Calibration Techniques of Electrical Machines Thermal Models

Thermal analysis is a key aspect in electrical machine design and in particular for those operating with severe duty where a high-reliability thermal analysis is required. This paper presents a comprehensive analysis of techniques for calibrating generic thermal model of electrical machines. The proposed approach combines two existing experimental methods commonly used in thermal testing of electrical devices. The first method uses a short-duty transient excitation to derive the winding thermal parameters, whereas the second method uses a steady-state excitation to inform thermal parameters related with heat transfer across from the winding body into the machine periphery. Both testing methods are based on a well-defined heat source provided by a dc excitation. In contrast, the existing methods for calibrating thermal models usually combine the winding thermal data predictions and a set of experimentally derived temperatures from dc tests. Such approach however, might be inadequate if not supported by experimental data with a sufficient number of test points. This frequently leads to an under-defined calibration process, with several unknown factors, each of which has a significant impact on the reliability of temperature predictions. The main advantage of proposed approach is the combination of the short-transient and steady-state tests that allows reducing the number of free parameters and it provides a more systematic calibration process. In addition, a detailed test procedure for generic thermal model calibration is presented and discussed.