Iron Losses in Direct-Current Machines

The term iron loss, as used in connection with rotating machinery, is shown to cover a large number of losses, some of which actually do not lie in the iron itself. The term core loss should be used except when the losses are actually located in the iron itself. It is shown that no great accuracy is practicable in the calculation of the actual iron losses, except in special instances, due to the fact that the ordinary treatment of materials in manufacture is such that large discrepancies are almost sure to occur, in certain types of apparatus. A brief explanation of several causes of variation in losses is given. In the treatment of core losses in direct-current machines, the four principal sources of losses are considered, namely-armature ring loss, armature tooth loss, eddy currents in buried condtuctors, and pole face losses. Under eddy current losses is given an explanation of certain losses not usually taken into account, and a crude method of calculation is given, with some tabulated results. Under pole face losses an empirical formula is given, also some tabulated results. The effect of load on losses is discussed, but no calculated results are given. Some of the effects of flux distortion on the losses are shown. A principal object of the paper is to show the impracticability of calculating all the core losses with any great accuracy at noload, and the still greater difficulty in predetermining them with load.