Unit 5 MCQ Bank
For
Unit 5 MCQ Bank
For which of the applications a reluctance motor is preferred
A.Electric shavers
B.Refrigerators
C.Singnalling and timing devices
D.Lifts and hoists
✔ View Answer
C.Singnalling and timing devices
✍ Your Comments
A reluctance motor
A.Is self-starting
B.Is constant speed motor
C.Needs no D.C. excitation
D.All of the above
✔ View Answer
D.All of the above
✍ Your Comments
Reluctance motors are
A.Singly excited
B.Doubly excited
C.Either of the above
D.None of the above
✔ View Answer
A.Singly excited
✍ Your Comments
Which of the following motors is generally used in toys
A.Reluctance motor
B.Hysteresis motor
C.Shaded-pole motor
D.Two-value capacitor motor
✔ View Answer
A.Reluctance motor
A dc servomotor is similar to a regular d.c. motor except that its design is modified to cope with
(a) electronic switching
(b) slow speeds
(c) static conditions
(d) both (b) and (c).
Answer:D
A switched reluctance motor differs from a VR stepper motor in the sense that it
(a) has rotor poles of ferromagnetic materia l
(b) rotates continuously
(c) is designed for open-loop operation only
(d) has lower efficiency.
Answer:B
Which of the following motor runs from a low dc supply and has permanently magnetized salient
poles on its rotor ?
(a) permanent-magnet d.c. motor
(b) disk d.c. motor
(c) permanent-magnet synchronous motor
(d) brushless d.c. motor.
Answer:A
A dc servomotor is similar to a regular d.c. motor except that its design is modified to cope with
(a) electronic switching
(b) slow speeds
(c) static conditions
(d) both (b) and (c).
Answer:D
One of the basic requirements of a servomotor is that it must produce high torque at all
(a) loads
(b) frequencies
(c) speeds
(d) voltages.
Answer:C
The most common two-phase ac servomotor differs from the standard ac induction motor
because it has
(a) higher rotor resistance
(b) higher power rating
(c) motor stator windings
(d) greater inertia.
Answer:A
A switched reluctance motor differs from a VR stepper motor in the sense that it
(a) has rotor poles of ferromagnetic materia l
(b) rotates continuously
(c) is designed for open-loop operation only
(d) has lower efficiency.
Answer:B
A variable reluctance stepper motor is constructed of ……………… material with salient poles.
(a) paramagnetic
(b) ferromagnetic
(c) diamagnetic
(d) non-magnetic
Answer: B
Ques. In a three-stack 12/8-pole VR motor, the rotor pole pitch is
(a) 15º
(b) 30º
(c) 45º
(d) 60º
Answer: C
Ques. A stepper motor having a resolution of 300 steps/rev and running at 2400 rpm has a pulse
rate of— pps.
(a) 4000
(b) 8000
(c) 6000
(d) 10,000
Answer: C
Ques. If a hybrid stepper motor has a rotor pitch of 36º and a step angle of 9º, the number of its
phases must be
(a)4
(b)2
(c)3
(d)6
Answer: A
Ques. The rotor of a stepper motor has no
(a) windings
(b) commutator
(c) brushes
(d) all of the above.
Answer: D
Ques. A stepping motor is a ……………… device.
(a) mechanical
(b) electrical
(c) analogue
(d) incremental
Answer: D
Ques. The rotational speed of a given stepper motor is determined solely by the
(a) shaft load
(b) step pulse frequency
(c) polarity of stator current
(d) magnitude of stator current.
Answer: B
Ques. Which of the following phase switching sequence represents half-step operation of a VR
stepper motor ?
(a) A, B, C, A …………………..
(b) A, C, B, A …………………..
(c) AB, BC, CA, AB …………………..
(d) A, AB, B, BC …………………..
Answer: D
Ques. A stepper motor may be considered as a ……………… converter.
(a) dc to dc
(b) ac to ac
(c) dc to ac
(d) digital-to-analogue
Answer: D
Ques. What is the step angle of a permanent-magnet stepper motor having 8 stator poles and 4
rotor poles ?
(a) 60º
(b) 45º
(c) 30º
(d) 15º
Answer: B
Ques. Wave excitation of a stepper motor results in
(a) microstepping
(b) half-stepping
(c) increased step angle
(d) reduced resolution.
Answer: B
Ques. The torque exerted by the rotor magnetic field of a PM stepping motor with unexcited
stator is called ………………torque.
(a) reluctance
(b) detent
(c) holding
(d) either (b) or (c)
Answer: D
Ques. A single-stack, 4-phase, 6-pole VR stepper motor will have a step angle of
(a) 15º
(b) 30º
(c) 45º
(d) 90º
Answer: A
This set of DC Machines Multiple Choice Questions & Answers (MCQs) focuses on “BLDC
Motors”.
In BLDC motor field winding is kept on _______________
a) Stator
b) Rotor
c) Can be placed anywhere
d) Absent
View Answer
Answer: b
Explanation: Unlike conventional DC motor, BLDC motor has its field winding rotating. Unlike
PMDC motor field winding is present. Thus, it is placed on rotor. In BLDC motor we have fixed
commutators, with brush gear rotating with speed of rotor field.
By electronic circuitry BLDC can be controlled for both constant and variable torque operation.
a) True
b) False
View Answer
Answer: a
Explanation: In BLDC because of rotor position feedback triggering of thyristors/transistors, the
stator and rotor field always remain in synchronism as the frequency of triggering automatically
adjusts to motor speed. The length of on-time of the transistors determines motor torque
magnitude.
Which of the following is not an advantage of BLDC motor over conventional DC motor.
a) Less maintenance
b) Long life
c) No risk of explosion or possibility of RF radiation
d) Low cost
View Answer
Answer: d
Explanation: The brushless DC motor being more expensive compare to DC motor of same kW
ratings, serves many other advantages like long life, less maintenance, rapid response, linear
characteristic, no sparking and many more.
In BLDC motor driver module, we do not require ______________
a) SCRs
b) Power transistors
c) FETs
d) Transistors
View Answer
Answer: d
Explanation: The stator is connected to a variable voltage current source through an inductor and
an inverter comprising six SCRs (S1 to S6). In place of SCRs, power transistor or FETs could be
used according to power rating of the motor.
In medical fields which DC motor is widely used?
a) PMDC
b) BLDC
c) Brushed DC motor
d) Cannot be determined
View Answer
Answer: b
Explanation: BLDC motors are widely used in various applications of medical industry. Sensor
less BLDC motor and with sensor BLDC motors are used because of easy operation and high
reliability compare to conventional motors.
Construction of BLDC is exactly similar to the ______________
a) Conventional DC motor
b) Induction motor
c) Permanent magnet synchronous motor
d) Totally different construction
View Answer
7. Typical brushless motor doesn’t have ______________
a) Commutator
b) Permanent magnet
c) Electronic controller
d) Fixed armature
View Answer
Answer: a
Explanation: A typical brushless motor has permanent magnets which rotate around a fixed
armature. An electronic controller replaces the brush-commutator assembly of the brushed
conventional DC motor, which continually switches the phase to the windings to keep the motor
turning.
8. BLDC can be used instead ____________
a) Synchronous motor
b) Normal brushed DC motor
c) Induction motor
d) Air motor
View Answer
Answer: b
Explanation: Brushless motors fulfil almost all functions originally performed by brushed DC
motors, but cost and control complexity prevent brushless motors from replacing brushed motors
completely in the lowest-cost areas. Brushless motors are now dominating many applications,
particularly devices such as computer hard drives and CD/DVD players.
0 Comments