Electrical Power Lines Use High Voltage Lines to Reduce Current

[SaintJude]

Electrical Power Lines Use High Voltage Lines to Minimize Power Loss.

I understand that in order to minimize power loss, the electric company will minimize the current since (P = I^2R) . However, I'm confused once I realize that this suggests voltage is inversely proportional to the current.

Is this always the case: is voltage always inversely proportional to current?

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[RemoteDoc]

Since when is voltage inversely proportional to current? V=IR or I=V/R Either way they are proportional. Where did you get the first statement. I know they also use Alternating Current, instead of Direct Current to eliminate power loss. This is because the Wire, has SOME resistance, and thus some power is lost to the surroundings. AC lessens the degree to this.

 

[milski]

For a constant power (whatever the powerplant produces) they are inversely proportional - P=IU. At that point increasing one and decreasing the other does not really matter - the final result is the same. There will always be some losses during the transportation. If R is the resistance of the powerlines, the loss is I^2R. It's a lot easier and cheaper to decrease I by increasing U than to work on decreasing R - that in general involves different materials and is harder and more expensive.

 

[SaintJude]

I was in high hopes that you would answer, milski. Thank you. So the voltage is proportional to the current , unless the power is constant. That actually makes sense.

 

[milski]

I was in high hopes that you would answer, milski. Thank you. So the voltage is proportional to the current , unless the power is constant. That actually makes sense.

That's a very strong statement - you'll be much better off if you specify exactly what you are changing or keeping constant. For a fixed resistance, the voltage and current will be proportional. For a constant power, the voltage and the current will be inversely proportional.

 

[chiddler]

http://forums.studentdoctor.net/showthread.php?t=898055

this took a long time for me to figure out initially :|

 

[kasho11]

For a fixed resistance, the voltage and current will be proportional. For a constant power, the voltage and the current will be inversely proportional.

Much more succinct and easily understandable now why they want a high V.

 

[SaintJude]

Yeah, I actually posted in that thread...oh my goodness. But I think I didn't really understand what was going on. If MedPr sees this, I apologize belatedly for giving a useless answer..

Anyway, what worries me is that in both cases (as in the AAMC6 question & the TBR question from the thread) the question stem did NOT state that power is constant!

The AAMC6 was worded a bit less ambiguously but still it just asked:

"Electrical power for transmission over long distances is "stepped up" to a very high voltage in order to"...."

 

[chiddler]

i guess. i spent so much time with this question the first time that i remembered that power is constant and got the question right.

plus it's the best answer, anyway. why would our power lines have high voltage unnecessarily if it just increased heat production?

 

[milski]

Well, it's sort of implied - a power station would have a limited capacity and the goal is to deliver all of it with maximum efficiency.