Page 98 - Electric Machinery Fundamentals

7 4 ELECTRIC MACHINERY FUNDAMENTALS

I line 0.18,0 jO.24 n
+ P d
loa
ZEne
+
\L
V lood (I'---r--" Z lood
4+j3D

(al
TI I line 0.18 n jO.24 n
: 10 J"AA
leI vvv
• • Zlinc
+

(

V=480LOoV
(bl
FIGURE 2-6
The power system of Example 2-1 (a) without and (b) with transformers at the ends ofthe
transmission line.

(b) Suppose a 1:10 step-up transformer is placed at the generator end of the trans-
mission line and a 10:1 step-down transformer is placed at the load end of the
line (as shown in Figure 2-6b). What will the load voltage be now? What will
the transmission line losses be now?

Solution
(a) Figure 2-6a shows the power system without transformers. Here I e = I line =
I]oau' The line current in this system is given by
V
Ilinc = Z Z
linc + load

(0.1811 + jO.24!1) + (411 + j3 11)
480 L O° 480 LO°
4.18 + j3.24 5.29 L37.8°
~ 90.8L - 37.8° A
Therefore the load voltage is

~ (90.8L - 37.8' A)(411 + j311)
~ (90.8 L - 37.8' A)(5 L36.9° !1)
I
~ 454 L - 0.9 V
0