Oil Immersed Transformers Explained: Types, Benefits, and Applications
Nov 10, 2025
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What Is an Oil Immersed Transformer?
An oil immersed transformer houses its core and windings submerged in insulating oil, which serves three critical functions:
Cooling: The oil absorbs and dissipates heat generated during operation.
Insulation: It prevents electrical breakdown by insulating live components.
Moisture Protection: Protects the core and windings from moisture, enhancing longevity.
These robust, efficient transformers are widely used for high-voltage industrial-grade applications and extensive power distribution networks.
Types of Oil Immersed Transformers
Oil immersed transformers are not one-size-fits-all. They come in various types tailored to specific use cases:
1. Oil Immersed Power Transformer
Designed for high-voltage applications, these are commonly used in power plants and substations to manage large-scale power distribution effectively.
2. Oil Immersed Distribution Transformer
Compact and optimized for delivering electricity to localized networks like residential neighborhoods, commercial areas, or small industrial zones.
3. Hermetically Sealed Transformer
These sealed units prevent contamination by keeping the oil completely enclosed, reducing risks of leaks and moisture degradation.
4. Conservator-Type Transformer
Equipped with a conservator tank, these manage oil expansion and contraction, enabling smooth operation under fluctuating loads.
Benefits of Choosing Oil Filled Transformers
- Unmatched Cooling Efficiency
Their oil-cooling system ensures efficient heat dissipation, allowing superior performance under high loads when compared to dry-type transformers.
- High Voltage Capabilities
Ideal for applications requiring consistent performance at high voltages, such as power plants and extensive grid networks.
- Reliability and Longevity
With regular maintenance, these transformers can operate reliably for decades, with the oil acting as a protective barrier against contaminants and moisture.
- Cost-Effective
They typically cost less upfront compared to dry-type transformers. Additionally, their operational energy efficiency helps keep long-term costs low.
Comparing Oil Type and Dry Type Transformers
Understanding the differences between these two main transformer types helps in selecting the right option:
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Feature |
Oil Immersed Transformer |
Dry-Type Transformer |
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Cooling |
Insulating oil and radiators, ideal for high loads |
Air-cooled, better for lower loads |
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Insulation |
Oil-based insulation |
Epoxy resin or other solid materials |
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Voltage Capacity |
High voltage needs (e.g., substations, power plants) |
Primarily for lower voltage applications |
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Environmental Impact |
Potential risks with oil leaks |
Eco-friendly (no oil involved) |
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Cost |
Lower upfront and operational costs |
Higher initial costs, lower ongoing maintenance |
Key Applications of Oil Immersed Transformers
These transformers excel across a variety of industries:
Power Generation
Widely used in power plants to adjust voltage levels efficiently.
Heavy Industry
Ideal for powering heavy machinery and large-scale industrial operations.
Utility Grids
Crucial for wide-scale electricity distribution.
Commercial Facilities
Provides reliable power for shopping malls, office complexes, and hotels.
GNEE Oil Immersed Transformer Product Parameters
| Items | Item |
| Production Descriptions | Oil-Immersed Transformer |
| Reference standards | IEC 60076-11 |
| Capacity | 50-2500kVA or Customized |
| Frequency | 60 / 50Hz |
| Voltage (HV) | 22KV or customized |
| Voltage (LV) | 0.4KV or customized |
| Impedance | 4% |
| Connections (Vector Group) | Dyn11 |
| Tapping Range | ±2×2.5% |
| Core materials | Silicon Steel |
| Winding materials | Aluminum or copper |
| Lightning Impulse Withstand Voltage | IEC standard |
| AC withstand voltage | IEC standard |
| Temperature Rise class | H-class |
| Temperature Rise | 125K |
| Cooling method | AN/AF |
| Delivery Capacity | 300 units per month |
company profile
GNEE TRANSFORMER has strong production capacity and an efficient marketing team.
Our transformer products include 500kV, 400kV, 330kV, 220kV, and 110kV ultra-high voltage transformers, various dry-type transformers/oil immersed transformers/amorphous alloy transformers of 35kV and below, new energy transformers, and prefabricated substations,
Export series: single-phase transformer, three-phase transformer, cylindrical transformer, isolation transformer, control transformer, voltage regulator and other products, And various specifications of special transformers such as grounding transformers, arc suppression coils, Bitcoin transformers, prefabricated cabins, reactors, electric furnace transformers, rectifier transformers, mining transformers, marine transformers, etc.
GNEE TRANSFORMER has successively passed ISO9001, ISO14001, ISO45001, SA8000 system certification. At the same time, 10kV and 35KV level distribution transformers and box type substations have obtained interna- tional Electrotechnical Commission IEC certification, US UL certification, German TUV certification, EU CE certification, Dutch KEMA certification, and GOST certification. Our product sales cover the global market, including 72 countries and regions such as the United States, Europe, Canada, Mexico, etc.
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GNEE Transformer Order specification
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When choosing our company's products, please provide the following data to better serve you. |
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Demander |
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Demander: |
Telephonemethods: |
Fax: |
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Project technical leader: |
Telephonemethods: |
Mailbox: |
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Transformer type selection |
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□Dry transformer {□SC(B) Epoxy resin □SC(B) Non-encapsulated} □American Box(ZGS) {□Terminal type(-Z-) □Ring network type(-H-)} □European Box change(YBM){□ Dry change □Oil change} |
□ Oil-immersed transformer{□ Fully sealed(-M-) □Oil-bearing pillow} □Amorphous alloy transformer{□Dry amorphous □ Oil amorphous} □ Special transformer{Rectifier, Furnace, Mine, Etc} |
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Transformer basic data selection
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Country of use: |
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Phase number: |
□Three-phase(S conventional) □ Monophase □Other( ) |
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Frequency: |
□50Hz(conventional) □60Hz □ Other( ) |
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Transformer oil: |
□#25(conventional) □#45(minimum temperature below-25℃) |
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Rated capacity: |
□( )kVA Conditions of use □Outdoor type □Indoor type |
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Altitude: |
□Less than 1000m(conventional) □1000-2000m □3000m以上 over |
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Rated voltage(High voltage) |
□6kV □10kV □20kV □35kV □66kV □110kV □220kV □Other( ) |
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Rated voltage(Low pressure) |
□0.4kV □0.66kV □10kV □10.5kV □35kV □其他 Other( ) |
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Connected group |
□Dyn11(conventional) □Yyn0 □YNd11 □li0(Single-phase) □Other( ) |
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Impedance(%): |
□4% □4.5% □5.5% □6% □6.5% □7.5% □8% □Other( ) |
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Voltage regulation mode |
□Voltage regulation without excitation(conventional) □On-load voltage regulation(Z) |
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Voltage regulation range |
□±2*2.5% □±5% □±3*2.5% □Other( ) |
Transformer accessory selection
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□Fan □Temperature control{□ Common □With 485 computer interface} □Dry case{□ Ordinary steel sheet □Aluminum alloy » Stainless steel} □Protection level of dry case(□IP20(Conventional) □IP( )} □Dry case height requirements{□None □Requirements[ ]} □ Cable out mode of the dry variable shell {□ Up-and-out □ Up-and-down □Down-in/DOWN-out □Down-in/UP-out □Down-in/DOWN-out □Down-in/ side-out [□Left □ Right-out]} |
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Note: 1. (Dry change requirements s 100kVA transformer does not include fans, such as fans, need to be charged 2. (Oil changes <630kVA transformer does not include temperature control, gas relay, if necessary, need to increase the fee) |
Other special requirements(additional charges apply below)
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Dry transformer |
□Shell and bottom plate{□Ordinary □Fully sealed} □Travel switch □Magnetic lo □Zero sequence transformer □Copper bar to the low voltage cabinet □Protective mesh □Lighting □100kVA or less Fan □Shock absorber |
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Oil-immersed transformer |
□No.45 oil for non-low temperature areas □Designated brand on-load voltage regulator □400kVA and below low voltage outlet OABC phase with wiring terminals □630kVA or below requires temperature control □800kVA or below Low voltage outlet phase 0 requires wiring terminals □630kVA and below must be equipped with gas relay |
GNEE TRANSFORMER Industrial Layout
Asia:China, Philippines, Cambodia, Malaysia, Myanmar, Indonesia, Vietnam, Mongolia, Japan, Taiwan Province, Bangladesh, Sri Lanka, Lebanon, Saudi Arabia, Turkey, Armenia, Iraq, Iran, Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan
Africa:Egypt, Ethiopia, Angola, Botswana, Burundi, Cape Verde, Congo, Guinea, Ghana, Gabon, Zimbabwe, Cameroon, Kenya, Rwanda, Malawi, Mauritius, Mauritania, Mozambique, South Africa, Nigeria, Somalia, Chad, Central Africa
North America: Aruba, Panama, Dominican Republic, Costa Rica, Honduras, Caribbean region,Canada, United States, Mexico, El Salvador, Guatemala, Jamaica
Europe: Bulgaria, North Macedonia, Finland, Norway, Ukraine, Greece, Hungary, Italy, United Kingdom
South America: Argentina, Paraguay, Ecuador, Colombia, Guyana, Venezuela, Uruguay, Chile
Middle East: The Middle East region
Oceania: Australia, Papua New Guinea. Fiji