Power System Analysis And Design SI Edition 6Th Edition By Glover - Test Bank

Quiz 1

ECE 476

Two balanced three-phase loads are in parallel.

a. b. Load 1 draws 10 kW at 0.8 PF lagging

Load 2 draws 20 kVA at 0.6 PF leading

The loads are supplied by a balanced three-phase 480 VLL source.

(a) Draw the power triangle for the combined load.

PL = P1 + P2 = 22 kW

21.12°

QL = Q1 + Q2

= -8.5 kVAR

SL = 23.59

kVA

(b) Determine PF of the combined load.

cos21.12° = 0.933 leading

(c) Determine the magnitude of the line current from the source.

𝑆𝐿

=

23.59×103

= 28.37 𝐴

𝐼𝐿 =

√3𝑉𝐿𝐿

√3×480

(d) Y-connected inductors are now installed in parallel with the combined load. What value of

inductive reactance is needed in each leg of the Y to make the source power factor unity?

3(𝑉𝐿𝑁)2

𝑄𝐼𝑛𝑑 = |𝑄𝐿| = 8.5 × 103 𝑉𝐴𝑅 =

3(480/√3)2

𝑋Y =

= 27.1 Ω