Motor Results (Electric Motors)

2.5.6
Two example four-pole brushless stator cores were made from pressed particles and built into motors. One motor operated in the 400-Hz range, while the second operated in the 700-Hz range. Both motors were compared to identical motors in which the stator cores were made from punched 24-mil-thick M-19 silicon steel lamina-tions.The data are presented in Table 2.5.

TABLE 2.5 Performance of Pressed Core Compared to Standard Laminated and Stacked Core

	Torque, Current, Speed, Efficiency, oz ■ in. A r/min %	Temp. rise, C°
(a) Low-speed, four-pole brushless motor
Standard Pressed	4.0 4.6 11,401 67.2 4.1 4.4 11,662 69.4	14.0 12.6
(b) High-speed, four-pole brushless motor
Standard Pressed	9.4 7.1 15,746 64.5 9.4 6.6 16,881 74.5	49.4 27.8

In the case of the motor operating in the 400-Hz frequency range, Table 2.5a, the torque was held constant at approximately 4.0 oz • in, and the performance was measured. The pressed core performed statistically better than the laminated core. This is attributed to the fact that, although the core loss of the pressed core is comparable to the M-19 silicon steel in the 400-Hz frequency range (Fig. 2.64), the loss associated with the higher-frequency harmonics imposed on the core by the power supply benefits from the lower eddy current losses exhibited by the pressed core (Fig. 2.66).
In the case of the motor operating in the 700-Hz frequency range, the torque was held constant at approximately 9.4 oz • in, and the performance measured. In this case the pressed core outperformed the standard M-19 silicon steel laminated core (Table 2.5&). It had a lower current draw, ran at a higher speed, and had a lower temperature rise. Overall, the efficiency of the pressed core was greater by 10 percentage points. This motor performance is obviously the result of the much lower core losses of the pressed material in the 700-Hz frequency range (Fig. 2.64).