Airgap and stator flux distribution in Guy-type medium-frequency inductor generators

The first part of this paper is concerned with no-load permeance variations and overall flux distribution in the airgap of Guy-type inductor alternators. Teledeltos models were used to predict the permeance variation over a rotor pitch and over a whole stator main tooth for a complete cycle. The flux utilisation coefficient calculated from the permeance variation across a whole main tooth gave a better prediction of the open-circuit curve than when a rotor slot pitch was considered. Teledeltos models were also constructed to investigate how the depth of slot and the slope of side of the slots affects the flux utilisation coefficient. A simple approximation to the airgap permeance allows the airgap-permeance variation and the flux utilisation coefficient to be calculated for any tooth-slot geometry for 3 kHz machines. Detailed flux distribution in the airgap region was also predicted from Teledeltos plots. The asymmetry that exists between the two main teeth over a d.c. pole pitch causes flux variations to link the field winding, resulting in high voltages across individual field coils unless suitable damping windings are used. The second part considers in detail the open-circuit and load flux distribution in the siriall stator teeth of Guy-type inductor alternators. Although the flux variation across the total tooth surface is approximately sinusoidal, a considerable amount of harmonic flux is present in small sections of the surface. Under load conditions, an additional m.m.f. due to armature reaction acts on the airgap permeance, resulting in a nonuniform distribution of flux across the tooth surface; from these flux waveforms, it is possible to calculate the losses in the stator teeth with a greater degree of accuracy than was previously achieved. A companion paper (see p. 387) discusses rotor flux distribution in Guy-type medium-frequency inductor alternators.