Two-reaction phasor diagram of a salient-pole synchronous generator is considered, where
I_a = armature current per phase,
X₁ = armature leakage reactance per phase,
X_d = direct axis synchronous reactance,
X_q = quadrature-axis synchronous reactance, and
V = generator terminal voltage, taken as reference.
The voltage in-phase with the direct-axis will be phasor-sum of