What is the usual speed of a dc series motor at no load?
AZero
BVery high
CAround 500 to 1000 rpm
DAround 3000 to 3600 rpm
Electrical Engineering · Question Bank
DC Motors
218 of 285 questions match · page 6 of 11. Answer in your head first, then check the solution.
How do you call the variable resistor shunting the field of a series dc motor?
AVoltage regulator
BPotential divider
CField diverter
DArmature diverter
The yoke of a dc motor is normally made from which of the following materials?
AMica
BSteel
CCopper
DIron
What will happen to a dc series motor when connected across an ac supply?
AIt will develop a torque in the same direction
BIt will not develop any torque
CIt will draw dangerously high current
DIt will develop a pulsating torque
As compared to shunt and compound motors, a series motor has the highest starting torque due to which of the following?
AWeak series field at start
BLarge armature current at start
CLower armature current at start
DStronger series field at start
What is the function of the commutator in a dc motor?
AIt will prevent sparking between brushes and armature windings
BIt will convert alternating current to direct current
CIt will convert direct current to alternating current
DIt will reduce the friction and windage losses
A “brake test” is applicable only in which of the following types of dc motors?
ASmall horsepower motors
BHigh speed motors
CSeparately-excited motors
DOpen frame type motors
Which of the following is used to vary the speed of a dc motor?
AVary its flux per pole
BVary the resistance of its armature circuit
CVary the applied voltage
DAll of these
Which of the following dc motors has the best speed regulation?
ASeries motor
BShunt motor
CDifferential compound motor
DCumulative compound motor
Which one limits the maximum torque on a dc motor?
AHeating
BSpeed
CCommutation
DMechanical loss
Differential compound dc motors are applicable in which of the following load conditions?
AHigh starting torque loads
BLow starting torque loads
CFrequent on-off cycle loads
DVariable speed loads
Which one is main advantage of the Swinburne’s test on dc motors?
AIt is very economical and convenient
BIt ignores any change in the iron loss
CIt needs only one running test
DIt is applicable to both shunt and compound motors
Which one is main advantage of the Ward-Leonard system of dc motor speed controls?
AIt can be used for small motors
BIt has a high overall efficiency at all speeds
CIt uses a flywheel to reduce fluctuations in power demands
DIt gives smooth, sensitive and wide speed controls
What will happen if the supply terminals of a self-excited dc motor are interchanged?
AThe motor will run at its normal speed and in the same direction
BThe motor will run at its normal speed but in reverse direction
CThe motor will not run
DThe motor will run but at a lower speed
Which of the following is a function of the pole shoes in a dc motor?
ATo support the field coils
BTo spread out the flux
CTo reduce the reluctance of the magnetic path
DAll of these
Which one is an indication of a hot smoky motor?
AMotor windings are opened
BMotor windings are shorted
CMotor windings are grounded
DBoth B and C
At what size of loading is the back emf of a dc motor maximum?
AAt full load
BAt 50% load
CAt no load
DAt overload
What will happen to a dc series motor if plugged to an ac source at the same voltage?
AIt will run but with less efficiency
BIt will run slowly
CIt will overheat and get burn
DIt will not run
The operation of electric motors and generators depends on the interaction between the magnetic field and one of the following. Which one?
AElectric current
BElectric field
CCopper conductors
DBoth A and B
The bigger percentage of the power loss in a dc motor comes from which of the following?
AIron loss
BCopper loss
CStray power loss
DWindage loss
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