Three-Phase Unbalanced Circuits MCQ’s

This set of Network Theory Multiple Choice Questions & Answers (MCQs) focuses on “Three-Phase Unbalanced Circuits”.

1. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Determine the phase current IR.
a) (17.32-j10) A
b) (-17.32-j10) A
c) (17.32+j10) A
d) (-17.32+j10) A

2. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the phase current IY.
a) (10-j0) A
b) (10+j0) A
c) (-10+j0) A
d) (-10-j0) A

3. If the system is a three-wire system, the currents flowing towards the load in the three lines must add to ___ at any given instant.
a) 1
b) 2
c) 3
d) zero

4. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the phase current IB.
a) (34.64-j20) A
b) (34.64+j20) A
c) (-34.64+j20) A
d) (-34.64-j20) A

5. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the line current I2.
a) (-27.32+j10) A
b) (27.32+j10) A
c) (-27.32-j10) A
d) (27.32-j10) A

6. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the power in the R phase.
a) 6628
b) 6728
c) 6828
d) 6928

7. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the line current I1.
a) (-51.96-j10) A
b) (-51.96+j10) A
c) (51.96+j10) A
d) (51.96+j10) A

8. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the line current I3.
a) (24.646+j20) A
b) (-24.646+j20) A
c) (-24.646-j20) A
d) (24.646-j20) A

9. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the power in the Y phase.
a) 1000
b) 2000
c) 3000
d) 4000

10. The three impedances Z1 = 20∠30⁰Ω, Z2 = 40∠60⁰Ω, Z3 = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the power in the B phase.
a) 0
b) 1
c) 3
d) 2