Transformer Overheating Due to Sustained Overloading

Overloading is the most common cause of rising temperature, occurring when the current draw exceeds the transformer's nameplate kVA rating, leading to excessive I^2R copper losses. This is confirmed by measuring current on all three phases using a calibrated clamp meter and calculating the total kVA demand. If the calculated kVA exceeds the nameplate rating consistently, the transformer is operating beyond its thermal capacity.