Electrical Machine Slot Thermal Condition Effects on Back-Iron Extension Thermal Benefits

The slot thermal condition is critical for thermal management of high-performance electrical machines, due to the high heat losses and poor heat transfer ability within the slot. With a part of the back iron projected radially downward into the slot, back-iron extension (BIE) shortens the heat dissipation path from the slot coil to the back iron and was proved to be an effective thermal improvement technique. The relationship between BIE thermal benefits and various electrical machines' parameters remains to be investigated. Based on an existing concentrated-wound machine, the relationship between the equivalent slot thermal conductivity (ESTC) and the BIE effectiveness is researched in this article. Utilizing a developed 3-D thermal model, the ESTC effects on the temperature reduction with BIE are indicated with simulation results and verified with experimental tests. BIE is reported to provide temperature reductions ranging from 48 °C down to 18 °C across the plausible range of ESTC values considered. Guidelines are given in the final part to suggest the situations under which BIE is more effective.