used in the analysis of electrical machines. The former is used to describe the
position in electrical domain and is denoted by θ e , and the second one de fi nes
thephysicalpositionoftherotorinspaceandisdenotedbyθ m .Itisobvious
that rotating the rotor by a mechanical degree θ m leads to the variation in
electrical signal by an angle pθ m . That is, the relationship between θ e and θ m
θ e = pθ m .
Figure 4.39: Back-EMF induced in the winding (p=1).
Figure 4.40: Back-EMF induced in the winding (p=3).
4.2.7 Armature reaction
In the operation of a motor, besides the excitation fi eld, there exists another
magnetic fi eld induced by the current in the armature winding which affects the
distribution of the airgap fi eld. Assuming this process is linear, the effects of the