil-filled transformers, usually classified as Petroleum No. 3, becomes a hazardous material under the Fire Service Law when the volume exceeds 2,000 liters. However, when connected to an electrical circuit, it falls under the Electricity Business Law and is not treated as a hazardous material. If disconnected from the power line, such as during dismantling, it reverts to being a hazardous material. Specific circumstances require consultation with the fire department or relevant authorities.
*Including some distributors, etc.
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The Gund Company, Inc. is a manufacturer and fabricator of composite, thermoplastic, and elastomeric materials, established in 1951 and based in St. Louis, Missouri. The company offers thermosets, thermoplastics, flexibles, and resistance temperature detectors (RTDs). It is AS9100D certified and ISO 9001:2015 compliant and has laboratory and testing capabilities at 8 locations in 5 countries. With R&D engineers, the company develops materials that meet the electrical, physical, and mechanical requirements of its customers in metal processing, aerospace, automotive, power electronics, and medical industries.
Neeltran, which stands for New Energy Transformer and Rectifiers, is headquartered in New Milford, Connecticut. The company is now a part of AMSC and is an ISO-9001-2015 certified designer and manufacturer of its own rectifier transformers and DC rectifiers to customers around the world across diverse industries including aerospace, mining, and petrochemicals. In addition to transformers and DC rectifiers, the company produces reactors and inductors, and turn-key solutions. The company also offers repair, retrofit, rewind, and remanufacturing of rectifiers and transformers.
L/C Magnetics is a US manufacturer and distributor of custom transformers, inductors, and current limiting reactors. It was established in 1990, serving multiple industries, including automotive, aerospace, power generation, telecommunications, and more. The company offers custom dry-type transformers and inductors with various voltage and current ratings, including replacements, buck-boost, obsolete, prototype, and specialized inductors such as high-frequency gapped and military-grade options. It also designs and produces magnetic components, such as coils, chokes, and magnetic shielding. The company has a division called CEHCO that builds DC rectifiers, transformer rectifier assemblies, and custom power supplies.
Fuji Electric Corp. of America, originally founded in 1970 in the USA, is a distributor of products manufactured by the Fuji Electric Group throughout North America and the Americas. The company provides electric solutions for energy, industrial systems, social systems, power electronics, and electronic devices. Fuji Electric Corp. of America offers a wide range of products, such as inverters, circuit breakers, ring compressors, flow meters, and power generators. The company's systems include applications for passenger door automation systems and turbine power generation systems.
Nissin Electric Co., Ltd., established in Kyoto, Japan, in 1917, is a Supplier of electrical energy by substation equipment, and grid connection technology. The company provides factories and office buildings to realize the optimal operation of energy and technical support. They also provide industrial infrastructure, with an emphasis on power system and energy equipment. Their product range includes gas insulated switchgear, storage battery system, vehicle recognition system, high voltage test product and multiple environmental sensors.
DAIHEN Corporation, established in 1919 and headquartered in Osaka, Japan, is a manufacturer of Power Products, Industrial Robots, and RF/MW Generators & Automatic Matching Units for plasma applications. The company provides an extensive array of products, including Oil-immersed Transformer, Cast Resin Transformer suitable for high buildings, public facilities, and hospitals, Power Distribution Equipment such as closed type power distribution boards and remote monitoring systems, as well as Sensors for Robot Welding and Positioners & Sliders. The company also offers various welding & cutting machines, including TIG Welding Machines, Plasma Cutting Machines, as well as Peripheral Devices for Welding.
JHJX Machinery Manufacturing Co. Ltd. was founded in 1992 in the City of Ma An Shan, China, as a manufacturer of hydraulic torque and electric torque wrenches, bolt tensioners, and electric hydraulic pumps. The company's product portfolio comprises hydraulic torque wrenches, pneumatic torque wrenches, electric torque wrenches, hydraulic wrench pumps, and bolt tensioners. These products serve diverse industries, ensuring precise torque control in heavy-duty applications like construction and manufacturing, with wide applications from automotive to electronics assembly, and playing a crucial role in maintaining structural integrity. The company serves various industries, including metallurgy, aerospace, shipbuilding, petroleum, chemical, railway, and mining.
Indcoil, founded in 1968, is an ISO 9000-certified manufacturer of instrument transformers and control transformers in Mumbai, India. The company offers different types of transformers, including cast resin, VPI, oil-filled, converter, and furnace transformers, as well as grounding/earthing, auto, inverter duty, and mounted transformers. Indcoil's products are used in steel plants, cement plants, petrochemicals, and other major industries. The company complies with IS 2026 for routine tests in all transformers manufactured and has received approval from consultants in India, such as MECON, NTPC, EIL, TCE, and DusturCo.
Orecco is a professional manufacturer of electric power distribution and transmission solutions headquartered in Zhejiang Province, China. The company’s product line includes ring main units, outdoor and indoor vacuum circuit breakers, electrical distribution transformers, prefabricated compact substations, and SF6 gas-insulated substations. It operates with six member factories, advanced equipment, and a qualified team of engineers. The company’s products are developed and manufactured to meet IEC requirements and other international standards and are used in diverse applications, including power plants, substations, industrial facilities, commercial buildings, and residential areas.
Shaanxi Hanzhong Transformer Co., Ltd. was established in 1937 and is based in Hanzhong, Shaanxi, China, as a manufacturer of transformers. The product portfolio of the company comprises oil-immersed transformers, distribution transformers, rectifier transformers, furnace transformers, and dry-type transformers. The transformers serve various industries by ensuring efficient electrical power distribution, stepping down high-voltage electricity for safe use, supporting industrial processes like metal production, and guaranteeing efficient power distribution in fire-safe and low-maintenance environments. The company serves various industries, including electrical power distribution, residential and commercial buildings, metal production, electrochemical processes, and indoor industrial applications.
DAELIM BELEFIC Tech Co. Ltd. is a manufacturer of electrical products and equipment founded in 2001 in Beijing, China. The company offers different types of transformers, including single-phase, dry-type, substation, pad-mounted, power, and furnace transformers. It also provides electrical solutions for global customers, such as mobile substations and specialized solutions for earthquake-prone areas, high altitudes, and low temperatures. It fully complies with international standards such as ISO, IEEE, IEC, CSA, AS/NZ, and GOST. It serves commercial, industrial, and residential sectors in Asia, Africa, the Middle East, Europe, America, and Australia.
WEG, founded on 16 September 1961, is the world’s largest manufacturer of commercial and industrial electric motors, gearboxes, automation technologies, power generation equipment, and related equipment. Such products are used in the manufacturing of pumps, compressors, fans, and more. The company started with the motive of manufacturing electric motors, but soon it expanded its services to the manufacturing of electric and electronic components, industrial automation technologies, power and distribution transforms, etc. The company has been awarded various ISO certifications. Different companies, including PAUMAR, GEREMIA and 16 more, are affiliated with the WEG group.
Ranking as of May 2025
Derivation Method| Rank | Company | Click Share |
|---|---|---|
| 1 | Neeltran, Inc. |
17.8%
|
| 2 | The Gund Company, Inc. |
16.0%
|
| 3 | L/C Magnetics |
11.0%
|
| 4 | Fuji Electric Corp. of America |
10.8%
|
| 5 | WEG Electric Corp. |
8.1%
|
| 6 | Indcoil |
4.8%
|
| 7 | Orecco |
4.8%
|
| 8 | Yuebian Electric Co.,Ltd |
4.8%
|
| 9 | Nissin Electric Co., Ltd. |
4.6%
|
| 10 | JHJX Machinery Manufacturing Co.Ltd |
4.2%
|
Derivation Method
The ranking is calculated based on the click share within the oil-filled transformer page as of May 2025. Click share is defined as the total number of clicks for all companies during the period divided by the number of clicks for each company.Number of Employees
Newly Established Company
Company with a History
*Including some distributors, etc.
*Including some distributors, etc.
| Country | Number of Companies | Share (%) |
|---|---|---|
|
United States of America
|
4 | 33.3% |
|
China
|
4 | 33.3% |
|
Japan
|
2 | 16.7% |
|
India
|
2 | 16.7% |
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