摘要:

Though thermal considerations are one of the major limitations to the output obtainable from electrical machines, the thermal design of machines and their cooling circuits seems seldom to be accorded quite the attention that is normally directed to the electrical and magnetic circuits. There are various ways in which the designer of an electric motor handles the losses occurring in the different parts of the machine: generally, by dissipation from the surface, but also by conduction from areas that are difficult to cool adequately to those where this is easier to achieve, and, where appropriate, by using the thermal capacity of the machine to even out peak or cyclic thermal loads. The superior dissipation obtained by blowing air over a surface rather than relying on natural convection and radiation results in all but the smallest motors relying on some form of forced cooling, in which cooling air is blown over the surfaces to be cooled by shaft-driven fans. Though the cooling-air paths of electric motors are often complicated by the need to cool all the many component parts of the machine in which losses occur and therefore in which heat is generated, nevertheless an application of quite simple considerations of fluid flow yield acceptable methods of estimating the resistance of the air paths. Similarly, the behaviour of the common types of fans used on electrical machines is developed, and, by way of illustration, graphical solutions are indicated for a few typical motor cooling circuits.

DOI:10.1049/ij-epa.1978.0007

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The paper deals with the application of an unconventional electrical machine for circulating molten aluminium in reverberatory furnaces. Its design is based on the classical jumping-ring principle, and it incorporates some hitherto less known aspects of open magnetic circuits and of the concepts of flux spreading. Results of trials using a prototype machine are given, and the metallurgical and other benefits which accrue from its use are discussed. To maintain the electromagnetic integrity of this machine at liquid-metal temperature (> 700°C), a study of its thermal behaviour is made using a mathematical model. This model is subsequently verified by experimental observations. Proposals are made for the future use of some unconventional electrical machines in an aluminium remelt plant.

DOI:10.1049/ij-epa.1978.0009

出版商:IEE    

年代:1978

数据来源: IET

摘要:

This paper formulates proposals for an induction-motor design suitable for a wide variety of inverter applications. Special attention is paid to retaining the advantages of induction motors, but the wide range of inverter waveforms and strategies complicates this attempt. The analysis leads to a design which, although not fully optimal, is easy to realise and gives good results over a wide application area. A preliminary discussion is presented on leakage reactance, to inquire by what means and to what extent it should be modified. The use of an external reactance is put forward. Skin-effect losses in stator and rotor conductors are analysed and suitable design adaptions are defended. Skewing and its impact on leakage reactance and losses are discussed.

DOI:10.1049/ij-epa.1978.0010

出版商:IEE    

年代:1978

数据来源: IET

摘要:

Hysteresis loops produced in oriented 3% silicon steel by peak flux densities in the range 1.4–1.8 T are predicted by simple formulas. The formulas are based on the increasing sides all having the same shape, and the width of the loop being dependent on the increment below the peak and independent of actual peak value. Agreements of a few percent with published loops are possible. Minor loops are also predicted and modified to give sensible results when the minor loop almost returns to the main-loop peak. Agreement with published data is not as good for minor loops.

DOI:10.1049/ij-epa.1978.0011

出版商:IEE    

年代:1978

数据来源: IET