136. Zero power factor method of an alternator is used to find its
(A) field resistance
(B) armature resistance
137. The power factor
of an alternator is obtained from its
none of the above.
138. For parallel
operation, alternators must have
(A) same speed
(B) same kVA rating
of the above.
139. For alternation
having fractional pitch of 5/6 the coil span is
140. Fractional pitch
to eliminate 7th harmonic from alternator emf is
141. Consider the
following statements about a three-phase synchronous generator synchronized to
an infinite bus when its mechanical input is increased gradually with field
current held constant:
1. The power factor of
the current supplied becomes more lagging.
2. The power factor of
the current supplied improves.
3. The power factor
4. The load angle is
Of these statements
(A) 1 alone is correct
2 alone is correct
(C) 2 and 4 are
(D) 3 and 4 are
142. A 3-phase
synchronous generator, with its armature resistance and the leakage
being neglected, is synchronized to an infinite bus and its field
is kept constant thereafter. Now the machine is loaded by Supplying
input to the shaft so that the load-angle δ reaches a value of 60°
Under this condition, the operating power-factor would be
(A) 0.866 leading
(C) 0.5 leading
143. A round rotor
synchronous generator has a leakage reactance of 10%, armature reaction
reactance of 90% and negligible armature resistance. With the machine initially
running at rated speed and terminal voltage of 1.0 p.u., a 3-phase
short-circuit is applied. The sustained armature current will be
(A) 1.25 p.u.
(B) 1.11 p.u.
(D) 0.9 p.u.
144. Following a
sudden short-circuit at the terminals of a 3-phase unloaded synchronous
generator, the initial effect of the pole-face damper windings, is to
the armature flux through the direct-axis magnetic circuit of the machine
only partial linkage of the armature flux with the main field winding
the armature flux to completely link the damper winding
the armature flux and confine it to the leakage flux path in the air-gap.
145. In a synchronous
generator operating at zero pf lagging, the effect of armature reaction is
magnetizing and cross-magnetizing.
146. Which of the
following limit the reactive power output of a synchronous generator
1. Armature current
3. Load angle
Select the correct answer
using the codes given below:
(B) 2 and 3
(C) 3 and 4
147. The steady-state
stability limit of a synchronous generator can be increased by
(A) an increase in its reactance
(B) an increase in the excitation of the
(C) a decrease in the moment of inertia of
(D) an increase in the
moment of intertia
of the machine.