Oil Immersed Transformer
Our oil-immersed transformers are fully customizable, spanning capacities from 30 kVA to 31,500 kVA at voltages up to 38.5 kV. Whether your application calls for standard distribution, amorphous alloy, 3D triangular wound core, or intelligent on-load tap-changing models, each unit is engineered to meet the precise demands of your grid.
Built with vacuum oil-filling technology and fully sealed corrugated tanks, every transformer delivers efficient heat dissipation and strong short-circuit resistance. Advanced core materials reduce no-load losses by up to 75%, extending reliable performance across the full service life.
Custom Transformer Solutions
Voltage: 6-38.5 kV
Capacity: 30-31,500 kVA
Frequency: 50/60 Hz
Access Top Quality Transformer Solutions to Elevate Your Power Projects
Reliable Oil Immersed Transformer For Sale
S13(20, 22)-M Series Energy-Efficient Oil Immersed Distribution Transformer
Standard 10kV distribution transformers using high-permeability grain-oriented silicon steel with a fully sealed corrugated tank structure. For units with a capacity of 800 kVA and above, we provide an optional gas relay for real-time internal fault detection and system protection.
Voltage: 6-11 kV
Capacity: 30 kVA – 2,500 kVA
Vacuum oil-filling process
Fully sealed maintenance-free
Optional gas relay(≥800kVA)
S13(20,22)-M.RL Series Three-Dimensional Triangular Wound Core Transformer
A specialized series featuring a 3D triangular core structure that eliminates traditional magnetic circuit joints. This symmetrical design achieves a 10-15 decibel noise reduction and minimizes stray magnetic fields, making it ideal for noise-sensitive residential environments.
Voltage: 6-11 kV
Capacity: 30 kVA – 2,500 kVA
Ultra-quiet operation
No-joint magnetic circuit
Fully symmetrical structure
S(B)H15(21, 25)-M Series Amorphous Alloy Oil Immersed Transformer
High-performance units utilizing 0.025 mm amorphous alloy ribbons to slash no-load losses by 75% compared to S11 models. Combined with low-voltage copper foil windings, this series offers superior short-circuit resistance and the highest energy efficiency for utility grids.
Voltage: 6-11 kV
Capacity: 30 kVA – 2,500 kVA
75% no-load loss reduction
Amorphous alloy ribbon core
Copper foil winding technology
SZ18 On-Load Tap-Changing Energy-Saving Power Transformer
Designed for 35kV sub-transmission networks, these heavy-duty transformers feature integrated on-load tap changers (OLTC). They maintain a stable secondary voltage by automatically adjusting the tap position during load fluctuations in industrial and rural grids.
Voltage: 35 kV – 38.5 kV
Capacity: 3,150 kVA – 31,500 kVA
On-load voltage regulation
Remote monitoring capabilities
Heavy-duty substation design
SZ13-M·ZT Intelligent On-Load Tap-Changing Transformer
An intelligent solution that automatically adjusts its capacity rating to match real-time power demand. It effectively solves “over-sizing” issues in areas with significant seasonal or diurnal load variations, drastically reducing operational losses during off-peak periods.
Voltage: 6-11 kV
Capacity: 30 kVA – 630 kVA
Automatic capacity regulation
Smart grid terminal integration
Energy loss optimization
YB-D Series Underground Compact Substation
A modular underground substation consisting of a buried transformer unit and a surface-level LED advertising lightbox. The enclosure features a fully welded, submersible design with an automatic drainage system to ensure safe operation during extreme flooding events.
Voltage: 6-11 kV
Capacity: 30 kVA – 1,600 kVA
Submersible waterproof structure
Integrated media lightbox
Minimal surface footprint
10 kV S13(20, 22)-M.RL Series Sample Specifications — Full Data for All Series Available Upon Request
Specifications
| Capacity (kVA) | High Voltage (kV) | High Voltage Tap Range (%) | Low Voltage (kV) | Frequency (Hz) | Connection Group Number | No-load Loss (W) | Load Loss (W) | No-load Current (%) | Short-circuit Impedance (%) | ||||
| S13 | S20 | S22 | S13 | S20 | S22 | ||||||||
| 30 | 6 6.3 6.6 10 10.5 11 | ±5 ±2 × 2.5 | 0.4 | 50 | Dyn11 Yyn0 | 80 | 70 | 65 | 630/600 | 505/480 | 455/430 | 0.3 | 4 |
| 50 | 100 | 90 | 80 | 910/870 | 730/695 | 655/625 | 0.25 | 4 | |||||
| 80 | 130 | 115 | 105 | 1310/1250 | 1050/1000 | 945/900 | 0.22 | 4 | |||||
| 100 | 150 | 135 | 120 | 1580/1500 | 1265/1200 | 1140/1080 | 0.21 | 4 | |||||
| 160 | 200 | 180 | 160 | 2310/2200 | 1850/1760 | 1665/1585 | 0.19 | 4 | |||||
| 200 | 240 | 215 | 190 | 2730/2600 | 2185/2080 | 1970/1870 | 0.18 | 4 | |||||
| 250 | 290 | 260 | 230 | 3200(3050) | 2560/2440 | 2300/2195 | 0.17 | 4 | |||||
| 315 | 340 | 305 | 270 | 3830/3650 | 3065/2920 | 2760/2630 | 0.16 | 4 | |||||
| 400 | 410 | 370 | 330 | 4520/4300 | 3615/3440 | 3250/3095 | 0.16 | 4 | |||||
| 500 | 480 | 430 | 385 | 5410/5150 | 4330/4120 | 3900/3710 | 0.15 | 4 | |||||
| 630 | 570 | 510 | 460 | 6200 | 4960 | 4460 | 0.15 | 4 | |||||
| 800 | 700 | 630 | 560 | 7500 | 6000 | 5400 | 0.14 | 4.5 | |||||
| 1000 | 830 | 745 | 665 | 10300 | 8240 | 7415 | 0.13 | 4.5 | |||||
| 1250 | 970 | 870 | 780 | 12000 | 9600 | 8640 | 0.12 | 4.5 | |||||
| 1600 | 1170 | 1050 | 940 | 14500 | 11600 | 10440 | 0.11 | 5 | |||||
| 2000 | 1360 | 1225 | 1085 | 18300 | 14640 | 13180 | 0.1 | 5 | |||||
| 2500 | 1600 | 1440 | 1280 | 21200 | 14840 | 13360 | 0.1 | 5 | |||||
Discover Core Advantages of Transformers to Optimize Your Power Layout
Remarkable Advantages of Unicore Oil Immersed Transformers
High Efficiency and Low-Loss Performance
The core utilizes grain-oriented silicon steel or amorphous alloy ribbons to minimize magnetic resistance. Our S22 and Amorphous Alloy series reduce no-load losses by up to 75% and no-load current by 80%. These units meet the latest global energy-efficiency standards, significantly lowering long-term operational costs for utility grids and industrial plants.
Hermetically Sealed and Leak-Free
We employ fully sealed corrugated tank structures and vacuum oil-filling technology to eliminate air and moisture from the windings. This design prevents oil oxidation and aging, ensuring zero oil leakage during the equipment’s lifecycle. The hermetic seal provides maintenance-free performance while preserving superior dielectric strength.
Superior Heat Dissipation and Overload
Oil-immersed cooling provides higher thermal conductivity compared to dry-type insulation. The corrugated tank design maximizes surface area for natural heat dissipation, while forced air cooling (ONAF) is available for high-capacity units. This ensures stable operation under sustained load and superior short-circuit withstand capability in harsh environments.
Marine-Grade Anti-Corrosion Protection
The enclosures undergo rigorous acid washing, phosphating, and three-layer paint processes, including marine-grade anti-corrosion coatings. For specialized environments, 304 stainless steel tanks are available. This provides exceptional resistance to salt spray, moisture, and UV radiation, making them ideal for coastal, underground, and industrial areas.
Comprehensive Safety and Fault Protection
Units are equipped with advanced protection components, including pressure relief valves and multi-functional oil temperature indicators. For units above 800 kVA, gas relays (Buchholz) are standard to provide real-time fault alerting and automatic tripping. These multi-layered safety mechanisms prevent tank rupture and protect the entire power system.
Smart Monitoring and Remote Control
Integrated intelligent temperature controllers and GPRS-enabled load monitoring terminals support real-time data acquisition. Users can remotely track temperature, load levels, and power factor via integrated distribution management systems. This digital integration simplifies grid management and reduces on-site inspection requirements and costs.
Trusted by Clients Across Industries and Continents
Unicore Oil Immersed Transformer Global Cases
Oil Immersed Transformer to Malaysia
Urban Infrastructure– Power Grid
800 kVA
Oil Immersed Transformer to Gambia
Municipal Substation– Public Utility
2,500 kVA
Oil Immersed Transformer to Ecuador
Industrial Park– Power Distribution
1,250 kVA
UNICORE ELECTRIC
Transformer Solutions
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Our Global Partners Network
Real Experiences from Transformer Professionals Who Trust Unicore
What Our Clients Say
High Reliability, S13 Series Distribution Transformer
“We sourced the S13-M series for a grid upgrade project in a remote mining area. The build quality of the vacuum-filled, hermetically sealed tanks is impressive, providing excellent protection against harsh outdoor dust and moisture. For our larger 1250 kVA units, the optional gas relay adds a critical layer of safety that our engineers highly value. A very solid, dependable product.”
Robert
Australia
⭐⭐⭐⭐⭐
Exceptional Quietness, S13-M.RL 3D Wound Core Series
“For our latest residential development, noise reduction was a non-negotiable requirement. The S13-M.RL three-dimensional wound core units delivered exactly what was promised. The noise level is noticeably lower—at least 10 decibels quieter than the traditional units we previously used. It’s the perfect solution for urban substations where silence and efficiency are priorities.”
Stefan
Germany
⭐⭐⭐⭐⭐
Reliable Power Solutions for Global Industrial and Infrastructure Projects
Applications of Oil Immersed Transformer
Utility Power Distribution
1. Utility distribution substations for smart urban networks
2. High-voltage transmission substations for regional power grids
3. Global grid expansion and network modernization projects
Industrial Facilities
1. Heavy-duty industrial manufacturing and massive assembly plants
2. Mining operations and large resource extraction sites
3. Petrochemical complexes and integrated steel production mills
Renewable Energy
1. Utility solar photovoltaic (PV) energy power plants
2. Onshore and offshore wind energy generation farms
3. Integrated large-scale battery energy storage systems (BESS)
Commercial Infrastructure
1. Critical high-tier data centers and server facilities
2. Modern hospitals and advanced medical healthcare complexes
3. International airports and large commercial shopping centers
Infrastructure Projects
1. Urban railway traction and metro transit systems
2. Commercial ports and global maritime logistics hubs
3. Municipal water and specialized sewage treatment plants
EV Charging & Microgrids
1. High-power DC fast-charging electric station networks
2. Public transport fleet vehicle charging infrastructure systems
3. Smart community and sustainable remote area microgrids
Understanding the Key Differences to Make the Right Choice
Oil Immersed Transformer vs. Dry Type Transformer
| Feature | Oil Immersed Transformer | Dry Type Transformer |
| Cooling Medium | Insulating Oil | Air |
| Core Protection | Fully submerged in oil (Anti-corrosive) | Exposed to air (Sensitive to humidity) |
| Installation | Primarily Outdoors (Excellent weather resistance) | Indoors (Safe for crowded areas) |
| Power Capacity | Higher (Suitable for large-scale grids) | Moderate (Local distribution) |
| Maintenance | Moderate (Periodic oil checks) | Low (Dusting and simple inspections) |
| Fire Safety | Lower (Requires fire-isolated areas) | Higher (Self-extinguishing materials) |
| Initial Cost | Lower (More economical for high ratings) | Higher (Higher material/production cost) |
When Should You Choose an Oil Immersed Transformer?
While dry-type transformers are ideal for indoor safety, Oil-Immersed Transformers are the superior choice in the following scenarios:
Outdoor & Harsh Environments:
When the installation is outdoors or in regions with high humidity, salt spray, or heavy dust (such as mining or coastal areas).
Budget-Conscious Large Projects:
When you need a high-capacity unit (above 2500kVA or high voltage) and want to minimize the initial investment.
Heavy Industrial Power Demand:
For factories, steel mills, or petrochemical plants where the transformer must handle continuous heavy loads and high-power fluctuations.
Grid & Renewable Energy Integration:
Perfect for long-distance power transmission and boosting power in wind or solar farms where efficiency is paramount.
Note: We manufacture both oil immersed and dry type transformers. Unsure which one fits your project? Contact our team anytime for expert selection advice!
A Strategic Guide to Balancing Performance, Reliability, and Site Conditions
How to Choose the Right Type of Oil Immersed Transformer?
Choosing the correct oil-immersed transformer is a strategic engineering decision that must account for application environments, cooling methods, and long-term maintenance constraints. We act as your technical partners, offering comprehensive consulting services—from analyzing your specific load profiles and site climate to designing a customized transformer solution. We ensure that your investment is optimized for maximum efficiency, safety, and longevity.
1. Key Selection Factors (Beyond Voltage)
To avoid operational inefficiencies or costly replacements, we look deeply into your project’s parameters:
- Voltage Class & Power Capacity: We don’t just look at your current power needs. We analyze your peak demand, continuous load profiles, and reserve capacity for future grid expansion. This ensures your transformer won’t be overloaded as your facility grows.
- Cooling Requirements & Ambient Climate: Heat is the enemy of transformer lifespan. Depending on your local climate, we match the cooling design to your thermal load. For smaller capacities, we recommend ONAN (Oil Natural Air Natural) for energy-saving, silent operation. For medium to large transformers handling high peak loads, we design ONAF/OFAF (Forced Air/Oil circulation) systems with automated fans or pumps to actively manage extreme temperatures.
- Installation Environment & Footprint: Will the unit be indoors or outdoors? For coastal areas or heavy industrial zones, we can apply special anti-corrosion coatings. If your urban substation has strict space constraints, our engineers will design a compact layout that still meets ventilation standards.
2. The Core Decision: Hermetically Sealed vs. Conservator-Type
Understanding the structural design is the most critical step. Based on your maintenance capabilities, we typically recommend one of two main structures:
Hermetically Sealed Transformers
Design:
Uses a fully sealed corrugated tank without a conservator. The flexible corrugated fins automatically expand and contract to adjust to oil volume changes caused by temperature fluctuations.
The Advantage:
100% isolates the insulating oil from ambient air. This completely prevents moisture ingress and oil oxidation, halting insulation degradation and ensuring the unit remains virtually maintenance-free.
Best For:
Compact urban distribution substations
Renewable energy systems (Solar/Wind)
Remote or unmanned sites
Conservator-Type Transformers
Design:
Features an external oil conservator mounted on top. Excess oil from thermal expansion safely flows into this tank, which breathes through a silica gel breather to keep the internal environment dry.
The Advantage:
This highly scalable structure safely manages massive oil volume expansions in ultra-high-capacity units. It also easily integrates with advanced smart monitoring systems for precise health diagnostics.
Best For:
High-voltage grid transmission substations
Heavy industrial load centers
Large-scale power generation plants
3. Application Matching & Custom Solutions
Every project is unique, and our factory is equipped to deliver:
- For Urban Substations & Renewables: We highly recommend Hermetically Sealed + ONAN designs for a compact footprint, ultimate reliability, and zero maintenance headaches.
- For Heavy Industry & Power Grids: We engineer robust Conservator-Type + ONAF/OFAF transformers that guarantee thermal stability and uninterrupted power under the most demanding massive loads.
Note: Contact our engineering team today with your project specifications, and let us design the optimal power solution for you.
Best Practices for Maximizing Lifespan and Minimizing Risks
Safety Considerations for Oil Immersed Transformer
Keeping your transformer well-maintained is essential to lengthening its lifespan and significantly reducing the risk of safety issues. A proactive approach to maintenance ensures long-term reliability and secure operations.
1. Routine Inspections and Cleaning
Visual Checks: Perform regular visual inspections to ensure all components are in good condition and all fittings are tightly secured.
Leak Prevention: Actively inspect the unit to guarantee there is no threat of oil leaks.
Debris Removal: Clean the exterior and interior of the transformer regularly to remove dust, dirt, and other debris that could impact its performance.
2. Oil Quality and Operational Monitoring
Oil Levels & Testing: Frequently check that the insulating oil is at its proper level. Take regular oil samples for testing to ensure the transformer is not operating with contaminated oil.
Temperature & Pressure: Keep a close eye on operational temperature and internal air pressure, ensuring the transformer always operates within the manufacturer’s suggested safe limits.
3. Fire Safety and Containment
Fire Risk Awareness: As with any high-voltage electrical equipment, there is always an inherent risk of fire.
Leak Containment: In the event of a fire, it is critical to ensure that oil does not leak from the transformer. Escaping oil can cause the fire to spread rapidly, making a hazardous situation even more dangerous.
Note: Have questions about maintaining your transformer or experiencing unexpected issues? Our expert engineering team is always on standby. Feel free to contact us anytime for troubleshooting, professional guidance, and fast solutions to keep your equipment running safely and efficiently.
Why Choose Unicore
Your Trusted Partner in Power Solutions
Built for grid, industrial, and infrastructure sectors, our oil immersed transformers combine 75% energy savings with zero-leakage reliability. With 30 years of expertise, we deliver high-ROI power solutions that excel in the world’s harshest environments.
Tailored Engineering Solutions
Custom voltage, capacity, and core materials (Amorphous/3D Wound) designed to match your specific grid requirements and climate.
Proven Operational Stability
100% factory pre-testing and lightning impulse verification ensure long-term stability and high dielectric strength in harsh environments.