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

Timothy had the decisive insight. So Antti would be better served by the loss fraction given in this way:
(Power Lost) / (Power Lost plus Power Delivered) - a fraction which never exceeds nor even equals one.

Brian Whatcott Altus OK Indian Territory.

On 5/23/2014 6:42 AM, Folkerts, Timothy J wrote:
The "loss fraction" on the page you mention is the ratio of
(power lost) / (power delivered)

It was not
(power lost) / (power generated).

So if you generate 1 kWh and 0.1 kWh is delivered and 0.9 kWh are lost, you could either say that 90% of the original power is lost (always between 0-1), or that 9 times as much power is lost as delivered (between 0 and infinity). These are two ways of saying the same thing.

Tim
________________________________________
From: Phys-l [phys-l-bounces@phys-l.org] on behalf of Savinainen Antti [antti.savinainen@kuopio.fi]
Sent: Friday, May 23, 2014 3:38 AM
To: phys-l@phys-l.org
Subject: [Phys-L] Power loss in transmission lines

Hi,

I suppose that the power loss in transmission lines is part of most intro courses on E&M. The basic idea is quite clear: given a certain produced power, the greater the voltage the smaller the current is, which means the smaller power loss in the transmission lines. So far so good. We had a simple quantitative calculation on the power loss and I casually asked my students check the case when the voltage is pretty low. This gave a nonsensical answer. I looked at the situation,and quickly derived a formula of the loss fraction. The same formula can be found here: <http://www.bsharp.org/physics/transmission> (Scroll down to the section "High-Voltage Transmission Lines").

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?

Regards,

Antti
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