Re: electrical power

[Brian Whatcott <inet@INTELLISYS.NET>]

At 01:27 PM 2/20/02, Justin wrote:
> Does anyone have any notes written about the distinction between P=VI and
> P=I^2R?  I understand that the latter refers to "joule heating loss" but I
> don't feel clear as to why.
>
> Justin Parke

People in the public utilities can be leary about regarding the product of
volts and amps as power - they are only too familiar with the way current
usually trails the voltage wave that they supply - in part due to the many
motors which we find so
useful. So they talk about volt.amps which is in some ways more meaningful
to them:
they need to size conductors for peak currents, and they need to size
insulating sheaths and pendants for maximum volts. It is for this reason
that you may find  industrial  users can be charged in some circumstances
for the volt-amps they have extracted from their lines rather than the watts.

The utilities are aware that 5 to 10% of their resource is expended in
heating transmission lines en route to your house. They think of these
losses as I squared R losses.
They would much prefer to reduce this waste by reducing the transmission
current, than by reducing the line resistance; and of course one way to
achieve this end is by up transforming the transmission voltage to provide
similar power at reduced current.

Brian W


Brian Whatcott
  Altus OK                      Eureka!