THERMAL MODELING OF HIGH-SPEED INDUCTION MACHINES

High-speed electrical machines need effective electromechanical and th ermal design tools because of their mechanical construction, wide oper ation-speed range and high power density. In addition, the practical e xperience associated with the high-speed machines is still rather limi ted. The work presents a thermal-network model for highspeed induction machines. In the modelling, special attention is paid to cooling aspe cts, such as friction losses and convective heat-transfer coefficients . After the theoretical part, the report deals with the experimental r esults obtained by two highspeed motors. The first motor was tested up to a power of 51 kW at 100 000 rpm (water pump) and the second of 34 kW at 50 000 rpm (air compressor). Because of the direct coupling betw een the electrical motor and turbomachine, the losses were evaluated b y calorimetric methods, no-load tests and retardation tests. The frict ion losses measured were 1.4 higher than was expected. On the other ha nd, the cooling losses were much lower than the calculated ones. The m ethod of measurement was not accurate enough to verify the calculated electrical losses. After the loss analysis, temperature-rise tests wer e carried out for the motors. By correcting the friction and cooling l osses according to the measured results, a satisfactory agreement betw een the computed and measured temperature rises was achieved. In the s tator winding, the difference was +/- 15 % for both the motors. The se nsitivity analysis indicated that the accuracy of the thermal model is affected more by estimates for the losses than for the convective hea t-transfer coefficients.