Effficiency of our power distribution structure

[soccerballtux]

?

 

[pm]

Good question.

How about:

http://en.wikipedia.org/wiki/E...ric_power_transmission

Transmission and distribution losses in the USA were estimated at 7.2% in 1995

 

[Eeezee]

Very inefficient. AC over long distances is pretty bad

High voltage DC is much more efficient, but we'll never build a new grid because we're lazy.

 

[soccerballtux]

Originally posted by: Eeezee
Very inefficient. AC over long distances is pretty bad

High voltage DC is much more efficient, but we'll never build a new grid because we're lazy.

WHAT? Electromigration much?

 

[BrownTown]

VERY efficient (in terms of human achievements), greater than 90% of the electricity generated at a power plant will reach the end user. Something like 93% is average despite traveling hundreds of miles. This whole story that the electric grid is a hulking pile of crap is full of it. the only problem is the fact that it is nearly impossible to get new transmission lines built due to NIMBY and environmental concerns. It can take a decade of litigation to get a line built even though EVERYONE knows its required. The electrical power generation systems is one of greatest (if not the single greatest) inventions of mankind.

As for HVDC, its less efficient for the vast majority of applications, only on the longest lines such as connecting the East and West coast, or connection abundant hydro or wind generation in low population state to high demand in a nother state hundreds of miles away. The break even point is on the order of 200+ miles for HVDC transmission. And a line of that length wil cost billions to build, so they don't come along every day.

EDIT: as for electromigration on HVDC, i've never heard of that outside of the metals layers on computer chips, would it really apply to power lines which are centimeters thick?

 

[F1shF4t]

Problem with HVDC is that you have to convert it to to AC and back or have DC to DC converter which are less efficient and a lot more costly than transformers.
A place where it would make some sence to use DC would be for SWER if you could get the dc to ac converters cheap enough. Line charging at low loads and huge voltage drops at higher loads are a b*tch on these 100+ km lines. Especially considering they use steel or other tiny copper or aluminium conductor.

Most short urban lines have typically less than 3% losses. Longer rural lines can approach more than 5% but generally when you get higher than that number you start hitting voltage constraints anyways.

BTW: HVDC advantage over long distances due to:
1. Resistance of conductor is less to DC than AC (no skin effect)
2. No need to worry about power factor (Cap banks, reactors, complex SVCs)
3. Easier to connect separate grids

Major dissadvantage is cost.

 

[soccerballtux]

Originally posted by: BrownTown
VERY efficient (in terms of human achievements), greater than 90% of the electricity generated at a power plant will reach the end user. Something like 93% is average despite traveling hundreds of miles. This whole story that the electric grid is a hulking pile of crap is full of it. the only problem is the fact that it is nearly impossible to get new transmission lines built due to NIMBY and environmental concerns. It can take a decade of litigation to get a line built even though EVERYONE knows its required. The electrical power generation systems is one of greatest (if not the single greatest) inventions of mankind.

As for HVDC, its less efficient for the vast majority of applications, only on the longest lines such as connecting the East and West coast, or connection abundant hydro or wind generation in low population state to high demand in a nother state hundreds of miles away. The break even point is on the order of 200+ miles for HVDC transmission. And a line of that length wil cost billions to build, so they don't come along every day.

EDIT: as for electromigration on HVDC, i've never heard of that outside of the metals layers on computer chips, would it really apply to power lines which are centimeters thick?

It applies to anything with current running through it. It's usually not a problem with most stuff (not enough current flow, for a long enough time; also there's much less of it with AC power (because electrons are just moving back and forth-- it's when you get to DC and you're pumping actual electrons from one side of the wire to the other that you get problems)). I recall an image of a bar of aluminum that had been conducting electricity in some big circuit or something for a while with visible pits near the left side and extra bumps on the right side-- the electrons had bumped the atoms out of place and eventually shifted them to the right. TBH, I don't know how long it was conducting though so it could be that the wires would only need to be recast every 50 years or something.

Can you provide any linkage so I can read about the power grid efficiency?
**actually, I just re-skimmed the wiki article; you're right on the money-- 92.8.

 

[soccerballtux]

Originally posted by: Dark Cupcake
Problem with HVDC is that you have to convert it to to AC and back or have DC to DC converter which are less efficient and a lot more costly than transformers.
A place where it would make some sence to use DC would be for SWER if you could get the dc to ac converters cheap enough. Line charging at low loads and huge voltage drops at higher loads are a b*tch on these 100+ km lines. Especially considering they use steel or other tiny copper or aluminium conductor.

Most short urban lines have typically less than 3% losses. Longer rural lines can approach more than 5% but generally when you get higher than that number you start hitting voltage constraints anyways.

BTW: HVDC advantage over long distances due to:
1. Resistance of conductor is less to DC than AC (no skin effect)
2. No need to worry about power factor (Cap banks, reactors, complex SVCs)
3. Easier to connect separate grids

Major dissadvantage is cost.

Thanks! Very informative.

 

[BrownTown]

I still don't think electromigration can be much problem for HVDC, there are tons of HVDC lines and I never hear of it being a problem. At whats the worst that could happen, you have to replace a piece of copper every 30 years? Thats not much cost compared to a several billion dollar transmission line. I'd be far more worried about the affects of single pole HVDC systems on buried metal objects.

 

[KIAman]

Although 93% transmission efficiency sounds great, when factored into real life usage, it's still a tremendous amount of power lost. According to EIA, total transmission loss is estimated at 266.277 billion kilowatt-hours for the year 2006 (they don't have any more recent data than that) for the USA.

Let's say the average kilowatt-hour costs 8 cents so that amounts to a loss of $21,302,160,000 in losses for that year.

Or, that is around 266 million tons of carbon released into the air.

 

[Modelworks]

The real problem isn't efficiency , its in the layout of the grid itself. It really needs a lot done to the infrastructure as the grid really hasn't improved much in 20 years. The power demands have gone up but the grid is still the same. It's like everything else in the USA , bridges, roads, etc . we are really behind on keeping these things up. The engineers gave the USA a D- on the state of things like that. The new bill in congress gives some money to things like this, but it's not anywhere near what is needed. Estimates are in the trillions of dollars to fix what is broken .

 

[soccerballtux]

Originally posted by: Modelworks
The real problem isn't efficiency , its in the layout of the grid itself. It really needs a lot done to the infrastructure as the grid really hasn't improved much in 20 years. The power demands have gone up but the grid is still the same. It's like everything else in the USA , bridges, roads, etc . we are really behind on keeping these things up. The engineers gave the USA a D- on the state of things like that. The new bill in congress gives some money to things like this, but it's not anywhere near what is needed. Estimates are in the trillions of dollars to fix what is broken .

I spoke with a prof and he confirmed this-- the efficiency won't get any better, it's the legislation that went through when we deregulated it all. The senators thought it was like piping gas; they didn't take into account that electricity follows the path of least resistance. Hence you can have a transformer blowing in North Dakota when the lines through Oklahoma are at 20% capacity.

The argument is that we can't wait the 5+ years it would take for a bill to get through (lots of billing technicalities politicians don't understand but would argue till dawn over). Right now the line holders are very wary to spend on fixing things, let alone improving/investing in a better line infrastructure, because the way the system currently works, it's near impossible for them to get any money (even revenue is difficult). If you've got Virginia and say Texas supply power through the same line to California, who gets what money? How much should the line owners get? The power plants take most of it and leave the line owners with little to nothing. They would love to fix the problem themselves (they could pay for it) were it not for the poorly-written deregulation bill.

Apparently this needs to be done (fixed) right away; we can't wait. It has very little to do with the efficiency (93% is pretty darn good), and seems to have everything to do with politics and billing problems.