Handbook of Electrical Engineering

562 HANDBOOK OF ELECTRICAL ENGINEERING

Convert to system base values.

SWBD load kVA=Sog=

SWBD load power

SWBD load power factor

=

Pog

cosφog

=

900 × 1000

0. 9

= 1000 × 103 VA

SWBD load kVA/phase=Sogp=

1000 × 1000

3

= 333 × 103 VA

SWBD load power/phase=Pogp=

900 × 1000

3

= 300 × 103 VA

SWBD load reactive power/phase=Qogp=

√

(Sogp^2 −Sogp^2 )

= 145. 29 × 103 VAr

Ohmic resistance per phase=Rogp=

(

Phase voltage

Phase active power

) 2

=

(

Vog

Pogp

) 2

=

13 , 800 × 13 , 800

3 × 300 × 103

× 106

= 211 .6 ohms per phase

Ohmic reactance per phase=Xogp=

(

Phase voltage

Phase reactive power

) 2

=

(

Vog

Qogp

) 2

=

13 , 800 × 13 , 800

3 × 145. 29 × 103

× 106

= 436 .92 ohms per phase

Convert to the system base impedance values.

System impedance in per-unit=Ohmic impedance=

(load base kVA) (system base kVA)

(system base voltage)^2 (load base kVA)

Hence

Rog=

( 211. 6 × 1000 × 1000 )( 3125 × 1000 )

( 13 , 800 )^2 ( 1000 × 1000 )

= 3 .4722 pu

And

Xog=

( 436. 92 × 1000 × 1000 )( 3125 × 1000 )

( 13 , 800 )^2 ( 1000 × 1000 )

= 7 .1696 pu

These are the parallel elements of the load in per-unit at the system base.

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