There are several reasons why a transformer’s temperature may be too high. These can be due to issues with the transformer itself or external factors.
Causes of Transformer Overheating
Internal Causes
When a transformer operates, it reaches a state where heat generation and heat dissipation are balanced, and the temperature of each part stabilizes. If the oil temperature is higher than usual by 10°C or more under the same conditions, or if the temperature rises despite an unchanged load, it can be considered that there is an internal fault in the transformer.
1，Poor Contact of the Tap Changer:
- During operation, insufficient contact pressure or dirty contacts can increase contact resistance, causing the contact points to heat up.
- This is particularly problematic after reversing the tap changer or during transformer overload.
- Poor contact can be indicated by frequent light gas operations, a rapid drop in oil flash point, or changes in the coil’s DC resistance value.
2，Short Circuit Between Winding Turns:
- Insulation damage between adjacent coil turns can create a closed short-circuit loop, reducing the number of turns in the coil phase.
- This short-circuit loop generates high heat, potentially causing the transformer to overheat or burn out.
- Causes include manufacturing defects, insulation aging, mechanical damage, and over-voltage or over-current conditions.
- Indicators include rising oil temperature, boiling oil sounds, deteriorated oil quality, and the transition from light gas to heavy gas action.
3，Iron Core Silicon Steel Sheet Short Circuit:
- External damage or insulation aging can damage the insulation between silicon steel sheets, increasing eddy currents and causing local overheating.
- Damaged insulation through core screws can also lead to eddy currents.
- Mild issues can cause a general rise in oil temperature, while severe issues can trigger frequent light gas actions, a drop in oil flash point, and eventually heavy gas actions.
4，Lack of Oil or Blockage in Heat Pipes:
- Transformer oil serves as insulation, cooling, and arc extinction medium. Lack of oil or blocked heat pipes reduce oil circulation speed, causing the transformer to overheat during operation.
External Causes
1，Severe Overload:
- During operation, core hysteresis loss, eddy current loss, and coil copper loss convert to heat, raising the temperature.
- Iron loss is constant and cannot be reduced, whereas copper loss increases with load, leading to higher temperatures under severe overload.
2，Blocked Air Inlet and Outlet or Serious Dust Accumulation:
- The air inlet and outlet of the transformer room facilitate air convection. Blockages or dust accumulation worsen heat dissipation, causing operational overheating.
- If the air temperature measured 1.5m to 2m from the transformer oil tank, at half the tank height, is 8-10°C higher than the surrounding air, ventilation needs improvement.
3，Failure in the Cooling Circulation System:
- Besides heat pipe cooling, transformers use forced air cooling, forced oil circulation, and water circulation. Any failure or poor performance in these systems will cause the transformer to overheat.
Summary
Maintaining the proper function of a transformer involves monitoring both internal and external factors that contribute to temperature rise. Regular maintenance, proper ventilation, and ensuring efficient cooling systems are crucial to preventing transformer overheating and ensuring safe and efficient operation.