How does a transformer oil temperature indicator work?

A top oil temperature indicator typically uses a bulb or sensor in a thermal well to measure oil temperature, driving a dial, alarms, or SCADA inputs. Some systems add a heater element proportional to load current to simulate hot spot behavior, improving protection against overheating. The indicator supports cooling control, alarm thresholds, and load management. Trending top oil temperature helps detect cooling system issues, blocked radiators, fan or pump failures, and abnormal losses.