Your Leading 66KV Oil-Immersed Transformer Supplier
Trust In Grid Co., Ltd. is a professional transformer manufacturer, specializing in the design and production of power transformer, high-voltage switchgear, power distribution equipment, energy storage systems (ESS), magnetic wire, bushing and machining parts. Our power transformers are available in 500KV, 330KV, 220KV, and 110KV models, and are widely used in power utilities, renewable energy systems (solar and wind), industrial facilities, data centers, transportation infrastructure, and OEM applications.
Why Choose Us?
Production Capacity
With 6 factories covering 240,000 m², over 2,000 employees, and 200+ engineers, we support large-scale projects and long-term global supply with more than 30 years of export experience.
Advanced Equipment
We operate a complete set of in-house production equipment, including cutting, winding, CNC machining, vacuum drying, and testing systems, with over 450 machines ensuring stable quality and efficient output.
Quality Control
All products are manufactured and tested in compliance with IEC, IEEE, ANSI, CSA, UL/cUL, CE, and ISO 9001:2015 standards, ensuring reliable performance and smooth international approval.
OEM & ODM Capability
Our engineering team provides OEM/ODM support, including customized design and technical optimization, delivering tailored solutions for utility, industrial, and renewable energy projects.
Specifications of 66KV Oil-Immersed Transformer
|
Parameter |
Specification |
|
Rated Voltage |
66kV (HV) / 6.6–33kV (LV) |
|
Rated Capacity |
10 MVA – 100 MVA |
|
Frequency |
50Hz / 60Hz |
|
Phase |
Three-phase |
|
Cooling Method |
ONAN / ONAF |
|
Insulation Medium |
Mineral oil |
|
Insulation System |
Oil-paper insulation |
|
Temperature Rise |
Winding ≤65°C, Oil ≤55°C |
|
Tap Changer |
Off-circuit or OLTC |
|
Vector Group |
Dyn11 / YNd1 |
|
Impedance |
Typically 8% – 12% |
|
Core Material |
CRGO silicon steel |
|
Installation |
Outdoor / Substation use |
|
Standards |
IEC 60076 / IEEE / ANSI |
Advantages of 66KV Oil-Immersed Transformer
Superior Cooling Efficiency
Insulating oil offers excellent thermal conductivity and heat capacity, enabling the transformer to stay cool during high loads. According to ABB, oil-filled units often outperform dry-type transformers when it comes to sustained overloads.
High Power and Voltage Capacity
Oil-filled transformers can easily handle ratings above 5000 kVA, reaching into hundreds of MVA, making them ideal forgrid guide-scale and industrial use.
Long Lifespan
Thanks to efficient cooling and sealed designs, these units can operate for 25–40 years when properly maintained.
Cost-Effectiveness
Despite periodic maintenance, oil-filled transformers typically offer lower lifetime costs due to better efficiency and durability.
Excellent Overload Tolerance
The oil's thermal mass enables oil-immersed transformers to handle temporary spikes in demand more effectively than dry types.

An oil immersed transformer consists of a core, windings, tank, radiators, and insulating oil.
Core: Built from CRGO steel to minimize hysteresis and eddy current losses.
Windings: Made of electrolytic copper with layered insulation for high dielectric strength.
Tank: Sealed steel enclosure filled with mineral or ester oil for thermal and electrical insulation.
Radiators: Finned structures that increase surface area to improve cooling efficiency.
Difference Between 66KV Oil-Immersed Transformers and Dry-Type Transformers
Performance and Efficiency
When comparing oil immersed5 and dry-type transformers, performance and efficiency are critical factors. Oil immersed transformers use mineral oil for cooling, which significantly enhances their thermal performance. This allows them to handle higher loads and maintain optimal efficiency levels even under strenuous conditions. Conversely, dry-type transformers rely on air cooling, which can limit their efficiency in high-demand scenarios.
Safety and Environmental Impact
Safety considerations are paramount in transformer design. Dry-type transformers have an edge in safety due to the absence of flammable liquids. They are less prone to fire hazards and are ideal for indoor use, including in schools and hospitals. In contrast, oil immersed transformers require diligent maintenance to manage potential oil leaks and associated environmental risks.
Cost Considerations
While the initial purchase price of oil immersed transformers may be lower, long-term cost implications can vary based on maintenance and operational efficiency. These transformers typically have lower operational costs due to their efficient cooling systems. However, the need for periodic oil analysis and potential environmental compliance costs can offset these savings. Dry-type transformers, though potentially more expensive upfront, might offer cost savings in environments where minimal maintenance is beneficial.
Core Lamination Process
The transformer core is manufactured using high-grade CRGO silicon steel to minimize core loss and improve efficiency.
Winding Process (Copper / Aluminum)
Windings are produced using high-conductivity copper or aluminum, depending on project requirements.
Vacuum Drying & Oil Filling
This process ensures optimal insulation performance and long-term reliability.
Testing & Quality Control
Each transformer undergoes strict testing procedures in accordance with international standards.
Final Assembly & Packaging
Final assembly ensures mechanical integrity and readiness for transportation and installation.

Customization Options
Voltage: Optional
Capacity: Optional
Impedance: Optional
Cooling: Optional
OLTC: Optional
MOQ: Customizable
Payment Terms
T.T with 30% downpayment, 70%before shipment.
Paypal or West Union also accept.
Our Service Highlights
Pre-Sales Consultation & Design Support
Early technical engagement to define requirements and deliver optimized solutions.
During Sales & Project Execution
Transparent project management with controlled production, quality tracking, and on-time delivery.
Warranty Advantage
Minimum 2-year warranty on all products, ensuring reliable and risk-free operation.
After-Sales Support
24/7 technical support with fast response, spare parts availability, and training services.
Long-Term Partnership
Lifelong technical support and upgrade guidance for sustained performance.
Packaging & Shipping
Packaging details:
Shockproof foam/moisture-proof film, professional export cartons/wooden crates/pallets.
Final assembly ensures mechanical integrity and readiness for transportation and installation.

Certificates





We're well-known as one of the leading 66kv oil-immersed transformer manufacturers and suppliers in China, also support customized service. Please feel free to buy high quality 66kv oil-immersed transformer made in China here from our factory. Contact us for more details.
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