Characterization of the thermal performance of expanded slot liner depending on the degree of expansion

Expanded Slot Liner (ESL) is a novel product that is used to electrically insulate and mechanically fix conductors in the slots of electric machines. It is an alternative to the conventional slot liner and epoxy impregnation method. The ESL is inserted into the stator slots together with the electrical conductor. Afterwards, it is expanded thermally, offering process-related advantages, as epoxy impregnation is no longer necessary. This paper characterizes the thermal properties of the 3M ESL-FC190. An experimental setup is used to measure the effective thermal conductivity and the area-specific thermal resistance as a function of the degree of expansion. The thermal conductivity of the material decreases as it expands, which has a negative impact on the thermal performance of the machine. Doubling the layer thickness (0.20 mm to 0.40 mm) leads to a halving of the effective thermal conductivity (0.14 W/mK to 0.07 W/mK) and thus to a factor of four increase in the area-specific thermal resistance (15 Kcm2/W to 61 Kcm2/W). The thermal performance of the electric machine is therefore highly dependent on the degree of expansion, which should be minimized by small joining tolerances in the slot. In the case study conducted, compared to an impregnated machine with a conventional slot liner, the ESL without additional impregnation results in a higher winding temperature.