# Network Theory Questions and Answers – Voltage, Current and Power in a Star Connected System

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

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

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|

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

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

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

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

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

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

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

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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