Question

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

The question was posed to me in an online interview.

My enquiry is from Three-Phase Unbalanced Circuits topic in portion Polyphase Circuits of Network Theory

Answer 1

Correct answer is (d) (-34.64-j20) A

Explanation: The voltage VBR is VBR = 400∠-240⁰V. The impedance Z3 is Z3 = 10∠-90⁰Ω => IB = (400∠240^o)/(10∠-90^o)=(-34.64-j20)A.