just call it 2 phase

| wrote: | |> Does anyone have a 500 kV AC line directly to their home? No. |> |> OTOH, 220VDC would bother me more than 480VAC.
| | Why? Switching could be more of a problem with no zero crossings.
That *IS* why 220 VDC would bother more to have it running through my home than having 480 VAC running through my home.
| I have a 2400VAC line running along the property boundary line. I | suppose it would be feasible to have a dc to dc converter on poles to | distribute at the 110VDC level, but I do not expect that in my lifetime. | I do not think that I would want it. You might just as well have | rectifiers and switching supplies in the individual devices. That is how | all of my personal computers do it.
I don't want that much DC coming into my home, especially with utility fault currents.
I would draw the line at 600 volts for AC, and 48 volts for DC.
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James Sweet wrote:

Sure DC transmission has its advantages- at high voltages for long distances or for underwater or underground cables or for asynchronous connections between systems. All point to point rather than grid systems where specific technical requirements are needed or the distance is long enough that the savings in transmission costs exceed the costs of the end equipment. For mid level and distribution, it has serious disadvantages(no current zeros).- AC offers great advantages in switching and flexibility of networks and the optimization of voltage levels for the task at hand with relatively cheap and efficient transformers.
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On Wed, 25 Mar 2009 21:44:03 -0400 Michael A. Terrell
| If homes were still fed with DC, the generators would have to be a | couple miles from your home. Also, it doesn't have to pulse to charge a | battery.
If using Edison's 220/110VDC split system, even a couple miles would be way too far. Today would could do transmission, distribution, service, and utilization, and different DC voltages and keep it DC all the way. It would still not be as cheap as AC, but it is possible to do.
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snipped-for-privacy@ipal.net wrote:

Yawn. You could post something that makes sense, but you rarely do. Lots of stupid things can be done, but why, other than to prove someone's ignorance?
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On Fri, 27 Mar 2009 15:34:59 -0400 Michael A. Terrell
| | snipped-for-privacy@ipal.net wrote: |> |> On Wed, 25 Mar 2009 21:44:03 -0400 Michael A. Terrell
|> |> | If homes were still fed with DC, the generators would have to be a |> | couple miles from your home. Also, it doesn't have to pulse to charge a |> | battery. |> |> If using Edison's 220/110VDC split system, even a couple miles would be way |> too far. Today would could do transmission, distribution, service, and |> utilization, and different DC voltages and keep it DC all the way. It would |> still not be as cheap as AC, but it is possible to do. | | | Yawn. You could post something that makes sense, but you rarely do. | Lots of stupid things can be done, but why, other than to prove | someone's ignorance?
So you don't really understand electricity, eh?
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snipped-for-privacy@ipal.net wrote:

Projecting your failings again, or just another pathetic attempt at trolling?
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On Sun, 29 Mar 2009 03:57:55 -0400 Michael A. Terrell
| | snipped-for-privacy@ipal.net wrote: |> |> On Fri, 27 Mar 2009 15:34:59 -0400 Michael A. Terrell
|> |
|> |> |> |> On Wed, 25 Mar 2009 21:44:03 -0400 Michael A. Terrell
|> |> |> |> | If homes were still fed with DC, the generators would have to be a |> |> | couple miles from your home. Also, it doesn't have to pulse to charge a |> |> | battery. |> |> |> |> If using Edison's 220/110VDC split system, even a couple miles would be way |> |> too far. Today would could do transmission, distribution, service, and |> |> utilization, and different DC voltages and keep it DC all the way. It would |> |> still not be as cheap as AC, but it is possible to do. |> | |> | |> | Yawn. You could post something that makes sense, but you rarely do. |> | Lots of stupid things can be done, but why, other than to prove |> | someone's ignorance? |> |> So you don't really understand electricity, eh? | | | Projecting your failings again, or just another pathetic attempt at | trolling?
Actually, it is your inability to understand what you read that is a problem. In school, there was a subject called "reading comprehension". I guess you flunked that subject.
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snipped-for-privacy@ipal.net wrote:

More substandard trolling?
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Michael A. Terrell wrote:

You know, you could just filter him like I did, having done that, I don't see his posts, but I still see the useless crap you post in response to every one of them.
I'm starting to see why usenet is dying in favor of moderated discussion groups, I just wish the latter were more centralized and had a clean standardized interface.
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snipped-for-privacy@ipal.net wrote:

You could do these things but, in practice, it would be a rather stupid step backwards (and somehow involving changes from AC to DC, back to AC etc, ad nauseum. Inefficient and bloody expensive.
For distribution, service, utilization, and different DC voltages, there is no comparison, AC wins hands down. With regard to switching, again AC wins. For transmission- it is a balance between line and terminal costs (point to point systems, not grids) or an asynchronous connection is needed- then HVDC has advantages. These factors have been known for roughly 80 years or so. As for generation. DC is severely limited- so what do we do- generate AC (simpler, cheaper and more efficient) step it up or down with simple transformers and then use it in loads that generally don't care whether it is AC or DC or can be handled by an induction motor in a more efficient and far less complex machine than a DC machine.
So where to use DC? In those places where it provides a cost or technical advantage or a specific need for DC (long distance HV transmission, long cable systems, asynchronous links between grids, aluminum pot lines, electronic power supplies, etc.) However, for voltage level changing, switching, and most utilization, AC wins. That is a lesson that was learned over 100 years ago and modern electronics hasn't changed the situation. Wishful thinking to the contrary.
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| snipped-for-privacy@ipal.net wrote: |> On Wed, 25 Mar 2009 21:44:03 -0400 Michael A. Terrell
|> |> | If homes were still fed with DC, the generators would have to be a |> | couple miles from your home. Also, it doesn't have to pulse to charge a |> | battery. |> |> If using Edison's 220/110VDC split system, even a couple miles would be way |> too far. Today would could do transmission, distribution, service, and |> utilization, and different DC voltages and keep it DC all the way. It would |> still not be as cheap as AC, but it is possible to do. |> |> | You could do these things but, in practice, it would be a rather stupid | step backwards (and somehow involving changes from AC to DC, back to AC | etc, ad nauseum. Inefficient and bloody expensive. | | For distribution, service, utilization, and different DC voltages, there | is no comparison, AC wins hands down. With regard to switching, again AC | wins. For transmission- it is a balance between line and terminal costs | (point to point systems, not grids) or an asynchronous connection is | needed- then HVDC has advantages. These factors have been known for | roughly 80 years or so. As for generation. DC is severely limited- so | what do we do- generate AC (simpler, cheaper and more efficient) step it | up or down with simple transformers and then use it in loads that | generally don't care whether it is AC or DC or can be handled by an | induction motor in a more efficient and far less complex machine than a | DC machine. | | So where to use DC? In those places where it provides a cost or | technical advantage or a specific need for DC (long distance HV | transmission, long cable systems, asynchronous links between grids, | aluminum pot lines, electronic power supplies, etc.) | However, for voltage level changing, switching, and most utilization, | AC wins. That is a lesson that was learned over 100 years ago and | modern electronics hasn't changed the situation. Wishful thinking to | the contrary.
DC went from "you can't do that with DC" to "OK, now you can do that, but why would you, since it costs so much" for a lot of things.
I just can't figure what motivated Edison with DC so much other than trying to recoup what he had already invested, and not wanting to admit that he was wrong. That, or he though electric lights would be the only use for any form of electricity. Motors were around in plenty in those days, so he should have seen some alternative uses. I guess he had a comfy box to think in.
Edison's only hope of more distant power generation (essential when trying to exploit renewables like hydro) was some kind of transmission that could drive motor-generator sets at local areas. Maybe MVDC (8800/4400V) to drive big motors that turn his LVDC (220/110) generators? That would still be quite a nightmare to manage (motor genset maintenance vs. transformer maintenance).
Even I tried to dseign some kind of DC transformer. The best I came up with still involved rotating parts (think of a Faraday Homopolar generator with an equivalent motor piggybacked). Still a maintenance nightmare compared to what AC gets to use.
OTOH, extremely long electrical transmission is, IMHO, not a good idea, for two reasons. It wastes energy (where applicable ... you are stuck if the power mover source is a hydro dam, for example, or to get power from wind farms where the wind blows the most) in warming the transmission lines. And it is an exposure to terrorism. But where we must transmit power, HVDC can come out ahead despite its costs when considering not only the losses and risks in long distance transmission, but also managing reactive power flow. I'm guessing some costs for HVDC will come down, and I hope we do see more of HVDC transmission ... for where there is no choice but to do that. But I also want to see more localized generation where that is possible. It is still a balance. For example, transporting coal from PA/WV/KY to burn in localized power plants in the east and northeast would not make sense if that transporting is too costly or too exposed to terrorist attack (e.g. taking out a major rail bridge may deplete a power plant's 30 day supply, whereas a transmission line over the same river could be put back in just a few days).
BUT ... I still want to call that 240/120 VAC electricity coming into my home as TWO phases ... and connect more and more loads to BOTH phases.
AND ... I want to push for a cabinet full of computer boards/blades powered by a big single power supply (one per cabinet) that feeds 12 VDC to each of the boards, which is fed by 480 VAC (2 or 3 phases).
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wrote:

I don't think that MVDC motors even exist. AFAIK the largest universal motor in existence, is the traction motor of an E-Lok, supplied with 700 volts at the highest notch (1500 HP, 1 MW) The HV induction motors are quite common, they come in 3.3,6.6, 15 and 20 kV versions, ranging from 1 MW to ...whatever. One of the largest is the motor for the bucket wheel of a brown coal miner, which is supplied directly with 20 kV.

I don't think that can even be handled by the commutator and the brushes. Of course, the transformator having no moving parts, is a no-brainer....

Transporting the coal can't beat the efficiency of a well-designed trasmission line, which usually is around 99 %.

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wrote:
| I don't think that MVDC motors even exist. AFAIK the largest universal motor | in existence, is the traction motor of an E-Lok, supplied with 700 volts at | the highest notch (1500 HP, 1 MW) | The HV induction motors are quite common, they come in 3.3,6.6, 15 and 20 kV | versions, ranging from 1 MW to ...whatever. One of the largest is the motor | for the bucket wheel of a brown coal miner, which is supplied directly with | 20 kV.
We haven't needed them, yet.
| Transporting the coal can't beat the efficiency of a well-designed | trasmission line, which usually is around 99 %.
So then it makes more sense to place the power plant near the coal fields.
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snipped-for-privacy@ipal.net wrote:

------------ Look up the Thury system

It worked but not really well and died a natural death (oh, those damned AC transformers). The mecury arc rectifier was the breakthrough needed (about 40 years later in Sweden ), followed by the use of high power solid state equipment (initially at Eel River, New Brunswick, Canada).
As Dimitrious said, MVDC motors weren't available and, generally are not available now. High voltage, high current moving contacts (commutator) leads to problems that are best avoided. Note that for AC machines, the HV side is the stator- very helpful. Sure, 300V,1KA commutator generators do exist as exciters for AC machines but I doubt whether any of these are built nowadays -as brushless excitation (Fixed field, AC 3 phase rotor winding- feeding DC field through a bridge mounted on the rotor) is now being used to completely eliminate moving contacts.
With regard to long distance transmission - sure it would be nice for all to be local -and since real estate costs would exceed the savings involved and not all suitable sources are near the load centers- we are stuck with it. The reason for extremely long distance transmission is simply that many very desirable sources are also quite distant from load centers. There is a relationship between MW-miles and optimal voltage levels. In the case of hydro, Quebec's James Bay is a considerable distance from NYC and the hydro generation in BC and Washington is also quite far away from major load centers. As for coal generation- it has always made sense for generation to be near the coal source if at all possible- that hasn't changed. I think you are overestimating transmission losses as well as terrorist activities- Most terrorists aren't stupid enough to target transmission lines unless they want minimum bang for their buck.
By the way, DC transmission doesn't help manage reactive- these systems require reactive sources at both ends. What they do is eliminate "line reactive" needs and compensation in the form of shunt inductors and series capacitors.
As for your big 12VDC power supply -fine- possibly some gain in efficiency (questionable) there is the problem of a high power DC noting that each "tap" would have to have breakers capable of handling the full fault MW if interruption to all the computers is to be avoided. What you might gain from a single base supply is more than made up for by the cost /size of appropriate DC breakers.
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wrote:

Furthermore, nowadays electricity is generated in centralized locations (be it coal, hydro or nuclear-nuclear needs generally a large river nearby) or oil (mazut) or natural gas, as in the case of Crete. The most common for base loads is a steam plant, which runs for 1 1/2 years non stop after it has been synchronized. Here, in Crete we have large 2-stroke diesels (mazut fired) which run for 6 months, and small stem turbines (for 1 year). The grid HV here is 150 kV. In Kozani, where the brown coal veins are, it is raised from 21 kV to 400 kV for transmission to Athens and Thessaloniki, the main demand centres. I don't know whether terrorists would target the transmission lines, but breaker yards are heavily guarded, and extremely hazardous if you don't know what you're doing (even 150 kV would immediately vaporize a human upon direct contact). In Crete, furthermore, there are redundant transmission lines, for safety.
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I do remember visiting the Sylmar Pacific Intertie facility. They had some pretty large harmonic filter components out there. I don't remember if they were there to absorb harmonics generated from the switching or whether they compensated for reactive currents as well. I also do not remember how many pulses they used to approximate a sine wave from the switching banks.
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Salmon Egg wrote:

Basically harmonic compensation and the scheme would be roughly equivalent to a 6 phase supply (12 pulse- often with a star primary and delta and star secondaries feeding converters in series).Reactive would be drawn from the systems at each end and would depend on the control scheme used and the real power loading. Note that filtering will generally be on both the AC and DC sides.
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The power system that I worked in has machines with traditional excitation systems (DC generator, commutator, & slip rings) ranging from 250V, 800A to 375V, 3653A on the exciter nameplates.
Rectified AC exciters both brushless with rotating diode wheels and stationary rectifiers with slip rings were used on machines built after about 1965 and carried ratings like 525V, 8381A and 550V, 6009A. The high current one is brushless and the other one has slip rings. Something similar is probably used today on new machines.
The largest traditional DC machine I worked with was 375V, 3653A. It had all of the windings know to dc, including a pole face winding extension of the interpoles which I'd never seen on any smaller machine. I know that there were some larger DC machines used in steel mills at that time which have been superseded by variable frequency and adjustable speed AC drives. (VFD uses synchronous motors while ASD uses induction motors.)
In the late 80's, I worked on variable frequency ID fan drives that were rated 4500HP @ 945 RPM, 63Hz. They used synchronous motors and were probably similar to what would have been used in steel mills about the same time (late 1980's). The motor voltage was 2300V and they had 2 windings. Each winding was driven via a 3 phase frequency converter from an 11kV system. The converters were arranged to form a 6 pulse system for both the motor and power system so that the 5th and 7th harmonics cancelled. I sold them to the mechanicals as 'electron turbines'. ;-)
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Fred Lotte wrote:

As I recall, the pole face windings in series with the interpoles were used to counter the distortion of the field flux by the armature mmf. The armature mmf tends to weaken flux on one side of the field pole and increase it on the other side but some saturation can occur resulting in a weakening of the total flux. It happens in all machines but generally it isn't all that important in most cases. In the size of machine that you mention, it could be of concern. This machine would have been near the upper limit for conventional DC machines.
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I have not worked on this kind of machine. Tell me if I understand the principles correctly.
The armature reaction does distort the field as you describe. That shifts the neutral axis. That in turn means that the brushes now short out commutator segments that have more voltage between them than would be the case without armature reaction.
To get around these problems, the brushes can be rotated so to minimize the voltage between the segments that do get shorted. To avoid rotating the brushes, interpoles can induce an emf in the coils connected to adjacent commutator segments to reduce the voltage between segments that are shorted through the brushes. This avoids the necessity of rotating the brush assembly.
Do I have that right?
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