The steady-state characteristics of a synchronous motor represented by phasor diagrams are shown as function of the load P with the excitation voltage E kept constant.

The power expression is P = I V cos(φ) = E V sin(δ) / X. The basic phasor equation is V = E + jX I.

The locus of E is a portion of a circle of radius E centered at the origin of the complex plane.

The locus of I is also a circle of radius E/X centered on the imaginary axis at V/X.

The power P versus the torque angle δ is also plotted.