Heat transfer in a through-ventilated induction motor

The effects of varying the cooling air flow and its distribution on the heat transfer in a high-voltage, strip-wound, four-pole induction motor are reported. The flow variations were achieved by altering the motor speed, by removing the wafters, by increasing the flow resistance of the motor air inlets, or by the insertion of heat transfer augmentation devices in the stator-frame ducts. Heat transfer coefficients were deduced from the measurement of input power, and from miniature heat flux gauges attached to the surfaces. The overall heat transfer coefficient on the end-winding at the air outlet end (the fan end) was roughly double that at the air inlet end, the converse of the situation for lap and concentric wound motors. Large spatial variations in the end-winding local heat transfer coefficients occurred. This is attributed to the open nature of the winding which results in the individual loops behaving as separate bodies, each with a flow pattern dependent upon the angle of the approaching flow. There was a large increase in the overall heat transfer coefficient on the winding at the fan end when the wafters were removed. The use of transverse ribs in the statorframe ducts was found to enhance heat transfer.