91. In a synchronous machine in case the axis of
field flux is in line with the armature flux, then
the machine is working as synchronous motor
the machine is working as synchronous
the machine is said to be floating
the machine will vibrate violently.
92. If other factors remain constant, the speed
of a synchronous motor in its operating (and load) range is correctly described
by which of the following ?
The speed varies directly only in proportion
to the number of its poles
The speed is independent of the frequency of
the voltage supply
The speed depends on the frequency of the
voltage supply and the number of its poles
The speed depends on the magnitude of the
voltage supply and the number of
93. The induced emf in a synchronous motor
working on leading pf will be
to the supply voltage
than the supply voltage
than the supply voltage.
94. A synchronous machine with low value of
short-circuit ratio has
(A) good speed regulation
95. While starting a synchronous motor by
induction motor action, very high emf is induced in the field. This induced emf
may damage the insulation of the field winding and of slip rings. The insulation
damage can φ be prevented by
the field winding by field discharge resistance
the field winding into several sections
either of (A) or (B) above
of the above.
96. Synchronous motors, arc generally of
pole type machines
pole type machines
97. In which of the following motor the stator
and rotor magnetic fields rotate at the same speed
98. Higher the applied voltage ……………….. will be
the stator flux and ………………. will be the pull
(A) lower, greater
(B) greater, lower
(C) greater, greater
(D) lower, lower.
Questions 99 to 101 refer
to data given below:
An industrial plant has a load of 1500 kVA at an average power factor of
99. Neglecting all losses, the kVA input to a
synchronous condenser for an overall power factor of unity will be
(A) 300 kVA
(C) 600 kVA
(D) 1200 kVA.
750 kVA synchronous condenser is used to correct the lagging power factor of
the plant. The total kVA of the plant is
overall power factor is
(A) 0.895 lagging
(B) 0.75 lagging
(C) 0.75 leading
the load is applied on a synchronous motor, its speed does not fall. The load
is now supplied by
in back emf
in supply voltage
stator magnetic field
taking new angular position slightly back of its no load position.
maximum power developed in a synchronous motor depends on all of the following
value of coupling angle.
a synchronous motor, on a fixed excitation when the load is doubled, the torque
angle φr will become
(A) 2 φr
(B) √2 φr
a synchronous motor, the armature current has the highest value when excitation
(D) high and low.