AC vs DC Industrial Power Generation 1

[SCSWestport]

Can anyone point me in the direction of any authoritative articles on the relative efficiency of current industrial AC vs DC power generation?

Thanks

 

[waross]

Not much DC power generation left. automobiles have generated AC and rectified it to DC for decades now. Many younger mechanics may never have seen an automotive DC generator.
Dc motors were at one time controlled by motor generator sets generating DC but most are now driven and controlled by controllers that input and rectify AC. Even DC motors are being phased out in favour of VFD controlled AC motors. DC was once commercially available in large cities with trolly systems. It was used in major buildings for driving DC elevator motors. Most of these DC services were phased out around 50 years ago.
There is virtually no DC generation left. The number of applications where DC has been replaced by AC should give you a good overview of the relative overall efficiency and usability of AC versus DC.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricpete]

I agree.

You didn't ask about transmission systems, but I'll mention that dc has a number of advantages for transmission systems. Here are some things that spring to mind:
1 - It can be used to transfer power between separate ac grids which are not synchronized to each other
2 - Does not have the same stability-related limitations as ac related to transmitting real power through inductive paths.
3 - less or no skin effect means conductors can be smaller or cheaper or lighter. Also perhaps the transmitted current is slightly less because there are no vars (sudes?) to transport around
4 - Managing real power flow is simpler.
5 - Through control of power on dc systems, a certain small degree of improved indirect control is achieved for the ac systems that they connect to.

Note dc used to be at a big disadvantage due to higher cost of power electronics compared to transformers. The cost of electronics tends to decrease over time but cost of transformers does not.

Can anyone point me in the direction of any authoritative articles...

Disclaimer: I am not an authoritative refernce (I think you figured that out). If you have interest in benefits of dc on transmission side you might ask on the power forum.

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(2B)+(2B)' ?

 

[jraef]

DC generation is very different from DC transmission. DC generators are not in favor any more mostly because of the fact that for INDUSTRIAL applications, there is more wear and tear involved and then there is the fact that most END USE machinery is AC. So not only do you have to contend with brush / commutator wear and maintenance, you ALSO end up needed some other method of converting the DC to AC. It's much easier to just begin with AC.

But that said, it will also depend on the INDUSTRY you are talking about. If the preponderance of end use machinery or process uses DC, then it might make sense.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[electricpete]

DC generation is very different from DC transmission. [.quote]
Hence my first line: "You didn't ask about transmission systems, but..."


=====================================
(2B)+(2B)' ?

 

[SCSWestport]

I believe that Microgrids will change the paradigm.

Anyone have any thoughts on that?

 

[waross]

What is a microgrid?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gerbii]

Microgrid.. you mean decentralized power generation and consumption ? Doubt that, in general, DC machinery is more expensive than AC.
Adding to what have benn said before.. AC can be polyphase. AC machinery can grow much bigger than DC. This makes concentrated power generation cheaper.

"If an experiment works, something has gone wrong"

 

[TheBlacksmith]

Also, since DC has no zero crossings, interrupting under load or short circuit conditions can be interesting, so another nod in favor of AC.

 

[waross]

When I was starting out I saw and worked on a lot of DC. As the years go by I see less and less DC. Application after application switches from DC to AC. Even the newer diesel electric locomotives are going to AC drives. There are still nitches where DC is used but less and less. High voltage DC transmission is an exception, but the same thing that makes HVDC cost effective is making AC more cost effective in more and more applications.
The development of high voltage/high power semiconductor devices is making the difference.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DanEE]

"The development of high voltage/high power semiconductor devices is making the difference."

in particular the Insulated Gate Bipolar Transistor... Today's hybrid drive vehicles, super high efficiency UPS systems, mag-lev trains would not be possible without it..

http://www.ece.ncsu.edu/people/bjbaliga

http://people.engr.ncsu.edu/bjbaliga/IGBT_Applications_and_Social_Impact.pdf

 

[DRWeig]

Bill,

I didn't know you had been in the business long enough to remember the transition from Edison to Westinghouse.

I can only add to this discussion that in my 30 years of wandering around industrial plants, I've only run into one DC system, which was at a giant chromium smelting plant.



Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[rasevskii]

Missing from this discussion is the fact that DC is still the de-facto standard for urban electric traction systems. Trams, streetcars, subways, light rail, and trolleybuses all use DC at 600 or 750V. Some systems use 1500V or 3000V, local railways in Japan, Switzerland, and elsewhere often use the 1500V system. The Italian National railways use 3000V DC.

Third rail systems generally use 600 or 750V, however the BART system in The Bay Area of California uses third rail at 1000V. The Hamburg S-Bahn uses 1200V side-contact third rail.

All modern systems are supplied from Silicon rectifier substations. Gone are the mercury arc, synchronous converters, and MG sets of former decades. But some are still around, here and there.

rasevskii

 

[iop995]

Initial post was about efficiency AC vs DC power generation. Power generation without transmission it's an experimental or island system, so must clarify what is in discution. Country grid level system involve now AC after some small DC systems at the begining times, so I think it's not possible to change in DC (from economicaly PoV) thus efficiency of AC vs DC power generation it's a nonsense (I have excluded large DC power generation and conversion to AC transission system - a theorticaly possible solution but not practically). For island systems may be a good discussion about efficiency in power generation but technicaly or commercial conditions/requirments may be much important than possible small efficiency difference between AC / DC generation solution. For PV area systems, DC transmission may be a good option, but it's also a small line(s) at country / regional transmission system scale.