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

Network Theory MCQs on “Voltage, Current and Power in a Delta Connected System”.

1. In a delta connected system, the voltage across the terminals R and Y is 400∠0⁰. Calculate the line voltage V_RY. Assume R_RY phase sequence.
A. 400∠0⁰
B. 400∠120⁰
C. 400∠-120⁰
D. 400∠240⁰

Answer: A
Clarification: In a balanced delta-connected system we know |V_RY| = |V_Ph|, and it is displaced by 120⁰, therefore the line voltage V_RY is V_RY = 400∠0⁰V.

2. In a delta connected system, the voltage across the terminals R and Y is 400∠0⁰. Find the line voltage V_YB.
A. 400∠120⁰
B. 400∠-120⁰
C. 400∠240⁰
D. 400∠-240⁰

Answer: B
Clarification: As |V_YB| = |V_Ph|, and is displaced by 120⁰, therefore the line voltage V_YB is V_YB = 400∠-120⁰V. A balanced three phase, three wire, delta connected system is referred to as mesh connection because it forms a closed circuit.

3. In a delta connected system, the voltage across the terminals R and Y is 400∠0⁰. Find the line voltage V_BR.
A. 400∠240⁰
B. 400∠120⁰
C. 400∠-240⁰
D. 400∠-120⁰

Answer: C
Clarification: We know, |V_BR| = |V_Ph|, and is displaced by 120⁰, therefore the line voltage V_BR is V_BR = 400∠-240⁰V. Delta connection is so called because the three branches in the circuit can be arranged in the shape of delta.

4. In delta-connected system, the currents I_R, I_Y, I_B are equal in magnitude and they are displaced by _____ from one another.
A. 0⁰
B. 60⁰
C. 90⁰
D. 120⁰

Answer: D
Clarification: In delta-connected system, the currents I_R, I_Y, I_B are equal in magnitude and they are displaced by 120⁰ from one another. From the manner of interconnection of the three phases in the circuit, it may appear that the three phase are short circuited among themselves.

5. In a delta-connected system, the currents I_R = I_B = I_Y =?
A. I_Ph
B. 2I_Ph
C. 3I_Ph
D. 4I_Ph

Answer: A
Clarification: In a delta-connected system, the currents I_R = I_B = I_Y = I_Ph. Since the system is balanced, the sum of the three voltages round the closed mesh is zero; consequently no current can flow around the mesh when the terminals are open.

6. The relation between I_L and I_Ph is in a delta connected system is?
A. I_L = I_Ph
B. I_L = √3 I_Ph
C. I_L = 3 I_Ph
D. I_L = 3√3I_Ph

Answer: B
Clarification: The relation between I_L and I_Ph is in a delta connected system is I_L = √3 I_Ph. The arrows placed alongside the voltages of the three phases indicate that the terminals are positive during their positive half cycles.

7. The line currents are ________ behind respective phase currents in a delta connected system.
A. 120⁰
B. 90⁰
C. 60⁰
D. 30⁰

Answer: D
Clarification: In a delta connected system, all the line currents are equal in magnitude but displaced by 120⁰ from one another and the line currents are 30⁰ behind the respective phase currents.

8. In a delta connected system, the expression of power (P) is?
A. V_LI_Lcosφ W
B. √3 V_LI_Lcosφ W
C. 3V_LI_Lcosφ W
D. 3√3V_LI_Lcosφ W

Answer: B
Clarification: The total power in the delta circuit is the sum of the powers in the three phases. In a delta connected system, the expression of power (P) is P = √3V_LI_Lcosφ W.

9. A balanced delta-connected load of (2+j3) Ω per phase is connected to a balanced three-phase 440V supply. The phase current is 10A. Find the total active power.
A. 7.26W
B. 726W
C. 7260W
D. 72.6W

Answer: C
Clarification: Z_Ph = √(2²+3²) = 3.6∠56.3⁰Ω. cosφ = R_Ph/Z_Ph = 2/3.6 = 0.55. I_L = √3× I_Ph = 17.32A. Active power = √3 V_LI_Lcosφ = √3×440×17.32×0.55= 7259.78W.

10. A balanced delta-connected load of (2+j3) Ω per phase is connected to a balanced three-phase 440V supply. The phase current is 10A. Find the apparent power.
A. 10955.67 VAR
B. 10.95567 VAR
C. 109.5567 VAR
D. 1.095567 VAR

Answer: A
Clarification: Sinφ = 0.83. Reactive power = √3 V_LI_Lsinφ. V_L = 440V, I_L = 17.32A. On substituting we get reactive power = √3 x 440 x 17.32 = 10955.67 VAR.