In most motor design where optimum efficiency is not the major criterion, the induction level in many portions of the motor stator is significantly greater than 18 kG.
FIGURE 2.65 Percent eddy current loss at 60 Hz.
FIGURE 2.66 Percent eddy current loss at 40 Hz.
Additionally, the waveform of the induction in most motors is rich in harmonics. Thus, the core loss in the motor is not the core loss guaranteed by the steel manufacturer at 15 kG and under sinusoidal flux conditions, but is higher due to the higher operating induction and harmonics in the induction waveform.
In the case of electronically controlled motors, the imposed voltage is not normally sinusoidal but is a square wave, as shown in Fig. 2.67. As a result, the flux density is very nonsinusoidal.
FIGURE 2.67 Electronically commutated motor waveform.
A Fourier analysis of this nonsinusoidal waveform is shown in Fig. 2.68. The core loss under these magnetizing conditions could be expressed as shown in Eq. (2.34):
where the total core loss Pc will be higher than the core loss measured under sinusoidal flux conditions. One might anticipate that a material exhibiting a low eddy current loss component might enhance the performance of these types of motors.
FIGURE 2.68 Fourier analysis of waveform.