Download model test ( sem-iii)

ELECTRICIAN TRADE THEORY
SEMESTER- III
Time:-1.5Hrs
Marks:-75
Note :- Attempt All Question. All question carry equal marks.
CHOOSE THE CORRECT ANSWER.
1. The magnetic field produced in the stator of
a three phase induction motor travels at ……..
A. rotating speed
B. asynchronous speed
C. synchronous speed
D. slip speed.
2. In an induction motor the fractional slip(S) is
indicated by the expression……..
A. S= (Nr-Ns)/Ns B. S= (Ns-Nr)/Ns
C. S= (Nr-Ns)/Nr D. S= (Ns-Nr)/Nr
3. The fractional slip of an induction motor
having a synchronous speed of 25 rev/s and a rotor
speed of 23.75 rev/s is ….
A. 0.05
B. 0.03
C. 0.02
D. 0.00
4. Which of the following formula is used to
calculate the synchronous speed of an induction
motor?
A. Ns= Pxf
B. Ns= 120xP/f
C. Ns= 120xf/P
D. Ns= fxP/120
5. A 3-phase, 400V, 50Hz induction motor has a
rated speed of 715 r.p.m How many poles are
there in the rotating magnetic field?
A. 2 poles
B. 4 poles
C. 6 poles
D. 8 poles
6.For a small capacity induction motor, the type of
starter used is ……..
A. star-delta starter
B. D.O.L starter
C. auto transformer starter
D. step-down transformer starter.
7. The two primary parts of a squirrel cage
induction motor are ………….
A. rotor and stator
B. stator and
field
C. slip rings and brush
D. rotor and armature
8. When compared to the main contacts, auxiliary
contacts carry …………..
A. less voltage
B. higher load
C. less current
D. additional power, supporting main contacts.
9. An ON-OFF switch with a no-volt coil is called
a ……….
A. magnetic starter
B.
manual
starter
C. reversing starter
D. combination
starter
10. Which of the following reduces vibration,
chattering, noise, wear and head in the armature of
a starter magnetic core?
A. shading coil
B. electromagnet
C. holding- circuit interlock
D. centrifugal switch.
11. Thermal overload relay is provided in a starter
to protect the motor against …………
A. short circuit
B. open circuit
C. excess current
D. low voltage.
12. Line voltage of a star-connected, 3-phase
circuit is 415 V. The phase voltage will be ……..
A. 415 V
B. 210 V
C. 220 V
D. 230 V
13. The phase current of a delta-connect, 3-phase
circuit is 100 amps. The line current will be
………
A. 77.8A
B. 100A
C. 173A
D. 300A
14. The approximate full load current of a 3-phase
delta-connected 3 HP motor is …….
A. 4.5A
B. 3.5A
C. 2.5A
D. 1.5A
15. Metric horse power is equal to ………
A. 746W
B. 736W
C. 1000W
D.1730W
16. In a split-phase capacitor start induction
run motor a time phase difference between the
currents in the main and auxiliary windings is
achieved by ……..
A. placing the two windings at an angle of 180
electrical degrees in the stator slots
B. applying two-phase supply across the two
windings
C. introducing capacitive reactance in the auxiliary
winding circuit
D. connecting the two windings in series across a
single phase supply.
20. A capacitor start induction-run single phase
motor has its capacitance replaced by an inductor
of equivalent reactance value. If the motor is
connected to the supply, it will ……….
A. run in the reverse direction
B. not start with load
C. run with lower torque taking lower current
D. start but will not take load
21. Universal motor gives shock because …...
17. The direction of rotation of a capacitor-stator
motor can be reversed by……..
A. reversing the supply terminal connections
B. reversing the connections of the auxiliary
winding only
C. reversing the connections of either the main
winding or the auxiliary winding terminals
D. reversing the connections of the main winding
only.
18. The purpose of the starting capacitor in a
capacitor-start induction-run motor is ….
A. to increase the starting torque and decrease the
starting current
B. to decrease the starting torque and decrease the
starting current
C. to increase the starting current and increase the
starting power factor
D. to decrease the starting current and decrease the
starting power factor.
19. Which of the following types of capacitors is
preferred for the starting circuit of a single phase
capacitor start induction-run motor of 2 HP rating?
A. Paper capacitor of continuous rating
B. Ceramic capacitor of intermittent rating
C. Mica capacitor of continuous rating
D. Electrolytic capacitor of intermittent rating
A. short in the armature winding and poor earthing
B. motor running above the normal rated speed
C. applied voltage is very low
D. grounded field due to weak insulation and poor
earthing.
22. Motor gives humming noise when running
…….
A. short circuited field coil
B. loose connection in foundation bolts
C. motor takes less current
D. motor runs under no load.
23. Direction of rotation of universal motor can be
changed ……
A. by interchange the armature connections only
B. by interchanging the field connections only
C. by interchanging either the field or armature
connection
D. none of the above.
24. The slip rings are generally made up of …..
A. aluminium
C. carbon
B. copper
D. phosphor bronze
25. A three-phase slip ring induction motorhas
…….
A. a short circuit rotor
C. double cage rotor
B. wound rotor
D. none of the above