Numerical investigation of the air-gap flow heating phenomena in large-capacity induction motors

The thermal characteristics of a large-capacity induction motor were investigated with an air-gap flow temperature that is higher than the stator and winding temperatures. Air-gap flow heating phenomena were defined and classified into three states: under-heating, over-heating, and super-heating. A non-dimensional temperature was suggested to predict the corresponding air-gap flow heating state of a motor. Based on the non-dimensional temperature, the over-heating state is inevitable for a motor with a capacity above 50 kW, and the super-heating state is inevitable for a motor with a capacity above 100 kW. Furthermore, the effects of the over-heating and super-heating states of the air-gap flow on the stator and windings were investigated. Under these two states, the cooling of the stator by the air-gap flow was diminished. Additionally, the winding temperature increased because of the discharged air-gap flow.