Page 35 - Solutions Manual to accompany Electric Machinery Fundamentals

Z line  3 4 j 



 V 480 0 V Z  30  j 40 
S load

The load current in this system is

480 0 V

I load   j 3   4  30 j 40     8.727   53.13 A
The load voltage is

 V 8.727  53.13 A 30  j 40   436.4 0 A  
load
The power consumed by the load is
  P 8.727 A 2  30    2285 W
load
The power consumed by the transmission line is
P line   8.727 A 2  3    228.5 W

The efficiency of the power system is

P P 2285 W
  OUT  100%  load  100%   100% 90.9%


P IN P load  P line 2285 W 228.5 W
(b) The equivalent circuit of this power system is shown below.
Z line  3 4 j 



 V 480 0 V 1:5 5:1 Z  30 j 40 
S load

The line impedance referred to primary side of T 1 is:
 2 2
Z line  a Z line   0.2  3  4 j   0.12  j 0.16 

The load impedance referred to primary side of T 1 is the same as the actual impedance, since the turns
ratios of the step-up and step-down transformers undo each other’s changes.

Z load  30  j 40 
The resulting equivalent circuit referred to the primary side of T 1 is:

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