SYNCHRONOUS MOTOR CHARACTERISTICS
(V-curves )
The steady-state characteristics of a synchronous motor represented by
phasor diagrams are shown as function of the excitation voltage E: for low values of E,
the motor is said to be under excited and the current I
lags the terminal voltage V where as,
for large values of E, the motor becomes over
excited with the current now leading the voltage.
Note that the locus of the current phasor is a vertical line meaning that
I cos(φ)
is constant; similarly
the locus of E
is a horizontal line satisfying the condition that E sin(δ) is constant; both constraints are the consequence of maintaining constant power
P = I V cos(φ) = E V sin(δ) / X. The basic phasor equation is
V = E + jX I. The associated V-curve (I versus E) is also
plotted.