Page 569 - Handbook of Electrical Engineering

562 HANDBOOK OF ELECTRICAL ENGINEERING

Convert to system base values.

SWBD load power
SWBD load kVA = S og =
SWBD load power factor
900 × 1000
P og 3
= = = 1000 × 10 VA
cos φ og 0.9
1000 × 1000 3
SWBD load kVA/phase = S ogp = = 333 × 10 VA
3
900 × 1000 3
SWBD load power/phase = P ogp = = 300 × 10 VA
3
√ 2 2
SWBD load reactive power/phase = Q ogp = (S ogp − S ogp )
3
= 145.29 × 10 VAr
2

Phase voltage
Ohmic resistance per phase = R ogp =
Phase active power
2

V og 13, 800 × 13, 800 6
= = × 10
P ogp 3 × 300 × 10 3
= 211.6 ohms per phase
Phase voltage
2
Ohmic reactance per phase = X ogp =
Phase reactive power
2
V og 13, 800 × 13, 800 6
= = 3 × 10
Q ogp 3 × 145.29 × 10
= 436.92 ohms per phase

Convert to the system base impedance values.

(load base kVA) (system base kVA)
System impedance in per-unit = Ohmic impedance = 2
(system base voltage) (load base kVA)

Hence
(211.6 × 1000 × 1000)(3125 × 1000)
R og = = 3.4722 pu
2
(13, 800) (1000 × 1000)

And
(436.92 × 1000 × 1000)(3125 × 1000)
X og = = 7.1696 pu
2
(13, 800) (1000 × 1000)
These are the parallel elements of the load in per-unit at the system base.

e) Motor control centre (MCC) parallel circuit components.