300 Important DC Motor MCQ Questions & Answers with Explanation | PDF Free Download
1.In plugging of a dc shunt motor, the resistance is inserted in the armature circuit to
- AIncrease the braking torque
- BStop the motor quickly
- CLimit the armature current
- DHave a shorting effect on the shunt field
2.The plugging provides _______ braking torque in comparison to rheostat and regenerative braking systems
- ANegligible
- BSmall
- CHighest
- DNone
3.The electric braking system commonly employed in rolling mills, elevators and printing presses is
- APlugging
- BRheostatic
- CDynamic
- DRegenerative
4.The dynamic braking is generally used with ____dc motors
- ASeries
- BShunt
- CCompound
- DAll
5.Dynamic braking is very effective if the dc motor
- Ais series excited
- Bis shunt excited
- Cis separately excited
- Dhas cumulative compound excitation
6.For non-reversing dc drives it is preferable to use
- Aplugging
- Bregenerative braking
- Cdynamic braking with separate excitation
- Ddynamic braking with self-excitation
7.During rheostatic braking of dc series motors
- AThe speed is reduced
- BThe direction of rotation is reversed
- CThe machine operates as a generator
- DNone of the above
8.Regenerative braking is based on that the back emf is
- AZero
- BEqual to applied voltage
- CLess than applied voltage
- DMore than applied voltage
9.In regeneration breaking, the motor energy is
- ADissipated I in armature heating
- BDissipated in windage losses
- CReturned to the supply mains
- DNone of the above
10.Regenerative braking
- ACan be easily applied to dc shunt motors
- BCan be easily applied to dc series motors
- CCan be used for stopping the motor
- DCannot be used when the load on motor has over hauling characteristics
11.Field copper losses are constant in dc ____motors
- ASeries
- BShunt
- CCompound
- DNone
12.The variable loss in a dc shunt machine is
- AIron loss
- BShunt field loss
- CArmature copper loss
- DFriction and windage loss
13.Two series motors are mechanically coupled. One machine is running as a motor and the other as a generator. The iron and friction losses of the machines will be identical when
- Atheir speeds are identical
- Btheir speeds and excitations are identical
- Ctheir speeds are equal but back emfs are half the supply voltages
- Dtheir ratings and armature sizes are identical
14.In a dc machine mechanical loss occur due to
- Aair resistance of rotation to armature and fan
- Bbrush friction
- Cbearing friction
- Dall of the above
15.In a dc machine, mechanical losses are primarily function of
- Avoltage
- Bcurrent
- Cspeed
- Dnone of these
16.The loss in a dc machine, which has the least proportion is
- Amechanical loss
- Biron loss
- Carmature copper loss
- Dfield copper loss
17.Hysteresis loss in a dc machine is independent of
- AVolume and grade of iron
- BFrequency of magnetic reversals
- CRate of flow of air
- DMaximum value of flux density
18.In a dc machine, which loss increases rapidly with the increase in frequency of magnetic reversals?
- ACopper loss
- BHysteresis loss
- CEddy current loss
- DMechanical loss
19.The core (or iron ) losses, in a dc machine occur due to
- AEddy current loss only
- BHysteresis loss only
- CBoth hysteresis and eddy current losses
- DAir friction only
20.Core loss in a dc machine occurs in
- AArmature only
- BPole shoe only
- CYoke only
- DIn all the above three