250+ TOP MCQs on Voltage, Current and Power in a Star Connected System and Answers

Network Theory Multiple Choice Questions on “Voltage, Current and Power in a Star Connected System”.

1. In star connected system, V_RY is equal to?
A. V_YR
B. -V_YR
C. 2V_YR
D. 3V_YR

Answer: B
Clarification: 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, V_RY = – V_YR.

2. In three phase system, the line voltage V_RY is equal to?
A. phasor sum of V_RN and V_NY
B. phasor difference of V_RN and V_NY
C. phasor sum of V_RN and V_NY
D. algebraic sum of V_RN and V_NY

Answer: A
Clarification: In three phase system, the line voltage V_RY is equal to the phasor sum of V_RN and V_NY which is also equal to the phasor difference of V_RN and V_YN.

3. The relation between the lengths of the phasors V_RN and – V_YN is?
A. |V_RN| > – |V_YN|
B. |V_RN| < – |V_YN|
C. |V_RN| = – |V_YN|
D. |V_RN| >= – |V_YN|

Answer: C
Clarification: The voltage V_RY is found by compounding V_RN and V_YN reversed. The relation between the lengths of the phasors V_RN and – V_YN is |V_RN| = – |V_YN|.

4. In a star connected system, the phasors V_RN, V_YN are ____ apart.
A. 15⁰
B. 30⁰
C. 45⁰
D. 60⁰

Answer: D
Clarification: In a star connected system, the phasors V_RN, V_YN are separated by θ = 60⁰. To subtract V_YN from V_RN, we reverse the phase V_YN and find its phasor sum with V_RN.

5. The relation between V_RY, Vph in a star connected system is?
A. V_RY = V_ph
B. V_RY = √3V_ph
C. V_RY = 3√3V_ph
D. V_RY = 3V_ph

Answer: B
Clarification: The two phasors V_YN and V_BN are equal in length and are 60⁰apart. The relation between V_RY, V_ph in a star connected system is V_RY = √3V_ph.

6. In a star connected system, the relation between V_YB, V_ph is?
A. V_YB = V_ph
B. V_YB = 3√3V_ph
C. V_YB = 3V_ph
D. V_YB = √3V_ph

Answer: D
Clarification: In a star connected system, the relation between V_YB, V_ph is V_YB = √3V_ph. The line voltage V_YB is equal to the phasor difference of V_YN and V_BN and is equal to √3V_ph.

7. The voltages, V_BR ,V_ph are related in star connected system is?
A. V_BR = 3V_ph
B. V_BR = 3√3V_ph
C. V_BR = √3V_ph
D. V_BR = V_ph

Answer: C
Clarification: The voltages, V_BR, V_ph in star connected system are related as V_BR = √3V_ph. The line voltage V_YB is equal to the phasor difference of V_BN and V_RN and is equal to √3V_ph.

8. A symmetrical star connected system has V_RN = 230∠0⁰. The phase sequence is RYB. Find V_RY.

A. 398.37∠30⁰
B. 398.37∠-30⁰
C. 398.37∠90⁰
D. 398.37∠-90⁰

Answer: A
Clarification: Since the system is a balanced system, all the phase voltages are equal in magnitude but displaced by 120⁰. V_RN = 230∠0⁰V. V_RY = √3×230∠(0^o+30^o)V=398.37∠30^oV.

9. A symmetrical star connected system has V_RN = 230∠0⁰. The phase sequence is RYB. Find V_YB.

A. 398.37∠-30⁰
B. 398.37∠210⁰
C. 398.37∠90⁰
D. 398.37∠-90⁰

Answer: D
Clarification: Corresponding line voltages are equal to √3 times the phase voltages and are 30⁰ ahead of the respective phase voltages. V_YN = 230∠-120⁰V. V_YB = √3×230∠(-120^o+30^o)V=398.37∠-90⁰V.

10. A symmetrical star connected system has V_RN = 230∠0⁰. The phase sequence is RYB. Find V_BR.

A. 398.37∠210⁰
B. 398.37∠-210⁰
C. 398.37∠120⁰
D. 398.37∠-120⁰

Answer: B
Clarification: All the line voltages are equal in magnitude and are displaced by 120⁰. V_BN = 230∠-240⁰V. V_BR = √3×230∠(-240^o+30^o)V=398.37∠-210^oV.