Oil Immersed Transformer
Sinotech supplies oil immersed distribution transformers engineered for utilities, EPC contractors, and industrial projects that demand proven reliability and fast delivery. With over 30 years of combined manufacturing experience and IEC 60076 / IEEE C57.12 certified production, our transformers are built to perform in real-world conditions — from rural distribution networks to heavy industrial loads and renewable energy integration.
High-grade silicon steel cores reducing no-load losses significantly
Oxygen-free copper windings ensuring superior conductivity and durability
FR3 natural ester insulation option for fire safety applications
Corrosion-resistant tank coatings for coastal and mining environments
Custom Oil Immersed Transformer Manufacturer in China
Our oil immersed transformer portfolio covers 50kVA to 10,000kVA, with primary voltages from 10kV to 35kV and secondary outputs at 0.4kV or custom values. Standard models include S11, S13, and S20 energy-efficient series, designed to meet DOE efficiency levels where applicable. Every unit features high-grade silicon steel cores, oxygen-free copper windings, and premium mineral oil — materials that reduce no-load losses, extend transformer life, and lower total cost.
Primary Voltage
10kV to 35kV
Capacity
50kVA to 10,000kVA
Standards
ANSI/IEEE/DOE/CSA/AS
What Are the Standard Size of Sinotech S13 Oil Immersed Transformer?
| Transformer Capacity (kVA) | High Voltage (kV) | High Voltage Tap Range (%) | Low Voltage (kV) | Rated Frequency (Hz) | Connection Group Model Number | No-load Loss (W) | Load Loss (W) | No-load Current (%) | Noise Level (dB) | Short Circuit Impedance (%) | Gauge A×B (mm×mm) | Dimensions Length×Width×Height (m) | Weight (kg) |
| 30 | 6 6.3 6.6 10 10.5 11 | 52× 2.5 | 0.4 | 50 | D,yn11 Y,yn0 | 80 | 630/600 | 0.5 | 43 | 4.0 | 400×400 | 830x650x950 | 380 |
| 50 | 100 | 910/870 | 0.5 | 43 | 400×400 | 850×680×960 | 420 | ||||||
| 80 | 130 | 1310/1250 | 0.45 | 44 | 400×400 | 870×700×1010 | 520 | ||||||
| 100 | 150 | 1580/1500 | 0.45 | 44 | 400×400 | 900×720×1020 | 580 | ||||||
| 160 | 200 | 2310/2200 | 0.4 | 46 | 550×550 | 1190×770×1090 | 790 | ||||||
| 200 | 240 | 2730/2600 | 0.4 | 47 | 550×550 | 1260×850×1120 | 880 | ||||||
| 250 | 290 | 3200/3050 | 0.35 | 48 | 550×550 | 1300×860×1140 | 1020 | ||||||
| 315 | 340 | 3830/3650 | 0.35 | 48 | 660×660 | 1370×910×1160 | 1220 | ||||||
| 400 | 410 | 4520/4300 | 0.35 | 48 | 660×660 | 1400×920×1220 | 1430 | ||||||
| 500 | 480 | 5410/5150 | 0.3 | 49 | 660×660 | 1530×1000×1280 | 1730 | ||||||
| 630 | 570 | 6200 | 0.25 | 49 | 4.5 | 660×660 | 1610x1060x1320 | 2100 | |||||
| 800 | 700 | 7500 | 0.18 | 50 | 660×820 | 1670x1120x1380 | 2480 | ||||||
| 1000 | 830 | 10300 | 0.17 | 50 | 660×820 | 1720×1160×1400 | 2880 | ||||||
| 1250 | 970 | 12000 | 0.17 | 52 | 660×820 | 1770×1180×1500 | 3500 | ||||||
| 1600 | 1170 | 14500 | 0.16 | 52 | 820×1070 | 1860x1240x1600 | 4130 | ||||||
| 2000 | 1360 | 18300 | 0.16 | 54 | 5.0 | 820×1070 | 1950x1320x1720 | 5420 | |||||
| 2500 | 1600 | 21200 | 0.15 | 54 | 820×1070 | 2070x1400x1800 | 6500 |
Note: Above Is Technical Parameters of 10kV Class S13 Series Energy-saving Oil-immersed Transformer
Custom Oil Filled Transformer Solutions
Custom engineering is where Sinotech stands apart. Whether you need non-standard impedance, dual-voltage taps, special BIL ratings for high-lightning zones, or corrosion-resistant tank coatings for coastal or mining environments, our engineering team delivers drawings within 5-7 working days.
We have successfully supplied transformers for projects in high-altitude regions above 3,000m, desert environments with 50°C temperature swings, and solar farms requiring low-noise and harmonic-tolerant designs.
Each transformer undergoes routine testing — including no-load loss, load loss, impedance, and temperature rise — before shipment. Test reports, CE/IEC certificates, and full export documentation are provided with every order.
Power Distribution Networks
Renewable Energy System
Infrastructure Projects
Advantages of Sinotech Oil Immersed Transformer
High Initial Cost Efficiency
Compared to dry-type models of identical kVA rating, our oil-immersed transformers offer you up to 50% initial purchasing cost savings. We provide highly cost-effective power solutions that lower your upfront CAPEX without compromising total grid performance.
Superior Thermal Oil Cooling
Liquid insulation serves as an outstanding heat transfer medium. Continuous natural oil circulation regulates internal operating temperatures effectively, giving our transformers superior thermal dissipation and higher overload capability for your heavy grid loads.
Unlimited High Voltage Scale
Unlike dry-type units limited to 35kV, our oil-immersed transformers handle high voltages up to 800kV smoothly. We provide versatile power and distribution solutions that perform effortlessly across medium voltage distribution grids and EHV transmission networks.
Extended Operating Lifespan
Constructed with heavy-gauge steel tanks and reinforced core structures, our transformers withstand harsh electrical and mechanical stresses. With routine care, we guarantee a long service life of 25 to 40+ years to maximize your long-term project asset value.
Easy Onsite Maintenance Work
Unlike cast-resin dry-type units, our oil-immersed transformers are fully field-maintainable. Your engineering teams can perform routine oil sampling, filtering, and insulation restoration directly on-site easily, minimizing downtime and simplifying routine servicing.
High Environmental Recycling
Designing for sustainability, our oil-immersed transformers feature highly recyclable copper, core steel, and metal tanks. Paired with biodegradable FR3 vegetable fluids, we deliver smaller equipment footprints and environmentally responsible outdoor power supply.
Oil Immersed Transformer vs. Dry Type Transformer
Oil Immersed Transformer
An oil-immersed transformer submerges its core and windings in dielectric liquid for superior cooling and electrical insulation. It is the global industry standard for high-capacity, outdoor power distribution and high-voltage substation networks.
Core Comparisons:
Insulation & Cooling: Uses dielectric mineral oil or biodegradable FR3 vegetable fluid to submerge active components for high liquid heat dissipation.
Fire Safety & Site: Standard outdoor rating; mineral oil requires safety clearances or oil containment pits for large installations.
Initial CAPEX: Highly economical purchasing cost, saving up to 50% compared to equivalent dry-type transformer models.
Voltage & Capacity: Unlimited voltage and power scaling (capable of handling 10kV up to 800kV+ and 100+ MVA capacities).
Best For:
Outdoor utility distribution grids and primary substations
Centralized solar PV and wind renewable energy farms
Heavy industrial plants and budget-conscious large capacity projects
Dry Type Transformer
A dry-type transformer utilizes solid epoxy resin casting or air insulation without any insulating liquids. It is engineered specifically for indoor commercial environments and high-density urban infrastructure where strict fire safety codes apply.
Core Comparisons:
Insulation & Cooling: Uses solid epoxy resin encapsulation or air insulation with zero liquid fluids, eliminating oil spill risks.
Fire Safety & Site: Highest indoor rating; 100% self-extinguishing and explosion-proof, complying strictly with all indoor commercial building codes.
Initial CAPEX: Higher initial equipment investment, costing nearly double due to specialized solid resin casting processes.
Voltage & Capacity: Restricted primarily to medium and low voltage applications (typically <=35kV and capacities <=5 MVA).
Best For:
Commercial high-rise towers, shopping plazas, and office vaults
Underground subway stations, airport terminals, and data centers
Eco-sensitive urban zones with strict indoor building fire codes
Note: Choosing between oil immersed cost efficiency and dry type indoor safety depends on your local building codes. Sinotech provides free engineering evaluations to help you select the ideal transformer for your site.
How Are Oil Immersed Transformers Classified by Cooling Method?
Heat dissipation is critical to transformer performance and thermal life. Inside an oil-immersed transformer, insulating oil acts as both an electrical insulator and a primary heat transfer medium. Transformers are systematically classified using international IEC/IEEE four-letter cooling codes to match your specific load profiles and climate conditions.
1. IEC/IEEE Four-Letter Cooling Code Format:
- 1st & 2nd Letters (Internal Oil): O = Oil, N = Natural Convection, F = Forced Circulation (Pump)
- 3rd & 4th Letters (External Medium): A = Air, W = Water, N = Natural Flow, F = Forced Flow (Fan/Pump)
2. Cooling Systems Integrated Comparison Matrix:
| Cooling Code | Full Name & Cooling Mechanism | Capacity Range | Maintenance | Best Application |
| ONAN | Oil Natural Air Natural Natural oil convection paired with ambient airflow. | <20 MVA | Low | Rural & Urban Distribution Grids |
| ONAF | Oil Natural Air Forced Natural oil circulation with external cooling fans. | 20 MVA – 60 MVA | Moderate | Utility Sub-stations & Solar Farms |
| OFAF | Oil Forced Air Forced Pump-driven oil circulation with forced-air fans. | 60 MVA – 200 MVA | High | Heavy Industrial & Grid Stations |
| OFWF | Oil Forced Water Forced Forced oil circulation with water heat exchangers. | >200 MVA | High | Hydro Plants & Compact Stations |
3. Practical Cooling Selection Tips & Insights:
ONAN vs. ONAF CAPEX Optimization:
If your project experiences seasonal or midday peak loads, choosing an ONAN/ONAF dual-rated transformer saves 15% to 20% in upfront purchasing costs compared to buying a larger pure ONAN unit.
Automated Smart Fan Control:
Our ONAF cooling fans do not run 24/7. Equipped with PT100 temperature sensors, fans operate in quiet ONAN mode during routine loads and activate automatically only when winding temperatures breach safety thresholds.
Extreme Climate Adaptation:
For desert sites (such as 50°C Middle East ambient temperatures) or high altitudes (>1,000m), we expand radiator surface areas and apply heat-reflective coatings to prevent thermal de-rating.
How Does an Oil Immersed Transformer Work?
Unlike dry-type units that rely on ambient air, an oil-immersed transformer operates as an integrated dual-action system. It combines a magnetic steel core for electromagnetic voltage conversion with a continuous dielectric fluid loop that simultaneously insulates and cools the active components under load.
Electromagnetic Energy Conversion
High-voltage alternating current enters the oil-submerged primary winding, generating a magnetic field in the silicon steel core. This magnetic flux induces a lower, stable secondary voltage tailored to power your equipment safely.
Complete Dielectric Isolation
Because the active core and coil assemblies are completely submerged in high-grade dielectric oil, the liquid penetrates every microscopic void. This creates an impenetrable insulation barrier between live high-voltage conductors and the grounded steel tank, eliminating internal arcing.
Thermo-Siphon Natural Cooling Cycle
As energy transfer generates internal thermal heat, the oil expands and naturally rises toward the top of the tank. It flows into external radiator banks where ambient air cools it down. The cooler, denser oil then sinks back to the bottom, forming a continuous self-driven cooling loop that keeps your transformer operating safely.
High Quality, Reliable, and Long lasting Oil Transformer
Oil immersed transformers feature superior cooling performance which allows higher load capacity during extended operation. The established manufacturing process results in lower initial cost, while standardized maintenance procedures reduce long-term operational expenses. These transformers perform exceptionally well in outdoor and harsh environments, making them the preferred choice for demanding applications worldwide.
30+ Years of Industry Expertise
With over 30 years of combined experience in power electrical engineering, Sinotech brings unmatched technical depth to every project. Our team understands the complexities of different voltage levels, load profiles, and environmental conditions.
Large Manufacturing Capability
Sinotech operates a world-class manufacturing base capable of handling both small custom orders and large-volume utility projects. Our scale ensures consistent quality, competitive pricing, and reliable delivery for clients worldwide.
Comprehensive Product Portfolio
Sinotech offers a complete range of power transformation products, eliminating the need for multiple suppliers. From distribution transformers to prefabricated substations, we cover your entire power infrastructure requirements.
Full Customization Capability
Sinotech engineers custom transformer solutions for high-altitude zones, extreme temperatures, corrosive atmospheres, and renewable energy applications with documented project success.
IEC, ANSI, and CE Certified Quality
Every Sinotech transformer meets stringent international standards. We provide full test reports and certification documentation with each shipment, ensuring regulatory compliance in your target market.
Rigorous Quality Control Process
Quality is built into every step of our manufacturing process. From silicon steel core selection to vacuum oil filling, Sinotech maintains strict controls to guarantee performance, safety, and long service life.
Contact Us Now
OEM Oil Immersed Transformer Supplier
Our production lines support both standard power transformer models and fully custom designs, with annual capacity exceeding 15,000 transformer units. We have successfully executed OEM orders for clients in Southeast Asia, the Middle East, Africa, Latin America and more.
Sinotech welcomes inquiries from distributors, brand owners, and EPC contractors seeking a reliable power transformer manufacturer.
Solar Farm Integration — Chile
“Sinotech designed custom step-up transformers for our 50MW solar plant, handling 35kV output with low-noise requirements. The units passed local inspection without issues. Excellent engineering support.”
Global Clients
