
Common Aspects ofPower Equipment 65
impedances of the generator, transformer, and cable. The load draws current I at
lagging pf cosθ at the load terminal voltage V
Load
, which must be equal to the source
voltage V
source
minus the voltage drop I × Z in the series impedance. Therefore, the
source voltage, which is maintained constant, must be equal to
V
˜
Source
= V
˜
Load
+ I
˜
× (R + j X) (3.13)
The phasor diagram of Equation (3.13) is shown in Figure3.7(b), the trigonometry of
which gives the exact magnitude of the source voltage for any pf = cosθ,
V
S
2
= OA
2
+ AB
2
= (V
L
+ I × R cosθ + I × X sinθ)
2
+ (I × X cosθ – I × R sinθ)
2
(3.14)
For a typi ...