The effect of temperature upon the hysteresis loss in sheet steel

In the paper which the writer presented before the Institute last year upon this subject^∗ it was shown that there was no apparent change in the law governing the variation of the hysteresis loss with the induction for all temperatures from atmospheric up to near the point where the steel became non-magnetic. The writer suggested at that time that the rate of heating the sample might affect the change in hysteresis loss with changing temperature and the measurements described below were carried out to investigate this point. It was thought also that some additional light might be thrown on this subject if hysteresis loops were obtained from the sample near the non-magnetic temperature. This had not been done in the previous tests as the samples had been prepared for the two-frequency method of measurement in order to obtain results quickly at any temperature over as wide a range of induction as possible. An attempt was made at that time to obtain a few characteristic loops at high temperatures, but the use of iron wire for the secondary winding on the sample introduced errors on account of variable thermal currents in the galvanometer circuit which could not be readily eliminated. It was also found that the insulation resistance between primary and secondary at high temperatures was hot sufficiently good to permit measurements by the galvanometer method, although no error could be detected from this source with the two-frequency wattmeter method.