1. Due to eddy currents or insulation damage of the through core screws used for clamping the iron core, the oil temperature of the transformer will increase. After the insulation of the through core screw is damaged, the insulation between the through core screw and the silicon steel sheet is also damaged. At this time, a large current flows through the through core screw, causing the screw to heat up and also raising the oil temperature of the transformer.

2. Short circuits between local layers or turns of the winding, faults in internal contacts, increased contact resistance, and high resistance short circuits on the secondary circuit can also cause an increase in oil temperature.