d.c. source
armature input
motor input
supply lines
Answer is Right!
Answer is Wrong!
Detailed SolutionThe rotor copper losses, in a synchronous motor, are met by
Synchronous motors
82. While starting a synchronous motor by induction motor action, field winding is usually
connected to D.C. supply
short-circuited by low resistance
supply B. short-circuited by low resistance C. kept open-circuited
none of the above
Answer is Right!
Answer is Wrong!
83. The back e.m.f. in the stator of a synchronous motor depends on
number of poles
flux density
rotor speed
rotor excitation
Answer is Right!
Answer is Wrong!
Detailed SolutionThe back e.m.f. in the stator of a synchronous motor depends on
84. A synchronous motor can develop synchronous torque
when under loaded
while over-excited
only at synchronous speed
below or above synchronous speed
Answer is Right!
Answer is Wrong!
Detailed SolutionA synchronous motor can develop synchronous torque
85. The efficiency of a properly designed synchronous motor will usually fall in range
60 to 70%
75 to 80%
85 to 95%
99 to 99.5%
Answer is Right!
Answer is Wrong!
Detailed SolutionThe efficiency of a properly designed synchronous motor will usually fall in range
86. Synchronous motors are generally not self-starting because
the direction of rotation is not fixed
the direction of instantaneous torque reverses after half cycle
startes cannot be used on these machines
starting winding is not provided on the machines
Answer is Right!
Answer is Wrong!
Detailed SolutionSynchronous motors are generally not self-starting because
87. In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
supplied with unbalanced voltage
under-loaded
over-loaded
none of the above
Answer is Right!
Answer is Wrong!
88. When a 3-phase synchronous generator is supplying a zero power factor lagging load, the armature field affects the main field in the following way
augments it directly
directly opposes it
cross-magnetises it
none of the above
Answer is Right!
Answer is Wrong!
89. The power developed by a synchronous motor will be maximum when the load angle is
zero
45°
90°
120°
Answer is Right!
Answer is Wrong!
Detailed SolutionThe power developed by a synchronous motor will be maximum when the load angle is
90. To limit the operating temperature an electrical machine should have proper
voltage rating
current rating
power factor
speed
Answer is Right!
Answer is Wrong!
Detailed SolutionTo limit the operating temperature an electrical machine should have proper