Why do transmission lines carry such high voltages?

Line Construction is a Big Ecological Footprint!

Consider the following hypothetical (and non-physical) situation:

How to solve the loss problem:

Current = Power/Voltage; If we increase V by a factor of 10, then I lowers by a factor of 10 (at constant power) and the power dissipated as heat lowers by a factor of 102.

Hence if we increase 120 Volts to 1200 Volts we have only 69.4 watts of energy loss and a 99% energy efficient delivery system This is why high voltage (typically 115-230 thousand Volts or kiloVolts) transmission lines are required to delivery electricity from central generating sources (e.g. a hydroelectric dam) to consumers/grids hundreds of miles away.

But you don't want 115 KV coming into your house:

To step down the Voltage Use a Transformer

A transformer uses alternating current in one coil to induce alternating current in another. The induced voltage is given by: Vout = Vin x N2/N1 where N1 = Number of coils in the Primary and N2= Number of coils in the secondary. When N2 is less than N1, we reduce Vout. This is why there are transformers on power lines to step the voltage down to 120 Volts by the time it reaches your house.

Energy conservation tells us that Power In = Power Out

so

Vout x Iout = Vin x Iin

Since Vin is very high, Iin is low and (to prevent transmission loss); when Vin is stepped down to produce Vout (what you get at your house), Iout increases so you can run your stuff.

This is why a typical electricity substation is large:

The substation in my neighborhood.




Distrubution of Power Plants in the US
All have to be grid connected

Google Earth Emissions Tool

The economics of power transmission why the move to 765 KV has serious cost reductions and reduced losses.

So what's the problem.

Higher voltage means stronger localized electromagentic fields (EMF) which would adversely affect local biology - if there is any. Currently the most at risk population would be bats.

Note, 765 KV lines do exist already in the world and in some parts of the US.

The proposal is to build the equivalent of the interstate highway system with KV transmission because a) its cost effective and b) its needed to export wind and solar based electricity from remote areas.