Dry type distribution transformers play a crucial role in electrical power systems, converting power to higher or lower voltages depending on the application. This process generates heat, increasing the temperature of the transformer’s internal components, particularly its windings. Distribution transformer's temperature rise is the average temperature of the windings in Celsius above the ambient temperature when the transformer is operating at full capacity.
Choosing the correct insulation and C-rise rating for a transformer is critical. It ensures optimal performance, energy efficiency, and safety, especially in applications requiring precision and reliability.
Distribution Transformers typically feature one of three C-rise ratings: 80°C, 115°C, or 150°C. Lower C-rise ratings correlate with increased efficiency and cooler operation, making them ideal for critical applications like hospitals, schools, renewable energy systems, and manufacturing facilities.
Transformers with lower C-rise ratings also produce less waste heat, minimizing ventilation and cooling requirements. Opting for a transformer with an appropriate C-rise rating and high-quality insulation not only maximizes efficiency but also extends the unit's lifespan.
| Insulation system temperature | Average winding temperature rise limits at rated current | Maximum hot spot winding temperature ℃ |
| 105 (A) | 60 | 130 |
| 120 (E) | 75 | 145 |
| 130 (B) | 80 | 155 |
| 155 ( F) | 100 | 180 |
| 180 (H) | 125 | 205 |
| 220 (C) | 150 | 245 |
While many dry-type transformers are designed to function reliably for several decades, exposure to temperatures exceeding their tolerable limit can lead to accelerated insulation wear and significantly shorten their lifespan. Transformers with lower efficiency tend to produce more heat, which leads to a higher temperature rise — commonly referred to as C-rise. In contrast, transformers with greater efficiency and performance typically exhibit a lower C-rise.
C-rise represents the average temperature, measured in Celsius, by which a transformer’s windings exceed the surrounding ambient temperature when operating at full load. This temperature increase is caused by power losses in the transformer’s core and conductors. The type of insulation system used determines the maximum temperature the transformer can handle while maintaining efficient operation.
dry type transformers with low C-rise ratings are especially suitable for applications demanding high reliability and long-lasting performance.
Several elements impact a transformer’s operating temperatures, including:
The type of insulation used in a transformer plays a critical role in its ability to manage heat. Different insulation materials have varying capacities to dissipate and transfer heat, influencing the C-rise levels a transformer can tolerate.
The choice of winding material is often application-specific. Copper windings offer superior conductivity and are optimized for lower current densities, making them suitable for high-efficiency applications. On the other hand, aluminum windings are a more cost-effective option for lower voltage requirements. Additionally, advanced winding techniques can help minimize C-rise, improving overall performance.
Selecting a transformer with an appropriate rating for its intended use is essential. Transformer ratings, expressed in volt-amperes (VA), indicate the unit’s capacity to deliver power to a specific load. Overloading a transformer can cause excessive heat buildup, reducing its efficiency and lifespan.
The environment in which a transformer is installed has a significant effect on its ability to manage heat. Proper airflow around the unit is essential, especially for enclosed transformers with air vents. Placing transformers too close to walls or other equipment can block ventilation, resulting in higher operating temperatures.
The insulation in a power transformer plays a pivotal role in its performance, safety, and reliability. Insulation is assigned a class rating that represents the highest temperature it can withstand. These ratings range from Class 105 to Class 220, based on standards set by the National Electrical Manufacturers Association (NEMA).
For instance, insulation with a Class 220 rating accommodates a maximum 150°C temperature rise, plus a 30°C hot spot allowance, and a 40°C ambient temperature. The total equals 220°C, representing the insulation's thermal tolerance.
Operating a transformer beyond its insulation rating can lead to overheating, degradation, and safety risks. Conversely, using high-quality insulation ensures:
At Varelen Transformers, we prioritize quality by using premium insulation materials. Unlike some manufacturers that cut corners, we use only top-tier insulation for all our transformers.
DuPont™ Nomex® Insulation
SG-200 Fiberglass Insulation
In addition to superior insulation, Varelen Transformers uses laminated steel cores and 100% copper windings for maximum efficiency. Every transformer is manually assembled and hand-wound, ensuring top-notch quality control.
Insulation not only affects efficiency and safety but also contributes to the transformer’s environmental footprint. At Varelen, we design transformers with materials that align with modern sustainability goals, ensuring minimal waste during production and long-lasting operational benefits.
Insulation is a critical component of any dry-type transformer, influencing its efficiency, safety, and lifespan. At Varelen Transformers, we combine premium-grade materials with advanced engineering to deliver reliable, high-performance solutions for diverse applications. Whether you need a low C-rise transformer for enhanced efficiency or a durable unit for high-stress environments, we have the expertise to meet your needs.
Partner with Varelen Transformers to experience the best in transformer technology, tailored to your unique requirements.
