The Effect of Displaced Magnetic Pulsations on the Hysteresis Loss of Sheet Steel

Most modern revolving electrical apparatus has teeth on the rotor or stator, or both, which are subjected to constantly varying reluctance. This variation of reluctance causes high-frequency changes of flux superimposed on the working flux. The result is a series of displaced hysteresis loops. This investigation was undertaken to determine the magnitude and, if possible, some of the laws governing the change in hysteresis loss due to displacing a loop from its symmetrical position. An account is given of some early tests which, within the limits of induction studied, resulted in certain definite conclusions. It is pointed out that the data from these displaced hysteresis loops limit the applicability of the Steinmetz hysteresis formula to symmetrical loops. Recent tests are then described, giving the details of a new apparatus for obtaining hysteresis loops and showing an improved method of making displaced a-c. watt-loss tests. Numerous loops and curves are included, showing the effect of displacement on the shape and area of the hysteresis loop. No definite laws could be formulated from the data, but some general conclusions are given.