The analysis of the infrared excitation winding surface temperature measurement on a synchronous hydro-generator in rotation

Excitation winding temperature is used for determination of the dynamic limit in the P-Q diagram of a synchronous generator. The surface temperature of an excitation winding can be measured by an infrared (IR) thermometer. Due to rotation, the IR thermometer absorbs thermal radiation from the excitation winding on the salient pole and from the interpolar space as well. These two surfaces can have different temperature or emissivity, which both affect the amount of the thermal radiation radiated towards the sensor of the IR thermometer. Irradiation read by the sensor is therefore the average irradiation of a rotating rotor. This irradiation results in the temperature that differs from the pole surface temperature. The difference depends on the interpolar space size, emissivity and temperature. The effect of the interpolar space can be cancelled if the IR thermometer is positioned at a certain angle with respect to machine´s main axis. Temperature sensors have been mounted on the rotor to measure the excitation winding surface temperature for comparison.