3 - Phase AC Circuits - Electrical Engineering (MCQ) questions and answers

1)   In a star connected system, the current flowing through the line is

a. Greater than the phase current
b. Equal to the phase current
c. Lesser than the phase current
d. None of these
Answer  Explanation 

ANSWER: Equal to the phase current

Explanation:
No explanation is available for this question!
2)   By using two wattmeter method, power can be measured in

a. 3 - phase, 2 - wire system
b. 3 - phase, 3 - wire system
c. 3 - phase, 4 - wire system
d. All of these
Answer  Explanation 

ANSWER: 3 - phase, 3 - wire system

Explanation:
No explanation is available for this question!
3)   In delta connected system, the potential difference between line outers is

a. Equal to the phase voltage
b. Greater than the phase voltage
c. Less than the phase voltage
d. None of these
Answer  Explanation 

ANSWER: Equal to the phase voltage

Explanation:
No explanation is available for this question!
4)   Commutator motors have

a. Absolutely uniform torque
b. Approximately uniform torque
c. Non - uniform torque
d. None of these
Answer  Explanation 

ANSWER: Non - uniform torque

Explanation:
No explanation is available for this question!
5)   In a 3 - phase star connected balanced induction motor, the line voltage is equal to the

a. 3 times the phase voltage
b. √3 times the phase voltage
c. 1/√3 times the phase voltage
d. 1/3 times the phase voltage
Answer  Explanation 

ANSWER: √3 times the phase voltage

Explanation:
No explanation is available for this question!
6)   Three - phase induction motor is more suitable than single - phase because

a. It is self starting
b. Better efficiency compared to single - phase
c. Better power factor compared to single - phase
d. All of these
Answer  Explanation 

ANSWER: All of these

Explanation:
No explanation is available for this question!
7)   In a balanced 3-phase system, if one of the two wattmeter’s reading is negative then the

a. Reading should be taken as it is
b. Reading should be taken after reversing the pressure coil
c. Reading should be taken after reversing the current coil
d. All of these
Answer  Explanation 

ANSWER: Reading should be taken after reversing the pressure coil

Explanation:
No explanation is available for this question!
8)   The two wattmeter method is applicable for

a. Only star connected system
b. Only delta connected system
c. Both star connected and delta connected system
d. None of these
Answer  Explanation 

ANSWER: Both star connected and delta connected system

Explanation:
No explanation is available for this question!
9)   The expression for total power output of a delta connected system in terms of phase voltage and current is given by

a. 3VpIpcos∅
b. √3VpIpcos∅
c. 1/√ 3VpIpcos∅
d. 1/3 x VpIpcos∅
Answer  Explanation 

ANSWER: 3VpIpcos∅

Explanation:
No explanation is available for this question!
10)   When windings of 3 - phase induction motor is rotated in a magnetic field, then the emf induced in each phase are of

a. Same magnitude but different frequency
b. Different magnitude but same frequency
c. Same magnitude and same frequency
d. Different magnitude and different frequency
Answer  Explanation 

ANSWER: Same magnitude and same frequency

Explanation:
No explanation is available for this question!

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