Uneven heating rarely appears suddenly. It builds slowly as the transformer continues to run under load.
Sometimes the temperature rise stays within operating limits, yet one part of the winding shows more heat than the rest.
That difference tells a story about what the transformer has been experiencing.
Here’s where uneven heating usually begins.
Every winding has its own shape, spacing, and layer pattern. Heat spreads through that layout in a particular direction.
If one area carries a higher current density or tighter spacing, that zone holds more heat. Even small variations during manufacturing can influence how air or oil moves across the conductors.
Over time, the warmer regions age faster. Insulation in those spots grows more brittle, and that difference becomes clearer on temperature scans or thermal imaging.
Transformers manufacturers pay close attention to winding geometry because even slight design changes can alter thermal behavior. By optimizing conductor placement, insulation thickness, and cooling channels, they ensure more uniform heat distribution and extend the operational life of the transformer.
Transformers rarely see a perfectly balanced load. Some phases carry more current because of how equipment operates downstream.
When one phase works harder, it naturally produces more heat. That extra heat does not stay isolated. It spreads slowly through the surrounding coils, making the entire temperature pattern uneven.
If the load profile of a plant shifts throughout the day, these heat pockets change shape and position. The windings adapt, but the material responds in a way that reflects that repeated stress.
Heat inside a transformer depends on how well the cooling medium moves.
If oil flow slows in one part of the coil stack, that area begins to trap heat. The same goes for blocked ducts or uneven air circulation.
Some zones end up cooling less than others, even under normal load. That imbalance builds over time.
As oil in the warmer areas breaks down faster, cooling gets harder where it’s already weakest. The result is a thermal pattern that keeps shifting (and rarely in your favor).
Windings sit under mechanical pressure to prevent movement during energization. Over years of service, that pressure relaxes slightly.
Vibration from load cycles and thermal expansion changes how tightly parts of the coil stay pressed together.
Areas that loosen even slightly tend to heat differently. This happens gradually.
The unit may appear fine on tests, yet an infrared scan reveals a distinct pattern that reflects the coil’s mechanical history.
Oil plays more than one role. It cools, insulates, and carries heat away from the active parts.
As oil ages, its ability to do that changes.
Moisture absorption, oxidation, and suspended particles alter how heat moves through the winding stack. This leads to warmer zones where oil no longer flows with the same clarity or speed.
Monitoring oil quality over time gives early insight into heat imbalance long before it reaches a critical point.
Uneven heating tells you how a transformer has been used, how its load has shifted, and how its internal structure has settled with age.
We treat these patterns as valuable signals when we inspect, upgrade, or recondition transformers in the field.
At our end, during refurbishment or load enhancement work, we look closely at how the heat distributes inside the coil. That helps us tune insulation, cooling pathways, and winding pressure so the transformer can continue performing steadily, even under changing conditions. Get in touch with us to learn more.
