The 60- and 400-Hz properties of a pressed compact are compared to Epstein pack tests of a typical cold-rolled motor lamination (CRML) steel and an M-19-grade silicon steel, shown in Figs. 2.60 and 2.61, respectively.
At the typical ASTM-designated test induction of 15 kG and 60 Hz, the core loss of the pressed test core is significantly poorer than that of the M-19 and slightly poorer than that of the CRML steel (see Fig. 2.60). However, in the high-induction range of greater than 18 kG, where many motors operate, the pressed core exhibits a lower core loss than the CRML. At 400 Hz (Fig. 2.61), the loss behavior of the pressed core is significantly better than that of the CRML and very similar to that of the M-19 over the entire induction range. The core loss of the pressed core exhibits a lower dependence with the frequency than the M-19 silicon steel. The difference in the core loss as a function of frequency is thought to be related to the different loss components that constitute the core loss.
FIGURE 2.60 Core loss at 60 Hz.
FIGURE 2.61 Core loss at 400 Hz.
To understand the loss mechanism more completely, one can measure the losses as a function of frequency and express them in a classical manner, as shown in Eq.
(2.32).
Note that for the pressed core only about 5 percent of the total core loss at 60 Hz is due to eddy current loss. The remaining 95 percent is hysteresis loss. A typical lamination steel will exhibit a 50/50 eddy current/hysteresis ratio at 60 Hz.
Figure 2.63 shows the total core loss of the pressed material at 60 Hz, separated into hysteresis loss and eddy current loss components (the eddy current loss comprises the classic eddy current loss and anomalous loss.) Over the entire induction range, the eddy current losses are a very small part of the total losses.
The relatively small eddy current losses keep the total losses low at higher frequencies. Figure 2.64 shows the comparison of the loss per cycle, measured at 15 kG, of the pressed material to a CRML steel and a nonoriented silicon steel, M-19. In both comparisons the hysteresis loss of the pressed material is greater, but the eddy current loss is less. At low frequencies the pressed material has the highest core loss. At around 60 Hz the pressed material losses are comparable to the CRML steel losses and are much lower at higher frequencies. The M-19 steel has the lowest core
FIGURE 2.62 Eddy current and hysteresis loss versus frequency, Hz.
loss at the lower frequencies. Yet at around 400 Hz the core loss for the pressed material is comparable to that of the M-19 steel. The pressed material has the lowest loss at frequencies greater than 400 Hz.
The lower total core loss for the pressed material is obviously due to the lower eddy current losses. Figures 2.65 and 2.66 show the percentage of eddy current loss for each of the materials at 60 and 400 Hz, respectively. At both frequencies the per-
FIGURE 2.63 Core loss components at 60 Hz.
FIGURE 2.64 Comparison core loss versus frequency.
centage of the total core loss due to eddy current losses is the lowest for the pressed material. The low eddy current loss for this
pressed material makes it a good candidate for motors.