300 Important DC Motor MCQ Questions & Answers with Explanation | PDF Free Download
1.High inrush of current during a starting of a dc motor can efficiently be restricted to a safer value by increasing the _________ resistance.
- AShunt field
- BArmature circuit
- CBoth a and b
- DNone of these
2.The dc motor draws high current at the starting instant due to absence of back emf. In order to prevent this high inrush of current at start, a resistance is connected
- AAcross the field
- BAcross the armature
- CIn series with the armature
- DIn series with the filed
3.For efficient operation of a dc motor, the additional resistance inserted in the armature circuit should be
- AIncreased in steps
- BCut out in steps
- CLeft in the armature circuit
- DRemoved immediately after start
4.In dc shunt motors, at start the field excitation is kept at maximum value in order to
- AReduce starting torque
- BIncrease acceleration duration
- CReduce armature heating
- DAvoid voltage dip in the supply mains
5.Direct on line (DOL) starters are not suitable for starting large dc motors, because
- AThe starting current will be enormously high, which will cause large voltage drop in the supply mains
- BThe motor may not start
- CThe motor may run away
- DThe starting torque becomes low
6.A DOL starter is employed for starting motors of ratings up to
- A3.75 kW
- B7.5kW
- C1.5kW
- D25kW
7.In a dc shunt motor, the three-point starter
- ALimits the starting current to a safer value
- BProvides overload protection
- CProvides no volt protection
- DAll of the above
8.Three-point starters are not suitable for application where speed variation by flux control is required because the motor may
- ANot start
- BRun away
- CStop at very high speed
- DStop at very slow speed
9.If the no-voltage release in a dc motor starter fails to operate on failure of supply, on resumption of supply the motor will
- ANot start automatically
- BStart automatically without trouble
- CDevelop very low starting torque
- DGet damaged due to flow of excessive current in the armature
10.The dc motor starter handle should be moved
- AVery slowly in steps
- BSmoothly in steps
- CQuickly
- DWith a jerk to final position
11.DC motors are stopped by opening the line switches and not by forcing the handle of the motor starter back to OFF position. This is due to occurrence of
- AHeavy sparking at the first stud of the starting resistance steps
- BHeavy sparking at the brushes
- CBoth (a) & (b)
- DNone of these
12.A 4-point starter is used to start and control the speed of a
- Adc shunt motor with armature resistance control
- Bdc shunt motor with field weakening control
- Cdc series motor
- Ddc compound motor
13.In a dc compound motor, 4-point starter is employed
- Ato reduce the field current
- Bto increase the field current
- Cnot to affect the current flowing through Hold On coil even when the field current changes
- Dnone of the above
14.In a dc compound motor, 4-point starter provides
- AOver load protection
- BUnder voltage protection
- CThe facility for wide range of speed control by field regulator
- DAll of the above
15.A large dc shunt motor can be started preferably using a
- ACompensator
- BStrong field
- CWeak field
- DNone of these
16.The simplest form of a motor controller is
- ARelay
- BToggle switch
- CDrum switch
- DMagnetic switch
17.The most economical method of electric braking is
- APlugging
- BDynamic braking with separate excitation
- CDynamic braking with self-excitation
- DRegenerative braking
18.The electric braking system employed with dc shunt motors, in which the armature connections are reversed so that the motor tends to run in opposite direction is called the ____braking
- APlugging
- BRheostatic
- CDynamic
- DRegenerative
19.Plugging of dc machine is normally executed by
- AReversing the field polarity
- BReversing the armature polarity
- CReversing both field and armature polarity
- DConnecting the resistance across armature terminals
20.A dc shunt motor, running lightly at 1,000 rpm, is operated under plugging. With plugging connection left as it is the final speed of the motor will be
- AZero
- B1,000 rpm
- C-1000 rpm
- D-2000 rpm