What You Need to Know about Oil-immersed Transformer
Nov 10, 2025
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What Is an Oil-Immersed Transformer?
Transformers change an alternating current (AC) to a higher or lower voltage. A current may need to move to a higher voltage as higher voltages are easier and faster to transport. A current may need to decrease its voltage in residential, commercial, and industrial areas.
One type of transformer is an oil-immersed transformer. Transformers often operate in high-energy, high-heat situations. An oil-filled transformer suspends the transformer of a steel tank filled with oil. The oil cools and insulates the transformer. The device uses convection to move the oil around and through the transformer, cooling it off.
To avoid oil deterioration, transformer oil must be kept at an operating temperature of less than 85°C. For the transformer to run correctly and to prevent excessive oil deterioration, the daily average operating temperature should be around 30°C.
Oil-immersed Transformer: Working Principle
Substations and power distribution areas use oil-immersed transformers. An oil-immersed transformer is similar in design to a regular transformer. It's made up of three main parts: a magnetic core at the center that is surrounded by coils and bushings.
The magnetic core and windings create a magnetic field, allowing the current to pass through. Windings are insulated, with higher voltages needing thicker insulation. Bushings transmit the electricity to its next destination, typically a substation.
Oil-filled transformers change a current to a higher or lower voltage using the principle of induction. This process creates a surplus of heat. The oil helps to keep the transformer from overheating.
The windings and core are submerged in transformer oil. It acts as a cooling agent and an insulator. Convection moves the oil through the windings, coils, and core, keeping the transformer from overheating. Oil is further cooled externally at lower voltage and in an air-cooled radiator with higher voltages.
Types of Oil-Filled Transformers
There are several types of oil-filled transformers. Here are a few of the most common below.
- Single-phase transformers use one pair of windings. It's used in lower-load situations, such as rural areas.
- Three-phase transformers are made up of three pairs of windings. The windings typically go around a core sectioned into three parts. Three-phase transformers are used in higher-load areas and can supply three circuits with energy.
- Power transformers are designed to handle much higher loads. They can step voltages up or down and transmit a current from one place to another.
- Distribution transformers transmit lower voltages from the electrical grid to homes and businesses. They are much smaller than power transformers.
- Pole-mounted transformers are connected to an electrical pole.
- Pad-mounted transformers are mounted to a concrete pad on the ground.
Advantages of Oil filled Transformer
Contractors typically have to choose between oil-filled and dry-type transformers. Both have their advantages. Let's delve into some of the reasons that an oil-filled transformer may be the right choice for you.
First, oil-filled transformers are more affordable. They are often up to half the price of a dry-type transformer with the same capacity.
Oil-immersed transformers tend to be more successful at cooling the transformer than a dry type. Oil is a better cooling medium. They also have a higher voltage capacity. Dry-type transformers operate below 35 kV, while there are no limits with oil-immersed. Oil transformers are more versatile.
Dry-type can typically go from an intermediate location to the power consumption source. Oil-immersed can function as both power and distribution transformers.
Oil-filled transformers are better for the environment, as they are much easier to recycle than dry-type. They are also smaller and work best in outdoor environments in case of an oil spill or other accident.
Maintenance and Safety Considerations for Oil type Transformers
Oil-immersed transformers have maintenance and safety considerations. Keeping your transformer well-maintained can lengthen its lifespan and reduce the risk of safety issues.
You should perform regular visual inspections and cleanings. Check the transformer to ensure that all parts are in good condition and that there is no threat of leaks. Make sure that all fittings are tight. Clean the exterior and interior of the transformer to remove dust, dirt, and other debris.
It's also essential to check the oil frequently. Make sure that the oil is at its proper level. You should also take samples of the oil and have it tested. You don't want to use contaminated oil. Finally, keep an eye on the temperature and air pressure. You want to be sure that the transformer is within the suggested levels.
As with any electrical equipment, there is always a risk of fire. In the event of a fire, it's important to ensure that the oil doesn't leak out from the transformer. Oil can cause the fire to spread, making a hazardous situation even more dangerous.
Conclusion
Oil-immersed transformers provide many benefits and are often a better choice than dry-type transformers. They are efficient and affordable and can run at almost any capacity. While they do require maintenance and pose some safety risks, with the proper care and use, you'll be able to get the most out of your equipment.
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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Fax: |
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Project technical leader: |
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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
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Europe: Bulgaria, North Macedonia, Finland, Norway, Ukraine, Greece, Hungary, Italy, United Kingdom
South America: Argentina, Paraguay, Ecuador, Colombia, Guyana, Mexico, Uruguay, Chile
Middle East: The Middle East region
Oceania: Australia, Papua New Guinea. Fiji