If a motor frame is found to be excessively hot, which of the following is not likely the cause?
AExcessive loading
BInadequate internal ventilation
CVery high ambient temperature
DFaulty starter
Electrical Engineering · Question Bank
DC Motors
208 of 285 questions match · page 3 of 11. Answer in your head first, then check the solution.
What will you do if the speed of a dc shunt motor should be increase more than the full load speed?
AIncrease the armature current
BIncrease the field current
CDecrease the field current
DDecrease the armature current.
What is the purpose of a “diverter” in a dc series motor?
ATo control the armature current
BTo control the line current
CTo control the speed
DTo control the losses of the motor
What is the reason why a dc shunt motor does not operate on ac supply?
AIts armature resistance is low
BIts field circuit has high resistance
CIts field circuit has high inductance
DDue to reversal of polarity.
Which of the following dc motors is suitable to drive punch press?
ACumulative compound motors
BDifferential compound motors
CSeries motors
DShunt motors
What type of current is flowing in the armature conductors of a dc motor?
AAlternating current
BDirect current
CA non-sinusoidal current
DA full-wave rectified current
Which one is true about the back emf of a dc motor?
AIt aids the supply voltage
BIt opposes the supply voltage
CIt aids both the field and supply voltages
DIt opposes both the field and supply voltages
If the polarity of a dc supply is reversed, what will happen to the self-excited dc motors connected to these supply lines?
AThe motors will stop
BThe motors will increase speed
CThe motors will rotate in reverse direction
DThe motors will rotate in the same direction
What will happen if the field flux of a dc motor will approach zero?
AThe motor will stop quickly
BThe speed will become dangerously high
CThe motor will burn because the current will become very high
DThe counter emf of the motor will go up quickly to a high value
Which of the following is not necessarily the advantage of dc motors over ac motors?
AHigh starting torque
BWide speed range
CLow cost
DBetter speed control
Which of the following dc motors has the highest no load speed?
ASeries motors
BShunt motors
CCumulative compound motors
DDifferential compound motors
What is the function of the commutator in dc motor?
ATo prevent sparking
BTo reduce friction
CTo convert ac to dc
DTo convert dc to ac
A series motor is best suited to drive which of the following loads?
ALathes
BMachine tools
CShears and punches
DCranes and hoists
The starting torque of a dc motor is independent of the following?
AFlux
BSpeed
CArmature current
DFlux and armature current
Which one is a cause for intermittent sparking at the brushes of a dc motor?
AOpen armature coil
BLoose coupling at the shaft
CIncorrect supply voltage
DIntermittent loads
Which of the following dc motors will be used to - drive intermittent high torque loads?
AShunt motors
BSeries motors
CCumulative compound motors
DDifferential compound motors
How will you reverse the direction of rotation of a self-excited dc motors?
AInterchange the supply connections
BInterchange the armature connections
CInterchange both the armature and field connections
DOpen the field terminals at starting instant
What is the purpose of using carbon brushes in dc motors?
ATo prevent sparking during commutation
BTo prevent overheating on the armature windings
CTo brush off carbon deposits in the commutator
DTo provide a path for current to flow
What is the purpose of retardation test on dc motors?
ATo determine stray losses
BTo determine copper losses
CTo determine friction losses
DTo determine iron losses
Counter EMF is measured using one of the following units. Which one?
AVolt
BKilowatt-hour
CAmpere-hour
DHorsepower
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