Coupled thermal and hydraulic algebraic models for an open self‐ventilated induction machine

Abstract

The prediction of the thermal behaviour of electric motors in the early stages of their design is a critical factor for reducing time and cost in the design process. In complex machine topologies such as open self-ventilated machines, there are several phenomenas to take into accou n ti no r d e rt op r e d i c tt h ec o r r e c tt h e r m a lb e h a v i o u ro ft h em a c h i n e .I nt h i s study, a thermal model coupled with a hydraulic model is presented. These models provide information of the thermal behaviour of the machine. First, the complete thermal circuit is described, with some emphasis in the specially modelled parts. Then, the heat transfer coefficients for each surface inside the machine are presented, by the use of dimensionless correlations that avoids the need of previous knowledge. Moreover, the hydraulic model of the machine is studied, and also the coupling methodology between the two models is described for both steady state and transient calculations. Finally, the results from the model are validated using the data from two experimental runs, the first one with constant torque and speed, and the other with variable power, in a standardised service cycle, with a difference in the rotor bars and the stator winding below ±10°C.

Analytical thermal model and flow network analysis suitable for open self‐ventilated machines

“…where K adj is adjustment factor, Pr is Prandtl number, which is evaluated at mean fluid temperature, Pr s is Prandtl number evaluated at the temperature of conductor surface, C and m are the constants, which depend on the airflow velocity and are evaluated according to Table 4. Finally, Re Dmax is the maximum Reynolds number and is evaluated as [69] Re…”

“…Moreover, for the machine stator parts located in the outlet of the airflow in indirect contact with the axial flow, the convection coefficient is calculated as [69,70] Nu = 0.17 Re 0.67 .…”

“…The convection coefficient for flat rotational surfaces, for instance, rotor yoke and end rings is calculated as [69,71] Nu = Re a 2 + Re rot 2 ,…”

“…where Re a is the Reynolds number of axial airflow and the Re rot is the Reynolds number due to radial air rotation, and they are calculated, respectively, as [69,71]:…”

Development of analytical thermal analysis tool for synchronous reluctance motors

“…Consequently, LPTN is the main method for fast thermal analysis. Many studies apply the analytical LPTN method for thermal calculation [14, 15]. Mellor in [16] presented one of the earlier studies in this field, where he developed an LPTN for totally enclosed fan cooled (TEFC) induction machine.…”