Understanding Winding Hot Spot Rise in Transformers

Winding hot spots in transformers can significantly impact efficiency and longevity. These hot spots are not always located at the highest loss density areas. Instead, their position is influenced by both local heat generation and the cooling conditions present. This insight is essential as it challenges the common assumption that the hottest point is consistently at the top of the winding. Understanding the dynamics of hot spot location is crucial for improving transformer design and operation.

The temperature variations in transformer windings primarily stem from two factors: losses generated in the cables and the cooling conditions surrounding them. When a transformer is loaded, the cables within the windings generate losses that can vary depending on their location. The axial leakage flux—a magnetic field created by the current flowing through the windings—plays a key role in this variation. Cables positioned at different points within the winding experience differing levels of flux, leading to uneven loss distribution.

Three main factors contribute to the uneven distribution of losses in winding cables. First, the axial leakage flux distribution varies across the winding's diameter, resulting in maximum losses at certain points and minimum losses at others. Second, radial leakage flux also contributes to this phenomenon, particularly at the winding ends where significant gaps occur. Lastly, the temperature of the oil surrounding the cables varies with altitude, further influencing resistance and the associated I²R losses in the cables.

In summary, the location and temperature of winding hot spots are influenced by a complex interplay of factors, including load conditions and cooling mechanisms. The findings highlight the need for a deeper understanding of winding characteristics to enhance transformer efficiency and reliability. As transformer technology continues to evolve, more accurate models of hot spot behavior can lead to improved designs and operational strategies.