Predetermination of generated voltage in heteropolar inductor alternators

When the slotted surfaces of the stator and rotor of a heteropolar inductor alternator occupy different relative positions during rotation, several airgap configurations are obtained depending on the stator/rotor slot ratio and the toothwidth/slot-pitch ratios in both stator and rotor. These configurations are classified in seven basic positions and are analysed by conformal mapping to give expressions for specific permeance at different instants of travel of the rotor. The results are used to determine the steady-state flux linkages and induced voltages in the a.c. phase coils. A simpler analysis of the airgap permeance is also given neglecting fringing of flux and classifying the airgap configurations into four basic positions. This leads to analytical expressions for the generated voltage. Two inductor alternators were constructed with different slot ratios and coil pitches, and the oscillograms of their generated voltages are compared with predicted waveforms.