#### Comment Preferences

• ##### only if total power consumption goes up...(47+ / 0-)

In your equation, if voltage went up, current would actually go down to make the equation stay in balance.

The equation you need to consult is P=I*V

So, if the total power requirement goes up, the current will go up (regardless of the voltage). This is why power lines can sag on hot days when there is a lot of power being consumed.. a lot of current running through the lines, and heating up the lines...

Freedom isn't free. So quit whining and pay your taxes.

[ Parent ]

• ##### And more directly(14+ / 0-)

P = R* I^2

or

P = R / V ^2

which is what gives you the 6x decrease in power loss for a 2.5x increase in voltage (resistance of the cable is the same).

[ Parent ]

• ##### Actually, the second equation is:(6+ / 0-)

P = V^2 / R

and I'm not sure how you draw the conclusion you do.

The man who moves a mountain begins by moving away small stones. -Confucius

[ Parent ]

• ##### You're right(5+ / 0-)

I screwed up the 2nd equation, but it's important to realize which V you're talking about. When it comes to losses in the transmission line, the V is the voltage drop across the line (which will be lower at lower I), not the input voltage.

So, at higher voltage at constant delivered power, the current will be lower and the reduced power loss will go like the square of the decreased current.

[ Parent ]

• ##### Here's a link to a handy ohms law calculator(1+ / 0-)
Recommended by:
kyril

usually the square chart is shown as a circle, but all the formulas are correct.  There are also some 3 phase AC formulas that one might find useful.

http://www.angelfire.com/...

Google Ohm's Law Calculator to find more.

Republicans are like alligators. All mouth and no ears.

[ Parent ]

• ##### You also need to change the transformer at each(2+ / 0-)
Recommended by:
goodpractice, kyril

end of the powerline to both boost the voltage on the line, and to step it down to distribution useful voltages, like 13,800 line to line, 7200 line to neutral distribution lines and such.

The transformers in the switchyard also have to have sufficient distances between phases to handle the magnetic forces that are generated, so it isn't as easy as it may seem, just to boost voltage.  Before it can be done, there is also an arduous and fairly long term process to modify standards for cross country powerlines and towers before this kind of change can be implemented.  So the regulatory environment must also change as well as the crossbars.  Much study for wind and ice loading, capacitance, effects on power factor correction and a lot more needs to be done before changes can be made.

But I like the idea, and agree with the higher efficiency of high voltage long distance power transmission.

Republicans are like alligators. All mouth and no ears.

[ Parent ]

• ##### In general(2+ / 0-)
Recommended by:
kyril, Ohiodem1

our national grid is long overdue for an upgrade, and boosting long-haul interconnections is going to be a major part of any strategy that relies on localized renewable sources.

Seems like a good time to revist the 'standards' for high voltage transmission and make the needed changes to reduce transmission losses, especially if it can be done relatively cheaply.

[ Parent ]

• ##### This is not true!!! And I think a bit confusing...(18+ / 0-)
In your equation, if voltage went up, current would actually go down to make the equation stay in balance.
Actually, current would increase to meet Ohm's Law.

What Mindful Nature is confusing is the placement of the voltage and load (resistance) when applying ohm's law. Each household represents a load. The voltage at the house is still going to be the same! That's the key! People are most familiar with 120V lines in their house. Their house is still going to draw the same average current at the same 120V voltage. So even their power consumed will also be the same. And that makes sense! So what are we changing?

We are changing (boosting) the transmission voltage going to the house and inserting new transformers to step that larger transmission voltage back down to 120V at the load (home). So it's a more complex circuit than a single voltage, current and resistance. You can't apply V=I*R to anything more than a single, lumped-parameter resistance.

The transmission line itself can be modeled as a very, very small resistance. That's why it is used as a conductor! And any current flowing through the line will generate a very small voltage across that line segment. That is where V=I*R does apply directly to the transmission line. But the voltage across the transmission line that we are talking about is very small relative to the voltage being carried by the line in relation to overall circuit ground.

What is saved/reduced here is the amount of current required at the load end of distribution, specifically at the transformer. A higher voltage on the primary/transmission-line side of the transformer means less current is needed on that same side of the transformer for a fixed power load. The power load is determined by the secondary/household side. This is where P=V*I applies. So if P is fixed for the house (which it is), a larger voltage allows a proportionally smaller current.

So if the voltage on the transmission lines can be higher, the current needed in those same transmission lines to deliver the original amount of power to the homes is smaller. And with less current in the transmission lines, there is less loss. And with less loss, there is more overall efficiency.

I think. ;)

The man who moves a mountain begins by moving away small stones. -Confucius

[ Parent ]

• ##### Yeesh, I'll just come right out and say,(21+ / 0-)

I don't understand a lot of what you guys are talking about, but man do I love running across conversations like this on dkos. Cheers!

And my baby's my common sense, so don't feed me planned obsolescence.

[ Parent ]

• ##### Simple(9+ / 0-)

Power transmitted = Current * Voltage.

To transmit a given amount of power (what your wind farm produces), the higher the voltage you can transmit at, the lower the current.  Since the transmission wires have a resistance that depends on the size (cross section) and length of the cable, and is thus fixed, unless we rebuild the whole thing, the power lost in transmission because of the resistance of the transmission wires is:

Power lost = current * current * resistance.

Thus, doubling the voltage at which the power is transmitted, for a given power to be transmitted, that  reduces the current by a factor of 2, and the power lost is reduced by a factor of 4.

• ##### A lot of people don't understand (7+ / 0-)

these basic concepts & relationship between Power, Voltage and Current. These all refer to very different things, but in common speech, people often interchange them. I'm sure you can imagine that to an EE it's like fingernails on a chalkboard.

Sometimes it helps to use an analogy:
Here's one...

Freedom isn't free. So quit whining and pay your taxes.

[ Parent ]

• ##### Yup, DKos is awesome that way. Gawd, I love smart(3+ / 0-)
Recommended by:
side pocket, deha, kyril

people. :-)

Information is abundant, wisdom is scarce. The Druid

[ Parent ]

• ##### I think the source of the confusion is (5+ / 0-)

that "voltage" in the familiar V=IR is a different quantity than "voltage" in "high voltage power lines."  V=IR would apply to the voltage lost over the length of the cable, with appropriate caveats as the equation really applies to direct current.  "High voltage" would be the amplitude of the alternating voltage in the transmission line, akin to the "120 V" of household supply.

Sorry, just had to chip in to work some of the cobwebs out of that section of my brain.  Your post was informative and, as far as I can tell, correct.

that art thou

[ Parent ]

• ##### Huh?(2+ / 0-)
Recommended by:
KenBee, Ohiodem1

You said what I wrote was "not true", then came to the same conclusion:

if the voltage on the transmission lines can be higher, the current needed in those same transmission lines to deliver the original amount of power to the homes is smaller.
That's exactly what I was saying... just using a simple equation. Actually all these equations are very powerful, and mostly universal.

Freedom isn't free. So quit whining and pay your taxes.

[ Parent ]

• ##### The portion...(1+ / 0-)
Recommended by:
kyril

I highlighted and immediately corrected is at the top of my comment. About ohm's law. It has nothing immediately to do to with your conclusion. Here it is again:

In your equation, if voltage went up, current would actually go down to make the equation stay in balance.
This is not true.

The man who moves a mountain begins by moving away small stones. -Confucius

[ Parent ]

• ##### sure it is...(1+ / 0-)
Recommended by:
Ohiodem1

example:

P=I*V

P=200
I=10
V=20
200 = 10 * 20

Now, increase the voltage, but keep power the same:

P=200
I=x
V=40

solve for I...

I=5

voltage went up... current went down.

Freedom isn't free. So quit whining and pay your taxes.

[ Parent ]

• ##### First, let me apologize. I have a relative in the (1+ / 0-)
Recommended by:
kyril

hospital. It's a bit stressful here. So my tone is quick, short, poor and not like me normally. Really. I am sorry. Normally I would elaborate at length and be very subtle about my feelings.

Second, your comment seems very strongly to be responding to Mindful Nature's comment. I mean it is a reply to that comment after all. So the expression 'your equation' seems to refer to the equation he cites, namely ohm's law. You even go on then to say that the equation he needs is a different equation, namely the power equation.

Do you see the confusion there? Again, sorry that I am a bit short and thus less subtle/polite (ergo, dickish) tonight. Things are nasty here and I am using dKos as an escape. I felt like more perspective and clarity would reduce confusion.

The man who moves a mountain begins by moving away small stones. -Confucius

[ Parent ]

• ##### Oh, I see..(0+ / 0-)

no problem... happens all the time, these threads are hard to keep straight. I hope your relative gets well soon. There are certainly  more important things in life than discussing power equations on the internet.

Freedom isn't free. So quit whining and pay your taxes.

[ Parent ]

• ##### I agree with this. nt(1+ / 0-)
Recommended by:
kyril

Republicans are like alligators. All mouth and no ears.

[ Parent ]

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