Surface iron losses with reference to laminated materials

Surfaces or pole-face losses are assumed to be governed by ten factors and the influence of each on the resulting losses is considered. After reviewing the work of the previous investigators an account is given of some rather extensive tests recently completed by the writers. These tests cover results obtained on an experimental salient pole machine and an experimental 3-phase induction motor. Data are given for various types and thicknesses of commercial sheet. For a given material and machine the surface losses are assumed to be a function of the air-gap induction, ratio of slot width to single air gap, tooth frequency and slot pitch or width. The laws of variation of surface losses with respect to these variables are determined from experimental results and are shown to be in general exponential. The relation between hysteresis and eddy-current losses and the effect of variations in thickness and resistivity of laminations is considered in some detail. Simple methods are given for applying these results to actual design problems which involve plotting the various functions on double log paper, a slide rule being then sufficient for all calculations. The appendix gives a description of a graphical method of separating the various types of core losses which exist in a polyphase induction motor.