Thermal and hydraulic design of water-based cooling systems for electrical machines.

Abstract

Thermal management of electrical machines is gaining more and more attention from the research and industrial community, due to the demanding power density and reliability conditions of present and future applications. The aim of this research work is to draw some conclusions about which is the best way of designing and optimizing two types of cooling systems for electrical machines. More precisely, the cooling systems studied use water as a secondary coolant, and are classified by IEC60034 as IC71W and IC81W. These systems are very popular in traction and marine applications. For this purpose, both algebraic and CFD based models have been developed in order to precisely calculate the behavior of the main components of these cooling systems. Once these models have been validated experimentally, they have been employed to derive design and optimization criteria for the systems. Thus, as a first step, the main considerations for the development of an algebraic thermal model for the IC71W cooling system are examined. A detailed classification of the most critical convective correlations and a review of the modelling of the water jacket is given. Once the model is described, the solving procedure and its experimental validation is exposed. Secondly, using the previously validated model a complete design methodology for the water jacket of an IC71W cooling system is proposed. Different elements such as the shaft or the housing are analyzed in order to obtain some criteria for their design. The inclusion of wafters in this kind of cooling systems is examined, proposing an optimum configuration and evaluating the effect of this element on the temperatures of the stator end-windings. Regarding the IC81W cooling system, the same process has been followed. As a first step, both a hydraulic and a thermal model have been developed. The hydraulic model is defined in more detail, because it is crucial to obtain a realistic behavior of airflow inside the machine. After that, a method for the computation and solving of these models and its experimental validation process is presented. Finally, with the developed models, the main elements defining an IC81W cooling system (which is very extended for marine applications), the fan and the primary circuit, are studied. A design methodology for the fan fixed to the shaft is proposed, including the effect of the main parameters defining this element on the airflow and the pressure rise. Furthermore, different elements in the primary circuit are studied, obtaining the thermal behavior of different configurations and determining the best choice in order to reduce temperatures in the active parts of the machine.