How do dry transformers handle high voltage and current without overheating?

Dry transformers handle high voltage and current without overheating through several key design features and principles that ensure efficient operation and effective heat management. These include the transformer’s construction, insulation, cooling methods, and material choices. 
Magnetic Core: The core of a dry transformer is typically made of high-quality silicon steel or other magnetic materials that are designed to carry the magnetic flux generated by the primary winding. This core material helps to ensure efficient energy transfer between the windings and minimizes losses, which helps prevent excessive heat generation.
Low Losses: High-performance core materials are designed to minimize core losses (hysteresis and eddy current losses), which are key contributors to heat in transformers. Lower losses in the core mean less energy is wasted as heat.
Conductors: The windings in dry transformers are made from high-conductivity materials, typically copper or aluminum. These materials allow efficient current flow, reducing electrical resistance and thus minimizing heat generated by resistive losses (I²R losses).
Insulation: Dry transformers use specially designed insulating materials (such as resin, epoxy, or VPI – vacuum pressure impregnation) to prevent electrical shorts between turns of the winding. Proper insulation also helps to manage the internal temperature by improving the thermal resistance of the windings.
Natural Air Cooling (AN): Many dry transformers rely on natural convection cooling (referred to as AN – Air Natural), where the ambient air around the transformer dissipates heat. The design of the transformer is optimized to allow air to circulate around the windings and core, which helps cool the transformer as it operates.
Transformers are often designed with ventilation openings or cooling ducts to improve airflow and enhance heat dissipation.
Forced Air Cooling (AF): In some cases, especially for high-capacity or high-power transformers, forced air cooling is used. This involves using fans or blowers to move air over the transformer’s core and windings more rapidly, which increases the rate of heat transfer and keeps the transformer from overheating.
Forced cooling systems are typically used when a transformer operates at higher load levels and generates more heat.
Thermal Class Insulation: Dry transformers use thermal class insulation materials rated to withstand higher temperatures. For example, epoxy resin used in many dry transformers can handle temperatures up to 220°C, depending on the insulation class. These high-temperature ratings help ensure that the transformer does not overheat even when subjected to high currents and voltages.
Thermal Overload Protection: Some dry transformers are equipped with temperature sensors or thermal protection devices that monitor the temperature of the windings. If the temperature rises beyond a safe threshold, these devices can trigger alarms or automatic shutdowns to prevent damage due to overheating.
Load Regulation: Dry transformers are designed to operate efficiently within a certain range of load conditions. When a transformer is underloaded, it may not generate enough heat to cause concerns, while overloading can result in excessive heat. Dry transformers are typically rated for specific load conditions, and operating them within these limits ensures that they don’t overheat.
Current Limiting: The design of dry transformers ensures that the current flowing through the windings stays within manageable limits, preventing excessive heating. This is often achieved by designing the transformer for the specific voltage and current requirements of the application, ensuring that the electrical load is balanced.