Why do transmission lines carry such high voltages?
Line Construction is a Big Ecological Footprint!
Consider the following hypothetical (and non-physical) situation:
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:
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. |
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Energy conservation tells us that Power In = Power Out
so
This is why a typical electricity substation is large:
The substation in my neighborhood.
So what's the problem. /font>
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.