Experimental investigation of the thermal contact resistance in shrink fit assemblies with relevance to electrical machines

Thermal design and modelling in electrical machines is important because it allows a proper choice of materials, avoids de-rating of the machine and eliminates excessive safety factors thus achieving higher current densities. In high current density electrical machines, particularly those making use of liquid cooled housing jackets for heat removal, the stator to housing thermal contact resistance is on the main heat removal path of the electrical machine. So far it has always been assumed that this parameter is dependent on the shrink fit manufacturing procedure of the machine. However this paper provides experimental evidence showing that the thermal contact resistance not only varies with shrink fit pressure but is also affected by heat flux and temperature. Hence the common notion that the thermal contact resistance is a constant value set during the machine assembly, and that during thermal design this value can be applied across the whole operating range of the machine is an over simplification. The paper presents arbitrary correlations showing the variation of thermal contact resistance with heat flux and shrink fit pressure and compares the measured values with values quoted in the literature.