No-Load Copper Eddy-Current Losses

One of the factors which is sometimes responsible for very considerable losses in rotating machines is that of eddy-current losses in the copper conductors resulting from slot leakage flux produced by the main flux. These losses occur at no-load as well as under load and should not be confused with the copper losses resulting from the slot leakage flux produced by the load current. These no-load copper losses occur in salient pole machines, both d-c. and a-c., and in induction motors. This paper is an attempt to remove the calculation of no-load copper eddy-losses from the field of empiricism where it has previously been and to place it on a firm theoretical foundation. Test results are presented which show that the theoretical formulas which have been developed are correct. Some of the consequences of this analysis are rather unexpected where the frequencies are sufficiently high to produce large skin effect. For instance, laminating the copper may produce increased or decreased losses, depending upon the conditions.