"Jerry" wrote in message
oups.com...

# Fred # wrote:
What is your source for the cable impedance R+jX values? Do you use a
default power factor or is it user defined?

The voltage drop calculator uses the equation:
vd=2*K*L*I/CMA
Where K = 12.9 for copper and 21.2 for Aluminum
K is the resistance in ohms of one foot of a one mil conductor at 75
degrees C.
L is one way distance from supply to load in feet
I is current in amperes
CMA is circular mil area of conductor
vd is voltage drop in volts
This is a a very conservative calculation since the load is assumed to
be the same as the OCPD value and the conductor is assumed to be at 75
degrees C.
This is the standard method of calculating voltage drop used by
electricians for the last 50 years and appears in journeyman
electrician tests for several states.
Using the impedance method and knowing the precise load can be more
accurate, but voltage drop is a best guess for the most part anyway.

The more exact formula incorporating impedance and power factor is no more
complicated than the above equation but the system power factor maybe a
little tricky to get - measurement, calculation or assumption. When
conductors get larger, the Z (impedance) will be significantly larger than
the R (dc resistance) so you expect a significant different between the
equations that incorporate only R values and equation with Z values. The
different in voltage drop is even more so between a 60Hz system and a 400Hz
system like an aircraft generator.

At the $300 million Healy Power Plant Job in Alaska the engineers
simply specified 460 volt motors to be used on a 480 volt system and
that solved all their voltage drop problems.


You mean 460V synchronous motors?