Cooling and Heat Transfer

Abstract

During the operation of an electrical machine, heat is generated due to power losses in electric and magnetic circuits and mechanical (rotational) losses. To ensure a long operational life for the machine, these losses must be removed as far as possible from the machine so that the temperature limitations established for the machine materials, such as insulating materials, lubricants and PMs are complied with. In addition to the consideration of the machine’s operational life, a lower operating temperature reduces extra winding losses introduced by the temperature coefficient of the electric resistance — eqn (3.47). Whereas extensive research has been devoted to the thermal studies of conventional electrical machines, AFPM machines have received very little attention [118, 219, 231, 232]. Owing to the fact that AFPM machines possess a relatively large air gap volume and quite often have multi-gaps, the general perception is that AFPM machines have better ventilation capacity than their radial field counterparts [48, 96]. Since the external diameter increases rather slowly with the increase of output power, i.e. [96], the existing heat dissipation capacity may be insufficient to cope with excessive heat at certain power ratings, so that more effective means of cooling have to be enforced. Thus, quantitative studies of the heat dissipation potential of AFPM machines with vastly different topologies is important