MSBTE I Scheme Practice MCQs of “Element
of Electrical Engineering (22215)”
UNIT-3. Polyphase AC Circuits.
Q1. Power in a Three
Phase Circuit = _________.
1. P = 3 VPh IPh CosФ
2. P = √3 VL IL CosФ
3. Both 1 & 2.
4. None of The Above
Answer: (3)…Both 1 & 2.
Q2. A polyphase system is
generated by______?
1. Having two or more
generator windings separated by equal electrical angle.
2. Having generator
windings at equal distances
3. None of the above
4. A and C
Answer: 1. Having two or
more generator windings separated by equal electrical angle.
Q3. In a three phase AC
circuit, the sum of all three generated voltages is _______ ?
1. Infinite (∞)
2. Zero (0)
3. One (1)
4. None of the above
Answer: 2. Zero (0)
Q4. For a star connected
three phase AC circuit ———
1. Phase voltage is equal
to line voltage and phase current is three times the line current
2. Phase voltage is square
root three times line voltage and phase current is equal to line current
3. Phase voltage is equal
to line voltage and line current is equal to phase current
4. None of the above
Answer: 2. Phase voltage is square root three times line
voltage and phase current is equal to line current
Q5. In a three phase,
delta connection ——-
1. line current is equal
to phase current
2. Line voltage is equal
to phase voltage
3. None of the above
4. Line voltage and line
current is zero
Answer: 2. Line voltage is equal to phase voltage
Q6. For a star connection
network, consuming power of 1.8kW and power factor 0.5, the inductance and
resistance of each coil at a supply voltage of 230 Volts, 60 Hz is ______?
1. 0.1H,
8 Ohms
2. 0.5H,
10 Ohms
3. 0.3H,
7.4 Ohms
4. 1H,
7 Ohms
Answer: 3. 03H, 7.4 Ohms
Q7. For a three-phase
delta connected load, fed from a star connected network, the power transferred
to the load is _____?Star to Delta & Delta to Star MCQs
1. 3 kW
2. 4.7 kW
3. 5 kW
4. 7 kW
Answer: 2. 4.7 kW
Q8. In a three phase AC
circuit, power is measured using a Wattmeter.
1. True
2. False
Answer: 1. True
Q9. For a polyphase
system, the number of Wattmeter required to measure power is equal to ——
1. Number
of wires
2. One
less than number of wires
3. Number
of phases
4. None
of the above
Answer: 2. One less than number of wires
Q10. For the below star connected network of equal
resistances, if the Wattmeter reading is 5kW and ammeter reading is 25 Amperes,
the power factor, resistance and inductance are __________ respectively.wattmeter star delta mcqs 5kw
resistor inductor capacitance
1. 1.5
Ohms, 0.1H
2. 0.866,
8 Ohms, 0.02H
3. 5.10
Ohms, 0.01H
4. Ohms,
0.02H
Answer: 2. 0.866, 8 Ohms, 0.02H
Q11. For a three phase,
three wire system, the two Wattmeter read 4000 Watts and 2000 Watts
respectively. The power factor when both meters give direct reading is _______
?
1. 1
2. 0.5
3. 0.866
4. 0.6
Answer: 3. 0.866
Q12. For a balanced three
phase, three wire system with input power of 10kW, at 0.9 power factor, the
readings on both wattmeter are ————– respectively
1. 7kW,
3kW
2. 6350W,
3650W
3. 5000W,
5000W
4. 7600W,
1200W
Answer: 2. 6350W, 3650W
Q13. A polyphase system is generated by——-
1. Having
two or more generator windings separated by equal electrical angle.
2. Having
generator windings at equal distances
3. None
of the above
4. A
and C
Answer: ( 1 )
Q14. In a three phase AC circuit, the sum of all
three generated voltages is ————
1. Infinite
2. Zero
3. One
4. None
of the above
Answer: ( 2 )
Q15. For a star connected three phase AC circuit
———
1. Phase
voltage is equal to line voltage and phase current is three times the line
current
2. Phase
voltage is square root three times line voltage and phase current is equal to
line current
3. Phase
voltage is equal to line voltage and line current is equal to phase current
4. None
of the above
Answer: ( 2 )
Q16. In a three phase, delta connection ——-
1. line
current is equal to phase current
2. Line
voltage is equal to phase voltage
3. None
of the above
4. Line
voltage and line current is zero
Answer: ( 2 )
Q17. For a star connection network, consuming
power of 1.8kW and power factor 0.5, the inductance and resistance of each coil
at a supply voltage of 230 Volts, 60 Hz is ——-
1. 0.01H,
8 Ohms
2. 0.05H,
10 Ohms
3. 0.03H,
7.4 Ohms
4. 1H,
7 Ohms
Answer: ( 3 )
Q18. For a three-phase delta connected load, fed
from a star connected network, the power transferred to the load is_phase delta
connected load fed from star connected network
1. 3
KW
2. 7
KW
3. 5
KW
4. 7KW
Answer: ( 2 )
Q19. In a three phase AC circuit, power is
measured using a Wattmeter.
1. True
2. False
Answer: ( 1 )
Q20. For a polyphase
system, the number of Wattmeter required to measure power is equal to ——
1. Number
of wires
2. One
less than number of wires
3. Number
of phases
4. None
of the above
Explanatory Answer:
The number of Wattmeter
required to measure power in a polyphase system is determined using Blondell’s
theorem. According to this, the number of Wattmeter required is equal to one
less than the number of wires in the circuit. For example, in a three phase,
four wire system (Star network), the number of Wattmeter required is three.
Q21. For the below star connected network of equal
resistances, if the Wattmeter reading is 5kW and ammeter reading is 25 Amperes,
the power factor, resistance and inductanceis ————respectively star connected
network of equal resistances
1. 1,
5 Ohms, 0.1H
2. 0.866,
8 Ohms, 0.02H
3. 0.5,
10 Ohms, 0.01H
4. 0.4,
8 Ohms, 0.02H
Therefore, Inductance, L
= 0.02H
Q22. For a three phase, three wire system, the two
Wattmeter read 4000 Watts and 2000 Watts respectively. The power factor when
both meters give direct reading is———–
1. 1
2. 0.5
3. 0.866
4. 0.6
Answer: ( 3 )
Q23. For a balanced three phase, three wire system
with input power of 10kW, at 0.9 power factor, the readings on both wattmeter
are ————– respectively
1. 7kW,
3kW
2. 6350W,
3650W
3. 5000W,
5000W
4. 7600W,
1200W
Answer: ( 2 )
Q24. In a three-phase Induction motor the
electrical energy supplied to the stator windings is converted to mechanical
energy in form of rotating rotor windings
1. True
2. False
Answer: ( 1 )
Q25. The name of the Induction motor comes from
the fact that——-
1. Operation
of the motor depends upon the induced voltage in the stator
2. Operation
of the motor depends upon the value of coil windings
3. Operation
of the motor depends upon the induced voltage in the rotor conductors
4. None
of these
Answer: ( 3 )
Q26. An induction motor is ———
1. Self-starting
2. Requires
external supply
3. A
or C
4. None
of these
Answer: ( 1 )
Q27. Slip of an induction motor lies between ——-
1. 0
to 10 %
2. 0
to 400 RPM
3. 0
to 5 %
4. 0
to 4000 RPM
Answer: ( 3 )
Q28. In a three-phase induction motor, frequency
of the rotor current is ——
1. Equal
to the supply frequency
2. Proportional
to the slip and supply frequency
3. Equal
to the one less than supply frequency
4. Equal
to the synchronous speed
Answer: ( 2 )
Q29. In a squirrel cage induction motor, the rotor
slots are——
1. Placed
in line with the rotor shaft
2. Skewed
at a certain angle to the rotor shaft
3. Parallel
to the rotor shaft
4. None
of these
Answer: ( 2 )
Q30. In a slip ring induction motor, external
resistors are connected in the rotor circuit
1. True
2. False
Answer: ( 1 )
Q31. Rotor induced EMF is nearly———–of maximum
value
1. 5%
2. 20%
3. 15%
4. 10%
Answer: ( 2 )
Q32. The torque – slip characteristics for an
Induction motor is a curve because
1. For
small values of slip, torque is directly proportional
2. For
larger values of slip, torque is inversely proportional
3. Both
a and c
4. None
of these
Answer: ( 3 )
Q33. For an 8-pole induction motor supplied with
power by a 6 pole Alternator at 1200 revolutions per minute, the value of motor
speed at slip of 3% is –
1. 800
RPM
2. 400
RPM
3. 873
RPM
4. 900
RPM
873 RPM.
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