Experimental identification of the induction machine frame convection coefficient for varying ventilator speeds

Thermal modeling of induction machines is becoming increasingly important to improve the operational efficiency and performance. Lumped-Parameter Thermal Networks are both flexible and suitable for online use, but their parameters must be well identified to obtain accurate temperature predictions. The convection coefficient between the motor frame and the environment is a particulary difficult parameter to obtain analytically because it summarizes complex fluid flows across the motor. In this paper, the frame convection coefficient and frame convection resistance of a 5.5 kW induction machine is determined experimentally for different external ventilator speeds. It is shown that the average frame convection coefficient increases for increasing ventilator speeds, whereas the convection resistance is inversely proportional to the fan speed. Furthermore, the local convection coefficient changes as function of the axial frame position due to a decreasing local air speed further away from the fan end.Thermal modeling of induction machines is becoming increasingly important to improve the operational efficiency and performance. Lumped-Parameter Thermal Networks are both flexible and suitable for online use, but their parameters must be well identified to obtain accurate temperature predictions. The convection coefficient between the motor frame and the environment is a particulary difficult parameter to obtain analytically because it summarizes complex fluid flows across the motor. In this paper, the frame convection coefficient and frame convection resistance of a 5.5 kW induction machine is determined experimentally for different external ventilator speeds. It is shown that the average frame convection coefficient increases for increasing ventilator speeds, whereas the convection resistance is inversely proportional to the fan speed. Furthermore, the local convection coefficient changes as function of the axial frame position due to a decreasing local air speed further away from the fan end.C