The M. M. F. wave of polyphase windings: With special reference to sub-synchronous harmonics

The m. m. f. waves of fractional slot windings or other irregular windings are found to contain harmonic components having wavelengths greater than two pole pitches. These are designated as sub-synchronous harmonics since their harmonic order is lower than that of the synchronously rotating wave. They induce currents in the damper windings of synchronous machines which may produce noticeable loss. Some test data concerning losses are included. These harmonics have an effect upon reactance and, under certain conditions, they may cause vibration. An appendix covers the calculation of the m. m. f. of three-phase fractional slot machines.