WorksheetsAC Machines Technical Quiz
Total questions: 20
Worksheet time: 40mins
The basic function of a transformer is to change
the level of the voltage
the power level
the power factor
the frequency
In a shaded pole motor, shading coils are using to
reduce winding losses
reduce friction losses
produce rotating magnetic field
protect against sparking
The capacitor in a capacitor-start induction run ac motor is connected in series with
starting winding
running winding
squirrel cage winding
compensating winding
why is a centrifugal switch used in a 1-ph induction motor
To protect the motor from overloading
To improve the starting performance of the motor
To cut off the starting winding at an appropriate instant
d) To cut in the capacitor during running conditions
Induction generators deliver power at
Leading power factor only
Lagging power factor only
Leading as well as lagging power factor
Unity power factor only
The method that gives continuous speed control of a slip-ring induction motor is
Rotor resistance control
Secondary foreign voltage control
Concatenation or cascade operation
Line voltage control
During plugging of an induction motor
Phase sequence is reversed
A dc source is connected to stator
One phase is open-circuited
v
The good power factor of an induction motor can be achieved if the average flux density in air gap is
Large
Small
Infinite
Absent
An induction motor with 1000 rpm speed will have __________ poles
2
6
4
8
Which of the following equipment will draw the reactive power?
Electrical iron
Tubelight
Three phase motor
rectifier
The large number of narrow slots in stator of an a.c. motor is preferred because
It is easier to make narrow slots than wide open slots
Large number of narrow slots reduces motor noise
Large number of narrow slots reduces noise and tooth pulsation losses
It helps in uniform distribution of flux
The alternators are normally designed for the torque angle of the order of
3° to 5°
2 rad to 3 rad
15° to 30°
1° to 3°
Which of the synchronous alternators will complete 1080 electrical degrees in one revolution?
8 pole synchronous alternator
6 pole synchronous alternator
4 pole synchronous alternator
10 pole synchronous alternator
How many cycles of alternating current will be generated in one revolution of 8 pole synchronous alternator?
10 cycles
4 cycles
8 cycles
16 cycles
How many poles will be required if an alternator runs at 1500 rpm and given frequency of 50 Hz?
8 pole
6 pole
4 pole
2 pole
Which of the following statements is correct?
A single phase induction motor has very high starting torque.
A single phase induction motor has zero starting torque.
A single phase starting torque is as good as that of 3 phase induction motor.
A single phase motor has very small torque but greater than zero.
The synchronous motor can be made self starting by providing.
Damper winding on rotor poles
Damper winding on stator
(a) and (b)
None of the above
The air cores in transformers are preferred for
Low frequency transformers
High frequency transformers
5 kVA, 50 Hz transformers
None of these
Which material has the highest conductivity of all materials?
Silver
Copper
Gold
Tungsten
Which part of transformer is subjected to maximum heating?
Frame
Core
Winding
Oil
