OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
ENGR. FRANCIS NICOLAS ESCOBAR
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
A multipolar machine with cylindrical rotor has a
uniform air-gap, because of which its reactance
remains the same, irrespective of the spatial
position of the rotor. However, a synchronous
machine with salient or projecting poles has nonuniform air-gap due to which its reactance varies
with the rotor position. Consequently, a cylindrical
rotor machine possesses one axis of symmetry
(pole axis or direct axis) whereas salient-pole
machine possesses two axes of geometric
symmetry (i) field poles axis, called direct axis or
d-axis and (ii)axis passing through the center of
the interpolar space, called the quadrature axis or
q-axis.
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
Obviously, two mmfs act on the d-axis of a salient-pole
synchronous machine i.e. field m.m.f. and armature m.m.f.
whereas only one m.m.f., i.e. armature mmf acts on the qaxis, because field mmf has no component in the q-axis. The
magnetic reluctance is low along the poles and high
between the poles. The above facts form the basis of the
two-reaction theory, according to which:
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
EXAMPLE
A 30 kVA, 220 volt, wye connected, 3 phase, salient pole
synchronous generator supplies rated load at 0.707
lagging power factor. The reactance per phase are
Xd = 2Xq = 4 ohms. Determine the percent voltage
regulation and the power developed.
%VR = 224%
Pd = 21.21 kW
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
EXAMPLE
A 100 kVa, 400 volts, wye connected salient pole
synchronous generator runs at full load and 80% power
factor leading. If Xd=2Xq=1.1 ohms per phase and Ra is
negligible, calculate the voltage regulation and the power
developed.
%VR = -26.4%
Pd = 80 kW
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
EXAMPLE
A 3-phase alternator has a direct-axis synchronous
reactance of 0.7 p.u. and a quadrature axis synchronous
reactance of 0.4 p.u. Draw the vector diagram for full-load
0.8 p.f. lagging and obtain therefrom (i) the load angle
and (ii) the no-load per unit voltage.
1.515 pu
OPERATION OF A SALIENT POLE SYNCHRONOUS MACHINE
EXAMPLE
A 3-phase, star-connected, 50-Hz synchronous generator
has direct-axis synchronous reactance of 0.6 p.u. and
quadrature-axis synchronous reactance of 0.45 p.u. The
generator delivers rated kVA at rated voltage. Draw the
phasor diagram at full-load 0.8 p.f. lagging and hence
calculate the open-circuit voltage and voltage regulation.
Resistive drop at full-load is 0.015 p.u.