Thermal effects of stator potting in an axial-flux permanent magnet synchronous generator

Axial-flux machines often have certain problems with heat transfer as shrink fitting of the stator core in the housing is not an option, unlike in the case of radial-flux machines. In this paper, we study how potting of the stator affects the thermal behavior of a 100 kV A axial-flux generator. The axial-flux permanent magnet (PM) generator is of a one-rotor-two-stator type construction. A liquid cooling system is applied on the stator frame, and the potting material in the end-winding region thermally connects the end winding to the housing heat sink. The design principle of the cooling system is presented in detail. Simplified thermal models based on Computational Fluid Dynamics (CFD) are used to analyze the temperature distribution through the machine. The theoretical results are verified by measurements. For comparison, one stator of the prototype generator is potted with Ceramacast 675-N material while the other stator is not potted. In each stator there are 14 Pt-100 temperature sensors. As the temperature values between the potted and unpotted stator are compared, it is found that the temperatures differ from each other by approx. 10% at the end windings under load condition. The application of the potting material also provides the rotor cooling.