Deck 3: Motor for Various Applications

Question 1

The travelling speed of cranes varies from

A)20 to 30 m/s
B)10 to 15 m/s
C)5 to 10 m/s
D)1 to 2.5 m/s

Answer 1

1 to 2.5 m/s

Question 2

Besides a constant speed a synchronous rotor possesses which of the following advantages ?

A)Lower cost
B)Better efficiency
C)High power factor
D)All of the above

Answer 2

High power factor

Question 3

By the use of which of the followingm D.C. can be obtained from AC?

A)Silicon diodes
B)Mercury arc rectifier
C)Motor generator set
D)Any of the above

Answer 3

Any of the above

Question 4

Which of the following motors is preferred when quick speed reversal is the main consideration?

A)Squirrel cage induction motor
B)Wound rotor induction motor
C)Synchronous motor
D)D.C.motor

Question 5

Which of the following motors is preferred when smooth and precise speed control over a wide range is desired ?

A)D.C.motor
B)Squirrel cage induction motor
C)Wound rotor induction motor
D)Synchronous motor

Question 6

For crane travel which of the following motors is normally used ?

A)Synchronous motor
B)D.C.differentially compound motor
C)Ward-Leonard controlled
D)C.shunt motor

Question 7

The capacity of a crane is expressed in terms of

A)type of drive
B)span
C)tonnes
D)any of the above

Question 8

The characteristics of drive for crane hoisting and lowering are which of the following ?

A)Precise control
B)Smooth movement
C)Fast speed control
D)All of the above

Question 9

Which of the following motors is preferred for boom hoist of a travelling crane?

A)Single phase motor
B)Synchronous motor
C)A.C.slip ring motor
D)Ward-Leonard controlled D.C.shunt motor

Question 10

A wound rotor induction motor is preferred, as compared to squirrel cage induction motor, when major consideration is

A)slop speed operation
B)high starting torque
C)low windage losses
D)all of the above

Question 11

Which of the following motors has series characteristics ?

A)Shaded pole motor
B)Repulsion motor
C)Capacitor start motor
D)None of the above

Question 12

Which of the following happens when star-delta starter is used ?

A)Starting voltage is reduced
B)Starting current is reduced
C)Both (A) and (B)
D)None of the above

Question 13

For a D.C. shunt motor which of the following is incorrect 7

A)Unsuitable for heavy duty starting
B)Torque varies as armature current
C)Torque-armature current is a straight line
D)Torque is zero for zero armature current

Question 14

For which of the following applications motor has to start with high acceleration?

A)Oil expeller
B)Floor mill
C)Lifts and hoists
D)Centrifugal pump

Question 15

Which of the following types of motor enclosure is safest ?

A)Totally enclosed
B)Totally enclosed fan cooled
C)Open type
D)Semi closed

Question 16

While selecting motor for an air conditioner which of the following characteristics is of great importance ?

A)Type of bearings
B)Type of enclosure
C)Noise
D)Arrangement for power transmission

Question 17

The diameter of the rotor shaft for an electric motor depends on which of the following ?

A)r.p.m.only
B)Horse power only
C)Horse power and r.p.m.
D)Horse power, r.p.m.and power factor

Question 18

Which of the following alternatives will be cheaper ?

A)A 100 H.P.AC.three phase motor
B)Four motors of 25 H.P.each
C)Five motors of 20 H.P.each
D)Ten motors of 10 H.P.each

Question 19

The cost of an induction motor will increase as

A)horsepower rating increases but r.p.m.decreases
B)horsepower rating decreases but r.p.m.increases
C)horsepower rating and operating speed increases
D)horsepower rating and operating speed decreases

Question 20

In series motor which of the following methods can be used for changing the flux per pole ?

A)Tapped field control
B)Diverter field control
C)Series-parallel control
D)Any of the above

Question 21

Word Leonard controlled DC Drives are generally used for..... excavators

A)Light duty
B)Medium duty
C)Heavy duty
D)All of the above

Question 22

......... is preferred for automatic drives

A)Synchronous motors
B)Word Leonard controlled DC motors
C)None of the above
D)Any of the above

Question 23

The load cycle for a motor driving a power press will be .........

A)Variable load
B)Continuous
C)Continuous but periodical
D)Intermittent and variable load

Question 24

A reluctance motor........

A)Is provided with slip rings
B)Requires starting gear
C)Has high cost
D)Is compact

Question 25

The size of an excavator is usually expressed in terms of

A)Crowd motion
B)Angle of swing
C)Cubic metres
D)Travel in metres