09‐Dec‐14
46
A 3-phase, wye-connected, round-rotor synchronous
generator rated at 10 kVA, 230 V has a synchronous
reactance of 1.2 Ω per phase and an armature
resistance of 0.5 Ω per phase. Calculate the percent
voltage regulation at full-load with 0.8 lagging
power factor.
47
1
09‐Dec‐14
 The
phasor diagram is shown in Figure from
which:
48
 Substituting:
 We
get:
 Then
49
2
09‐Dec‐14
 Repeat
the previous problem for the case of 0.8
leading power factor, other data remaining
unchanged.
50
 Notice:

The voltage regulation at full-load with 0.8 leading
power factor is negative
51
3
09‐Dec‐14
 For
the generator of example (2), determine the
power factor such that the voltage regulation is
zero on full-load.
52
53
4
09‐Dec‐14
 A 3-phase,
round-rotor synchronous generator is
rated 150 MW, 0.85 power factor, 12.6 kV, 60 Hz,
and 1800 rpm. Each winding has a line-to-neutral
resistance of 1.535 Ω. The data for the no-load
magnetization curve are:
 The
short-circuit armature-current test gives a
straight line through the origin and through rated
armature current at 700-A field current.
54
a)
b)
c)
d)
Determine the unsaturated synchronous
impedance per phase.
Determine the saturated synchronous impedance
per phase.
Draw a phasor diagram and determine the
voltage regulation for the condition of rated load
and 0.85 power factor lagging.
Repeat part (c) for rated load and 0.85 pf leading.
55
5
09‐Dec‐14
 The
saturation curve and the short-circuit test data
are plotted
56
 Calculate
 From
the rated current:
Fig.:
ab-
57
6
09‐Dec‐14
 =cos-1
0.85 = -31.8°. The phasor diagram is
shown in Fig
58
 For
 = +31.8°, Fig. (b) gives the phasor diagram.
59
7
09‐Dec‐14
 A 3600
rpm, 60 Hz, 13.8 kV synchronous
generator has a synchronous reactance of 20Ω. The
generator is operating at rated voltage and speed
with the per phase excitation voltage Ef=11.5kV
and the torque angle δ=15°
 Calculate (a) stator current, (b) power factor, and
(c) total output power.
60
 a)
 b)
 c)
61
8
09‐Dec‐14
 For
the synchronous generator of example (5),
determine (a) the maximum power that can be
converted from mechanical to electrical form
without loss of synchronism if the field current is
unchanged and (b) the value of current Is for this
condition
62
 a)
Since δ=90°:
 b)
63
9