This set of Network Theory Multiple Choice Questions & Answers (MCQs) focuses on “Voltage, Current and Power in a Star Connected System”.
1. In star connected system, VRY is equal to?
a) VYR
b) -VYR
c) 2VYR
d) 3VYR
View Answer
Explanation: The voltage available between any pair of terminals is called the line voltage. The double script notation is purposefully used to represent voltages and currents in poly phase circuits. In star connected system, VRY = – VYR.
2. In three phase system, the line voltage VRY is equal to?
a) phasor sum of VRN and VNY
b) phasor difference of VRN and VNY
c) phasor sum of VRN and VNY
d) algebraic sum of VRN and VNY
View Answer
Explanation: In three phase system, the line voltage VRY is equal to the phasor sum of VRN and VNY which is also equal to the phasor difference of VRN and VYN.
3. The relation between the lengths of the phasors VRN and – VYN is?
a) |VRN| > – |VYN|
b) |VRN| < – |VYN|
c) |VRN| = – |VYN|
d) |VRN| >= – |VYN|
View Answer
Explanation: The voltage VRY is found by compounding VRN and VYN reversed. The relation between the lengths of the phasors VRN and – VYN is |VRN| = – |VYN|.
4. In a star connected system, the phasors VRN, VYN are ____ apart.
a) 15⁰
b) 30⁰
c) 45⁰
d) 60⁰
View Answer
Explanation: In a star connected system, the phasors VRN, VYN are separated by θ = 60⁰. To subtract VYN from VRN, we reverse the phase VYN and find its phasor sum with VRN.
5. The relation between VRY, Vph in a star connected system is?
a) VRY = Vph
b) VRY = √3Vph
c) VRY = 3√3Vph
d) VRY = 3Vph
View Answer
Explanation: The two phasors VYN and VBN are equal in length and are 60⁰apart. The relation between VRY, Vph in a star connected system is VRY = √3Vph.
6. In a star connected system, the relation between VYB, Vph is?
a) VYB = Vph
b) VYB = 3√3Vph
c) VYB = 3Vph
d) VYB = √3Vph
View Answer
Explanation: In a star connected system, the relation between VYB, Vph is VYB = √3Vph. The line voltage VYB is equal to the phasor difference of VYN and VBN and is equal to √3Vph.
7. The voltages, VBR ,Vph are related in star connected system is?
a) VBR = 3Vph
b) VBR = 3√3Vph
c) VBR = √3Vph
d) VBR = Vph
View Answer
Explanation: The voltages, VBR, Vph in star connected system are related as VBR = √3Vph. The line voltage VYB is equal to the phasor difference of VBN and VRN and is equal to √3Vph.
8. A symmetrical star connected system has VRN = 230∠0⁰. The phase sequence is RYB. Find VRY.
a) 398.37∠30⁰
b) 398.37∠-30⁰
c) 398.37∠90⁰
d) 398.37∠-90⁰
View Answer
Explanation: Since the system is a balanced system, all the phase voltages are equal in magnitude but displaced by 120⁰. VRN = 230∠0⁰V. VRY = √3×230∠(0o+30o)V=398.37∠30oV.
9. A symmetrical star connected system has VRN = 230∠0⁰. The phase sequence is RYB. Find VYB.
a) 398.37∠-30⁰
b) 398.37∠210⁰
c) 398.37∠90⁰
d) 398.37∠-90⁰
View Answer
Explanation: Corresponding line voltages are equal to √3 times the phase voltages and are 30⁰ ahead of the respective phase voltages. VYN = 230∠-120⁰V. VYB = √3×230∠(-120o+30o)V=398.37∠-90⁰V.
10. A symmetrical star connected system has VRN = 230∠0⁰. The phase sequence is RYB. Find VBR.
a) 398.37∠210⁰
b) 398.37∠-210⁰
c) 398.37∠120⁰
d) 398.37∠-120⁰
View Answer
Explanation: All the line voltages are equal in magnitude and are displaced by 120⁰. VBN = 230∠-240⁰V. VBR = √3×230∠(-240o+30o)V=398.37∠-210oV.
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