High-Frequency Iron Losses in Fractional-Horsepower Induction Motors

A comparison between experimental and theoretical values for exponents a, b, and c is made in Table IV. The experimental and theoretical values for exponents a and b are essentially the same. The experimental value for exponent c agrees favorably with the theoretical value for large air gaps but is low for small air gaps. This result is probably due to the many simplifying assumptions that were made in the derivation of PR, including the correction for fringing. Also, the airgap flux pulsation, B, is more nearly asine wave for large air gaps than for small air gaps. The theoretical values for the exponents were determined as indicated previously by assuming that the eddy-current and hysteresis loss components of the highfrequency loss each contributed equally to the total high-frequency loss. The results which were described in the previous section for rotor 8 justify this assumption. On the basis of this study, a practical design formula for small 3-phase induction motors is Phf = KBm2.1ft1.5(PR/g)¿¿¿D2W (46) The coefficient, K, is 1.36×10¿7 for rotor laminations made from low-carbon steel and for the particular manufacturing processes that were employed to build the rotors associated with this study. Equation 46 will also give sufficiently accurate design results for small singlephase induction motors because the calculated results will be slightly high, or on the conservative side. Equation 46 is not radically different from equation 3 which is Adams´1 semiempirical formula for rotor surface loss.