Calculation of stray load losses

Abstract

Early in the history of the development of the alternating current (AC) generator it was recognized that there might be losses present under load conditions in addition to the no-load losses and the armature copper loss due to load current. Because no one had a satisfactory means of measuring this loss it was not included in the early definitions of conventional efficiency. In 1913 papers were presented giving the results of carefully made input - output tests which tended to show that the entire loss on sustained polyphase short circuit should be taken as a measure of the stray load loss for the salient pole alternator. This rule has remained in force and in view of its general acceptance it is to the interest of designers of salient pole alternators to be able to predetermine this loss. It is the purpose of thispaper to present some general methods of attacking the problem. It is not intended that the results should be complete but they are presented simply as a starting point for the attack on this problem. Instead of trying to develop a single formula for the short circuit core loss, it is desirable to separate the total loss into distinct parts and develop. formulas for each of these parts separately. The parts into which it is most conveniently divided are: 1. An eddy current loss in the armature copper. 2. A loss in the stator iron. 3. A pole face loss. 4. An end loss. 5. A loss in the amortisseur winding. These component parts will be discussed in turn.