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WorksheetsElectrician 3rd Sem Module 3 AC Three Phase Motor 61-87
Total questions: 27
Worksheet time: 14mins
Name
Class
Date
1.
What is the reason of long chord winding is avoided in AC motors?
a)
Low efficiency
b)
Low starting torque
c)
More winding wire required
d)
Less heat dissipation
2.
Which type of winding has more space for cooling?
a)
Between overhanging coils
b)
Between overhanging coil and rotor
c)
Between overhanging coils and yoke
d)
Between overhanging coil and wedge
3.
Where the panel boards are used?
a)
Industrial motor drives
b)
Domestic wiring circuits
c)
3 phase domestic wiring
d)
Load distribution for AC & DC supply
4.
Determine the torque in newton metres produced by a 7.5 HP squirrel cage motor rotating at 1440 rpm?
a)
21.63 Nm
b)
24.4 Nm
c)
33.05 Nm
d)
36.6 Nm
5.
Which type of handle design of rotary switch is illustrated?
a)
Knob
b)
Lever
c)
Coin slot
d)
Key operation
6.
What is the purpose of using rotor resistance starter to start 3 phase slip ring induction motor?
a)
Reduce rotor voltage
b)
Reduce rotor current
c)
Increase the torque
d)
Reduce the power loss
7.
Which method of speed control is only applicable for 3 phase slipring induction motor?
a)
Cascade operation method
b)
Rotor rheostat speed control
c)
Changing the applied frequency method
d)
Changing the number of stator poles method
8.
What is the name of the winding?
a)
Skew winding
b)
Skein winding
c)
Involute coil winding
d)
Diamond coil winding
9.
What is the name of 3 phase motor winding, if the coil pitch is less than pole pitch?
a)
Full pitch winding
b)
Whole coil winding
c)
Long chorded winding
d)
Short chorded winding
10.
Which is the demerit of 3 phase concentric winding?
a)
More space is required
b)
A stepped former is required
c)
More difficult to shape the coils uniformly
d)
It is not easy to make the end connection
11.
What is the name of the diagram used for 3phase motor winding?
a)
Ring diagram
b)
Development diagram
c)
Coil connection diagram
d)
End connection diagram
12.
Calculate the phase displacement in terms of slots for a 3 phase, 36 slots, 12 coils, 4 pole stator winding?
a)
3 slots
b)
4 slots
c)
6 slots
d)
8 slots
13.
Which type of AC motor winding having the number of coil/pole/phase is more than one arranged in different slots?
a)
Basket winding
b)
Concentric winding
c)
Distributed winding
d)
Concentrated winding
14.
Which type of testing of winding is illustrated?
a)
Polarity test
b)
Resistance test
c)
Short circuit test
d)
Voltage drop test
15.
Why external resistance is included in the rotor circuit at starting through 3 phase slipring induction motor starter?
a)
To get high running torque
b)
To get high starting torque
c)
To reduce the load current
d)
To get increased speed at starting
16.
What is the effect of motor, if the rotor windings in slipring induction motor is open circuited at starting?
a)
Will not run
b)
Runs at slow speed
c)
Runs at very high speed
d)
Runs but not able to pull load
17.
What happens to a 3 phase induction motor if one phase fails during running?
a)
Motor runs normally
b)
Motor stop instantaneously
c)
Motor runs slowly, finally it burns
d)
Motor runs with irregular speed
18.
What is the effect on 3 phase induction motor if one phase is cut-off during running with load?
a)
Motor stops at once
b)
Motor will run normally
c)
Motor runs with humming noise with slow speed
d)
Motor will run slow speed but winding will be burnt out shortly
19.
What is the defect, if starter with single phasing preventer does not switch ‘ON’?
a)
Improper phase sequence
b)
Fluctuations in line voltage
c)
Loose contact in supply lines
d)
Wrong terminal connections at motor
20.
What is the defect in AC 3 phase induction motor runs at low speed if loaded?
a)
Wrong motor connection
b)
Wrong starter connection
c)
Open circuit in rotor winding
d)
Partially shorted stator winding
21.
Which fault condition thermal overload relay protects A.C induction motor?
a)
Short circuit
b)
Open circuit
c)
Over current
d)
Under voltage
22.
What happens to the rotor of a 3 phase induction motor if its speed attains to synchronous speed?
a)
Rotor speed reduces
b)
Rotor speed increases
c)
Rotor speed remains same
d)
Rotor bars get damaged
23.
What is the effect of open circuit in rotor of an induction motor?
a)
Motor does not start
b)
Over heating in motor
c)
Excess vibration of shaft
d)
Motor runs with very low speed
24.
What is the reason for frequent blowing of fuse after motor running some time?
a)
Improper earthing
b)
Over loading of motor
c)
Heavy voltage fluctuation
d)
Poor insulation in winding
25.
What happens to a 3 phase induction motor, if one phase fails during starting?
a)
Motor runs and stop immediately
b)
Motor runs in slow speed continuously
c)
Motor runs and draws more current
d)
Motor continues to run with irregular speed
26.
Which is the cause for the 3 phase motor starter with single phase preventer trips frequently?
a)
Incorrect fuse ratings
b)
Unbalanced line voltage
c)
Incorrect settings of OLR
d)
Improper phase sequence
27.
What indication denotes the shorted coil defect in 3 phase motor stator winding while testing with internal growler by keeping hacksaw blade?
a)
Hacksaw blade gets over heated
b)
Rapid vibration of hacksaw blade
c)
Hacksaw blade repels against the slots
d)
Attracted by the winding turns on the slot
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