Q. Show Effects of Saliency and Saturation?
Because of saliency, the reactancemeasured at the terminals of a salient-pole synchronousmachine as opposed to a cylindrical-rotor machine (with uniform air gap) varies as a function of the rotor position. The effects of saliency are taken into account by the two-reactance theory, in which the armature current ¯I_{a} is resolved into two components: I_{d} in the direct or field axis, and Iq in the quadrature or interpolar axis. I_{q} will be in the time phase with the excitation speed voltage ¯E_{f} , whereas Id will be in time quadrature with ¯E_{f} . Direct- and quadrature-axis reactances (X_{d} and X_{q}) are then introduced to model the machine in two axes. While this involved method of analysis is not pursued here any further, the steady-state power-angle characteristic of a salient- pole synchronous machine (with negligible armature resistance) is shown in Figure. The resulting power has two terms: one due to field excitation and the other due to saliency. The maximum torque that can be developed is somewhat greater because of the contribution due to saliency.