ANALYSES OF SQUIRREL-CAGE WINDINGS WITH PARTICURLAR REFERENCE TO THE DEVELOPMENT OF A HIGHTLY STABLE RELUCTANCE MACHINE
Abo-Shady, Sirag El-Dean El_Sayed
Reluctance machines have been very successfully used in a wide variety of applications where their special features have made them a natural or even an inevitable choice. For the last few years, a number of investigators have been engaged in improving the overall performance of such machines. This has been achieved by adopting several rotor configurations which are different from the conventional reluctance rotor. In order to justify the choice of conventional reluctance machines for the studies presented in the thesis, a general survey of various types of reluctance machines is presented. One of the main objectives of the thesis is to show that the performance is a conventional reluctance machine can be enhanced to a great extent by changing the distribution of the rotor bars. A simple and realistic method of analysis of developed for investigating the effects of the distribution of the rotor bars on the asynchronous, the dynamic stability and the transient behavior of conventional reluctance machines. The method enables a design engineer to obtain the most suitable arrangement o the rotor vars at the design stage. In light of the asynchronous, the transient and the stability performance of a specific machine, two suitable arrangements are recommended for the rotor bars. These arrangements are characterized by the outstanding features of minimum amplitude of the pulsating torque, smooth torque-slip characteristics, stable operation at all frequencies, moments of inertia and operating loads and better capability of pulling-into-synchronism. A considerable part of the thesis is devoted to the studies related to the consideration of the phenomenon of skin-affect during the transient operation of electrical machines. The general partial differential equations of the magnetic vector potential is derived on the basis of two-dimensional analysis. With the help of the principles of finite-difference method, numerical techniques are presented for solving the field equations obtained from both two- and single-dimensional analyses. The techniques are used for investigating the transient skin-affect of a deep bar embedded in a slot. They analysis and the accuracy of the technique developed are verified through comparisons between numerical and analytical results. Incorporating the skin-effect on the transient analysis of electrical machines necessitates the development of a novel approach for the analysis of squirrel-cage windings. This involves the derivation of voltage an torque equations based on a new choice of the rotor circuits of a reluctance machine. The rotor voltage equations are formulated in such a way that the transient skin-effect can be easily incorporated in the analysis. A sound per-unit system is also presented. The application of the novel approach is demonstrated by considering a reluctance machine having four bars per pole. Further, the transient performance of a machine having one of the two recommended designs is investigated with and without the consideration of the skin-effect of bars and ending segments. Although the analyses presented in the thesis are devoted to the case of reluctance machines, their main features can be applied to synchronous machines as well as to induction machines having integral numbers of bars per pole.