Electrical Machines 2

Question 1

High speed and high starting applications such as coil winders, lifts etc.
A. Stepper motor
B. Universal motor
C. Repulsion motor
D. Synchronous motor

Answer 1

C. Repulsion motor

Question 2

Rotates in a series of small angular steps, rather than continuously.
A. Repulsion motor
B. Synchronous motor
C. Universal motor
D. Stepper motor

Answer 2

D. Stepper motor

Question 2

A type of motor that can be operated using single phase AC supply or a DC supply.
A. Synchronous motor
B. Stepper motor
C. Repulsion motor
D. Universal motor

Answer 2

D. Universal motor

Question 2

What is the maximum speed at which a 50 Hz synchronous machine can be operated?
A. 3000 rpm
B. 3600 rpm
C. 3200 rpm
D. 3400 rpm

Answer 2

A. 3000 rpm

Question 3

What is the percent slip of the synchronous motor when running?
A. 2
B. 1
C. 3.5
D. 0

Answer 3

D. 0

Question 3

Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to adjust the grid’s voltage, or to improve power factor.
A. Alternator
B. Synchronous compensator
C. Generator
D. Synchronous reactor

Answer 3

B. Synchronous compensator

Question 4

When the frequency of a synchronous motor increases, what happens to its speed?
A. Remains the same
B. None of these
C. Decreases
D. Increases

Answer 4

D. Increases

Question 5

It has a double excitation and with an armature winding which supplied by an AC source and Field winding which is supplied by a DC source.
A. Asynchronous generator
B. Induction motor
C. Alternator
D. Synchronous motor

Answer 5

D. Synchronous motor

Question 6

The speed of asynchronous type motor is _____ than synchronous type motor?
A. Low
B. Zero
C. Equal
D. High

Answer 6

A. Low

Question 7

Which of the following component of induction motor holds 3 phases of supply?
A. Rotor
B. Load
C. All of the above
D. Stator

Answer 7

D. Stator

Question 8

Which of the following component of induction motor holds windings with shorted?
A. All of the above
B. Load
C. Rotor
D. Stator

Answer 8

C. Rotor

Question 9

Torque in asynchronous type motor during its operation is developed on _____?
A. Stator windings
B. Load
C. Magnet
D. Rotor conductors

Answer 9

D. Rotor conductors

Question 10

A synchronous type of motor has a speed of _____ limit?
A. Constant
B. Zero
C. Variable
D. Infinity

Answer 10

A. Constant

Question 11

At which condition do synchronous type of motor reaches rest?
A. Load is greater on shaft of motor
B. Load is less on shaft of motor
C. Load is equal on shaft of motor
D. No load condition

Answer 11

A. Load is greater on shaft of motor

Question 12

These are the different starting methods for synchronous motor, except:
A. Using prime mover
B. Using DC motor
C. Using damper windings
D. Using another synchronous motor

Answer 12

D. Using another synchronous motor

Question 13

It operates at a lagging power factor only.
A. Synchronous motor
B. Induction generator
C. Asynchronous generator
D. Induction motor

Answer 13

D. Induction motor

Question 14

In correcting power factor, synchronous motors operate at
A. No load with over-excited fields
B. Normal load with zero excitation
C. No load with under-excited fields
D. Normal load with maximum excitation

Answer 14

A. No load with over-excited fields

Question 15

The speed regulation of a synchronous motor is
A. 100%
B. 0%
C. 25%
D. 50%

Answer 15

B. 0%

Question 16

The breakdown torque will be proportional to ________ for synchronous motor.
A. 1/(V^2)
B. Applied voltage V
C. V^2
D. 1/V

Answer 16

B. Applied voltage V

Question 17

Hunting occurs due to ________
A. Small and constant load
B. Periodic Variation
C. Over loading for long periods
D. Over excitation

Answer 17

B. Periodic Variation

Question 18

At any power factor, it can operate in low speed but high-power application.
A. Induction generator
B. Synchronous motor
C. Asynchronous generator
D. Induction alternator

Answer 18

B. Synchronous motor

Question 19

Magnetizing current is zero and motor operates at unity power factor.
A. Normally non-excited synchronous motor
B. Normally excited synchronous motor
C. Over excited synchronous motor
D. Under excited synchronous motor

Answer 19

B. Normally excited synchronous motor

Question 20

Leading reactive VA supplied by the source and which operates at leading power factor
A. Normally excited synchronous motor
B. Under excited synchronous motor
C. Normally non-excited synchronous motor
D. Over excited synchronous motor

Answer 20

D. Over excited synchronous motor

Question 21

Insufficient to produce an air gap that which requires by the supply voltage.
A. Over excited synchronous motor
B. Normally non-excited synchronous motor
C. Under excited synchronous motor
D. Normally excited synchronous motor

Answer 21

C. Under excited synchronous motor

Question 21

Voltage limiting device are connected at _____________ in a wound rotor induction motor to reduce voltage starting.
A. Panel board
B. Field
C. Stator
D. Rotor

Answer 21

C. Stator

Question 22

Power developed in the induction motor can be obtain using the formula ______
A. ((1-s)/s)(rotor copper loss)
B. (1-s)(Rotor copper loss)
C. ((1-s)/s)(Rotor power input)
D. (1-s)/rotor copper loss

Answer 22

A. ((1-s)/s)(rotor copper loss)

Question 23

Power input of the rotor can be obtain using what formula?
A. (s)(rotor copper loss)
B. (s)(power developed)
C. (rotor copper loss)/s
D. (s)/(rotor copper loss)

Answer 23

C. (rotor copper loss)/s

Question 24

Which of the following is true about getting the answer for rotor power input?
A. (s)/(rotor copper loss)
B. (rotor copper loss)/(1-s)
C. (1-s)/(power developed)
D. (power developed)/(1-s)

Answer 24

D. (power developed)/(1-s)

Question 25

The rotor of a 3 phase, 60 Hz, 4 pole induction motor takes 120 kW at 3Hz. What is the rotor speed of the induction motor?
A. 1710 rpm
B. 1800 rpm
C. 1810 rpm
D. 1700 rpm

Answer 25

A. 1710 rpm