Analysis by two reaction theory
Analysis by two reaction theory:
The effects of salient poles can be taken into account by resolving the armature current into two components; Id perpendicular to excitation voltage E0 and Ia along E0 as shown in phasor diagram in Fig. (1). Note that this diagram is drawn for an unsaturated salient-pole generator operating at a lagging power factor cos Φ. With each of the component currents Id and Iq , there is associated a component synchronous reactance Xd and Xq respectively.
Xd = direct axis synchronous reactance
Xq = quadrature axis synchronous reactance
If X1 is the armature leakage reactance and is assumed to be constant for direct and quadrature-axis currents, then,
Xd = Xad Xl ; Xq = Xaq Xl
Note that in drawing the phasor diagram, the armature resistance Ra is neglected since it is quite small. Further, all values arc phase values. Here V is the terminal voltage phase and E0 is the e.m.f. per phase to which the generator is excited.
Referring to Fig. (1).