Electrical Machines( Synchronous Machines ) :
Q-216. In a synchronous
generator, one pole is responsible for
a. 90 degree electrical of induced emf
b. 180
degree electrical of induced emf
c. 360
degree electrical of induced emf
d. 720
degree electrical of induced emf
Q-217. If the rotor poles of a 6
pole synchronous generator shift by 8 mechanical degrees from no load to full
load, then its torque angle will be
a. 12 degrees
b. 24
degrees
c. 48
degrees
d. 136
degrees
Q-218. If coil side in one slot
is connected to a coil side in another slot which is one pole pitch distance
away from first slot, the winding is said to be
a. Short pitched
b. Full
pitched
c. Concentrated
d. Distributed
Q-219. Among the following
sentences which is/are true about short pitch coils
a. Less amount of copper is required
b. Eliminates
high frequency harmonics
c. Minimizes
eddy current and hysteresis losses
d. All
of the above
Q-220. In practice, which
combination of armature winding is preferred for the alternators?
a. Single layer, full pitched and concentrated type
b. Single
layer, short pitched and distributed type
c. Double
layer, full pitched and concentrated type
d. Double
layer, short pitched and distributed type
Q-221. Due to short pitching,
the induced emf gets
a. Reduced
b. Increased
c. Remains
same
d. None
of these
Q- 222. In a 4 pole, 3
phase alternator, armature has 40 slots. It is using an armature winding which
is short pitched by one slot. Its coil span factor is
a. 0.9
b. 0.9243
c. 0.9476
d. 0.9876
Q- 223. The factor by which
there is reduction in the emf due to distribution of coils is called
distribution factor. It is given by
a. sin (β / 2m) / msin(β / 2)
b. sin(β
/ m) / msin(mβ / 2)
c. sin(m
β/2) / msin(β / 2)
d. msin(β
/ 2) / sin(m β / 2)
Q- 224. The generalized
expression for emf equation of an alternator is
a. Eph = 4.44f φ Tph
b. Eph =
4.44 KcKdf φ E
c. Eph =
4.44 KcKdfφTph
d. Eph =4
KcKdf φ Tph
Q- 225. For a short pitch
and distributed winding, the value of coil span factor and distributed factor
a. Both are less than unity
b. Less
than unity, greater than unity
c. Greater
then unity, less than unity
d. Both
are greater than unity
Q- 226. An armature of a
three phase, 8 pole alternators has 120 slots. The distribution factor is equal
to
a. 0.897
b. 0.946
c. 0.957
d. 1.
Q- 227. A 3 phase, 50 Hz, 8 pole,
star connected alternator has 120 slots having 10 conductors per slot. The flux
per pole is 0.02 Wb and distributed sinusoidally. The induced emf per phase for
full pitch winding is
a. 849.816 V
b. 956.782 V
c. 1046.812
V
d. None
of these
Q- 228. For reducing the slot
harmonics in an alternator, the length of air gap is
a. Reduced
b. Increased
c. Not
related to harmonics
d. None
of these
Q- 229. To minimize the harmonics
from the voltage waveform, the suitable steps is / are
a. Using distributed type of
winding instead of concentrated type
b. Using
fractional slot windings
c. Skewing
the pole face
d. All
of these
e. None of these
Q- 230. If x is the order of
harmonic component, then the general expression for distribution factor is
a. xsin(β / 2m) / msin(β / 2x)
b. sin(x
β /m) / xmsin(m β / 2)
c. sin(xm
β / 2) / msin (x β / 2)
d. xmsin(β
/ 2) /sin(mx β)
Q- 231. Generally the effective
resistance of alternator under a.c. condition is taken as
a. Less than 1.25 times the d.c.
resistance
b. 1.25
to 1.75 times the d.c. resistance
c. Greater
than 1.75 times the d.c. resistance
d. None
of these
Q- 232. Salient pole alternators
are best suitable for the application of
a. Hydro electric power plant
b. Thermal power plant
c. Tidal
power plant
d. Nuclear
power plant
Q- 233. When the voltage
across any two terminals of an armature winding of star connected alternator,
then the armature resistance per phase is
a. Half of the resistance
observed across any two line terminals
b. 3/2 of the
resistance observed across any two line terminals
c. 2/3
of the resistance observed across any two line terminals
d. Same
as the resistance observed across any two line terminals
Q- 234. In the given figure of
delta connected alternator, armature resistance per phase (Ra) is equal to
a. 1/2 of RRY
b. 2/3
of RRY
c. 3/2
of RRY
d. RRY
Q- 235. The leakage flux in
the armature of alternator makes the armature winding
a. Inductive in nature
b. Capacitive in
nature
c. Resistive
in nature
d. All
of these
Q- 236. Out of two alternators
which are sharing an inductive load equally, if excitation of one alternator is
increased then
a. Other alternator will
deliver less current
b. Other alternator
will deliver more current
c. Both
will deliver equal current
d. None
of these
Q- 237. The
effect of armature flux in an alternator depends on
a. Magnitude of current flowing through the
armature winding
b. Nature
of power factor of the load connected to the alternator
c. Both
(a) and (b)
d. None
of these
Q- 238. If ∅f is
the main flux produced by the field winding of alternator is responsible for
producing Eph, then
a. Eph leads ∅f by
90 degree
b. Eph leads
∅f by
45 degree
c. Eph lags
∅f by
45 degree
d. Eph lags
∅f by
90 degree
Q- 239. If the
load connected to the alternator are having zero leading power factor and zero
lagging power factor, then the nature of load in each case will be
a. Inductive, capacitive
b. Inductive,
inductive
c. Capacitive,
capacitive
d. Capacitive,
inductive
Q- 240. The
synchronous reactance of an alternator is equal to
a. Leakage reactance of armature
b. Armature
reaction reactance
c. Sum
of leakage reactance and armature reaction reactance
d. Difference
of leakage reactance and armature reaction reactance
Q- 241. Consider
a purely inductive load connected to the alternator having zero lagging power
factor. In this case the effect of armature reaction will be
a. Demagnetizing effect
b. Cross
magnetizing effect
c. Both
(a) and (b)
d. None
of these
Q- 242. When
a purely capacitive load is connected to the alternator having zero leading
power factor then the armature flux and main flux will be
a. In the same direction
b. In
the opposite direction
c. Main
flux will lead armature flux by 90 degree
d. Main
flux will lag armature flux by 90 degree
Q- 243. The
open circuit voltage and short circuit current of a 3 phase, star connected
alternator are 1050 V and 250 A respectively. Its field current is 12 A. Then
the synchronous impedance of alternator will be
a. 1.34 ohm
b. 1.69
ohm
c. 2.42
ohm
d. 2.85
ohm
Q- 244. A 6
kVA, 220 v 3 phase, star connected synchronous generator has a winding
resistance of 0.15 ohm per phase and synchronous reactance of 6.1 ohm per
phase. The voltage regulation of alternator at a load power factor of 0.8
lagging will be
a. 58.10 %
b. 68.43
%
c. 69.02
%
d. 72.81
%
Q- 245. If
two mechanically coupled alternators deliver power at 50 Hz and 60 Hz
respectively, then the highest speed of alternators will be
a. 1200 rpm
b. 1500
rpm
c. 600
rpm
d. 300
rpm
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