The relative proportions of copper and iron in alternators

Many radical changes have accompanied the rapid development of alternating-current generators. In the early days, when alternators were designed by rule-of-thumb methods, the relative proportion of copper to iron was high. These machines had very poor inherent regulation, and in many cases failed to give the voltage for which they were designed. These “copper machines” were relatively light, and were considerably cheaper than the “iron machines” which succeeded them. The iron machines, though much heavier and more expensive than their predecessors, had much better regulation. Following this, the characteristics of alternators were more carefully studied so that the designer was able to reduce the weight and again approach the copper machine. Competition between the various manufacturing companies made it necessary for their engineers to design cheaper machines, resulting in a compromise between the “copper” and “iron” machines. We are now at this period, and the designer is to-day confronted with the question: what shall be the relative proportions of copper and iron in this machine? Doubtless the answer is, so to proportion the iron and copper as to obtain the cheapest possible machine.