Q. The N-coil windings of a three-phase, two-pole machine are supplied with currents ia,ib, and ic, which producemmfs given by Fa = Nia cos θm; Fb = Nib cos(θm - 120°); and Fc = Nic cos(θ - 240°), respectively.
(a) If the three-phase windings are connected in series and supplied by a single-phase voltage source, find the resultant mmf due to all the three windings as a function of θm.
(b) If the three-phase windings are connected to a balanced three-phase voltage supply of f Hz (with positive sequence), determine the resultant mmf.
(c) Letting θm = ωmt + α, obtain the relationship between ωm and ω(= 2πf ) that results in maximum mmf.