Page 414 - Power Electronic Control in Electrical Systems

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Power electronic control in electrical systems 393
p p 2 p 2 p 2
(ii) (a) I L(rms) ˆ [(3 12:5) ‡ 0 ‡ (3 4:5) ‡ (3 3:0) ]
p
ˆ [468:75 ‡ 0 ‡ 60:75 ‡ 27:0]
ˆ 23:59A(rms)
p 2 2 2
(b) V L(rms) ˆ [220 ‡ 19:0 ‡ 15:0 ]
ˆ 221:33 V(rms)
(c) P ˆ 3 [220 12:5 cos 15:0 ‡ 19:0 4:5cos 21:0

‡ 15:0 6:0 cos ( 26:0 )]

ˆ 2656:30 ‡ 79:82 ‡ 80:89
ˆ 2817:00 W p
2
2
(d) Cable loss ratio ˆ I 2 /I 2 ˆ 23:59 /( 3 12:5) ˆ 1:187
L(rms) 1(rms)
20. (i) Draw the EMF phasor diagram for a Yd1 transformer. Also draw the
configuration of the primary and secondary windings on a three-limb core.
Include all internal connections and correct terminal labels.
(ii) A 230/66-kV Yd1 transformer gave the following test results:

Test Line Current, A Power factor Condition
Open circuit 20 0.45 HV winding open
25% voltage on LV winding
Short circuit 120 0.08 LV winding shorted
2% voltage on HV winding

Draw an equivalent circuit for one phase and calculate the series impedance Z se ˆ
R e ‡ jX e and shunt admittance Y sh ˆ 1/R c ‡ 1/jX m , both referred to the HV side.

(i)

Fig. 9.14

(ii)

Fig. 9.15