The teaching of the principles of electrical machine design

Abstract

The principles of electrical design as taught in colleges and textbooks do not completely coincide with the principles used in design offices in industry. It is the intention of this, paper to indicate how such teaching can with advantage be modified and amplified so as to be of greater service to those entering industry. The causes leading to the differences are considered, and the difficulties experienced by college students on their first entry to a design office are analysed. The general considerations which should affect the arrangement of a design course are discussed, such as logical sequence, mathematical outlook and the effect of practical considerations. The necessity for students to have a full knowledge of the theory of electrical machines prior to undertaking a course on design is stressed. The more important subjects dealt with in a design course are treated individually, and the underlying principles discussed. Considerable attention is devoted to the need for a full understanding of the nature of the physical phenomena concerned. In particular, armature reaction and leakage reactance and their physical background are discussed in detail. Fallacies in theory, and the corresponding mis-statements which appear in many textbooks with regard to iron loss and the leakage reactance of end-windings, are exposed, and more accurate information is put forward. Particulars suitable for inclusion in a design course are included with regard to unbalanced magnetic pull, stray loss, and the crawling of induction motors. Recommended methods of calculation are given, together with constants determined from experience, and the paper concludes with a table of loading figures and temperature-rise formulae which it is hoped will be of service to teachers.