# 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 Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Determine the phase current I_{R}.

a) (17.32-j10) A

b) (-17.32-j10) A

c) (17.32+j10) A

d) (-17.32+j10) A

2. The three impedances Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the phase current I_{Y}.

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 Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the phase current I_{B}.

a) (34.64-j20) A

b) (34.64+j20) A

c) (-34.64+j20) A

d) (-34.64-j20) A

5. The three impedances Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the line current I_{2}.

a) (-27.32+j10) A

b) (27.32+j10) A

c) (-27.32-j10) A

d) (27.32-j10) A

6. The three impedances Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 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 Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the line current I_{1}.

a) (-51.96-j10) A

b) (-51.96+j10) A

c) (51.96+j10) A

d) (51.96+j10) A

8. The three impedances Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 10∠-90⁰Ω are delta-connected to a 400V, 3 – Ø system. Find the line current I_{3}.

a) (24.646+j20) A

b) (-24.646+j20) A

c) (-24.646-j20) A

d) (24.646-j20) A

9. The three impedances Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 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 Z_{1} = 20∠30⁰Ω, Z_{2} = 40∠60⁰Ω, Z_{3} = 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

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