The following is a paper by H. Aspden published by the Institution of
Electrical Engineers as Monograph No. 165M (January 1956) and later in Proc.
I.E.E. vol. 103C at pp. 272-278 (1956).
MAGNETIC TIME-LAG EFFECTS IN SOLID STEEL CORES
discrepancy between the theoretical eddy-current effects and the actual
eddy-current effects in thick steel cores is investigated. By using thick cores
the magnetic inhomogeneity arising from ferromagnetic domain configuration is of
little consequence and the discrepancy may be attributed to an intrinsic
time-lag effect in the magnetization process. The time-lag is measured and
explained in terms of a localized eddy-current action associated with the
dissipation of hysteresis loss. It was found that the time-lag depended upon
frequency and was less important at high frequencies.
The experimental research reported in this paper aimed at explaining the
mysterious extra loss that occurs in steel when subjected to alternating
magnetization. This particular paper concerned the problem in solid steel rods
magnetized at kilocycle frequencies as distinct from that in laminated steels at
power frequencies. One important distinction between these two cases is that the
physical size of magnetic domains and consequent magnetic inhomoheneity should
be of lesser relevance in the magnetization of solid cores, thereby allowing one
to see if the eddy-current loss anomaly could be eliminated in the latter
situation and confined to the sheet steel laminations where magnetic domain
inhomogeneity is prevalent.
In the event it was found that in the solid
steel cores there is indeed an anomalous loss resembling an eddy-current effect,
but it is attributable to what one might term the dynamic component of the
hysteresis loss. It corresponds to a time-lag effect of the order of 10
microseconds and arises from the increase in magnetizing field during the period
taken by the jumps in the movement of the magnetic domain walls. However, this
degree of time-lag cannot explain the eddy-current loss anomaly that occurs at
the lower power frequency of 50 Hz, where time-lags of the order of 100
microseconds and more are needed to match the eddy-current loss
Accordingly, this paper, though establishing a case for added
loss attributable to magnetic time-lag effects has to be considered in the
context of the separate reports which were based on the same Ph.D. research
for further information.