One-dimensional Lumped-Circuit for Transient Thermal Study of an Induction Electric Motor (original) (raw)

Electrical machines lifetime and performances could be improved when along the design process both electromagnetic and thermal behaviors are taken into account. Moreover, real time information about the device thermal state is necessary to an appropriate control with minimized losses. Models based on lumped parameter thermal circuits are: generic, rapid, accurate and qualified as a convenient solution for power systems. The purpose of the present paper is to validate a simulation platform intended for the prediction of the thermal state of an induction motor covering all operation regimes. To do so, in steady state, the proposed model is validated using finite element calculation and experimental records. Then, in an overload situation, obtained temperatures are compared to finite element's ones. It has been found that, in both regimes, simulation results are with closed proximity to finite element's ones and experimental records. 1. INTRODUCTION The energy conversion inside an electric machine leads inherently to the heat occurrence, essentially due to different proportions of iron and copper losses. In addition, an overheating of a motor is directly linked to the degradation of its performances [1-3]. Thus, in order to reduce such a limitation and avoid the damage of the device, it is necessary to gather the thermal analysis to the electromagnetic study during design process [3-5]. Indeed, the prediction of the temperature distribution in the different parts of the machine allows us to evaluate if the machine will reach the thermal class for which it is being designed and also to check if the supplied air flow of the cooling system is sufficient to a normal operation at rated conditions. Thereby, a satisfactory life span of the machine gathered to an improvement of its performances could be guaranteed. That explains the existence of several prediction methods of temperatures distribution inside electric motors, like: Computational Fluid Dynamics, Lumped Parameter Thermal Circuits, Finite Elements (FE) …, [6-10]. Thermal models based on lumped parameter were developed since a long time. In such models, each node represents a part of the machine and the thermal circuit, in the steady state, consists of thermal resistances and heat sources connected between motor components. For transient analysis, the heat capacitances are additionally used to take into account the ongoing changes. Despite the accuracy of this method, it needs several improvement. Indeed, in [11], the developed thermal model focused only stator parts. Whereas, when the permanent magnets (PM) are placed in rotor, it is necessary to expand the thermal model and take into account this part. In fact, PMs are very sensitive to the temperature rise and the choice of their polarization is directly related to their thermal behaviour. Moreover, in [12], the temperatures obtained by lumped parameter method were a little higher than the measured ones due to the hypothesis considered to elaborate the thermal model.