What is the normal temperature range for a transformer?
What are the reasons for the excessive temperature rise of a transformer?
The excessively high temperature rise of a transformer may be caused by various reasons, including:
In terms of load
Overload operation
When the load carried by a transformer exceeds its rated capacity, the losses in the transformer's windings and core will increase sharply. According to the formula P=I²R (where P is the power loss, I is the current, and R is the winding resistance), an increase in load current causes copper loss (winding resistance loss) to increase by a factor of the square of the current. For example, if the load current becomes twice the rated current, the copper loss will become four times the original.
Overload may also increase the magnetic flux density in the iron core, leading to a corresponding increase in iron loss (hysteresis loss and eddy current loss). Long-term overload operation will cause the transformer temperature to continue to rise, exceeding the normal range.
Change in load nature
If the power factor of the load decreases, for example, from a higher power factor close to 1 to a lower power factor (such as 0.5 - 0.7), the transformer needs to provide a larger reactive current. Reactive current also generates losses in the windings. Although it is not directly used for doing work, it increases the total current of the transformer, which in turn leads to increased copper losses and excessive temperature rise.
Cooling system malfunction
Insufficient cooling oil: Oil-immersed transformers rely on transformer oil for heat dissipation. If the oil level is too low, some windings and cores cannot be properly cooled. For example, transformer oil leakage due to poor sealing, or natural loss due to long-term neglect of oil level inspection, can all result in insufficient cooling oil to meet the heat dissipation requirements.