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Re: [Phys-L] Power loss in transmission lines

• From: John Denker <jsd@av8n.com>
• Date: Fri, 23 May 2014 02:11:25 -0700

On 05/23/2014 01:38 AM, Savinainen Antti wrote:
http://www.bsharp.org/physics/transmission

What bothers me is that the loss fraction can conceivably be one or
even more, which is clearly not physical. Perhaps I am missing
something?

Starting from the formula

Ploss / P = P R / V²
= fractional loss

rewrite it as

Ploss / P = ΔV / V

which I find simpler to write, simpler to interpret, and in
all ways better.

So the fractional loss cannot be greater than unity ...

To say the same thing the other way, you could have the
fractional loss exceed unity if the load is actively sucking
power out of the system. This *is* physically possible,
although I suppose it depends somewhat on what you define
as "the" voltage V and what you define as "the" load as
opposed to the source.

Higher-than-expected fractional loss is not even particularly
uncommon if you have a two-phase or three-phase AC power
distribution scheme, in situations where the symmetry is
broken by a higher-than-expected resistance in /one/ leg
of the distribution circuit.

Another common way this can happen is if you hook a
battery charger up to the battery /backwards/.