Introduction to Electrical Power and Power Electronics

49Common Aspects of Power Equipment

VV

IR IX IX IR

sL

OA AB

222

2

=+=+×+×

()

+× −×cossin (cos sθθ θ iin )θ

2

.

(2.14)

For typical pf around 0.85, we can approximately write the source voltage V

s

=

OB= OA and, subsequently, the voltage drop magnitude:

V

drop

= V

s

– V

L

= OA – V

L

= I × R cos θ + I × X sin θ = I × (R cos θ + X sin θ). (2.15)

We can take the following as the effective impedance between the source and the

load:

Z

eff

= R cos θ + X sin θ (2.16)

which, when multiplied with current I, gives the voltage drop by simply applying

Ohm’s law:

V

drop

= I × Z

eff

. (2.17)

All calculations are done using volts, amperes, and ohms per phase and taking θ

positi ...