Washing machine 240, 50Hz - 240, 60 Hz?

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| | |> There are many aspects of the US/North American system I don't like. |> The 60 Hz is about the only thing I do like about it. I'd rather go
|> on up to 72 Hz. |> | | hmmm... 4320 RPM and 2160 RPM generators. More power in the same size | generator, but the turbines would change, some for the better, some for the | worse. | | X sub L of the power lines increased by 20%. Charging currents increase by | 20%.
Oh, well, then let's go to 36 Hz.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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This has been the subject of many discussions before. Go too low (and this includes 50 Hz AFIC) and the incandescent lamps will flicker because the filaments cool too quickly. Yes, I know it is just a matter of time before all incandescents will be CF lamps and LEDs, but we are not anywhere near that point yet.
Go too high and the inductive reactance of all power lines and transfomers increase (as noted by the previous poster). At 60 Hz, there are many large commercial/industrial two-pole high power generators that operate at 3600 rpm (driven by steam turbines at many nuclear plants, for example). At 72 hz, this would be 4320 rpm and include all the additional stresses that want to make a large flywheel type machine fly apart.
As for increasing the charging current, major cities like New York can't even keep the lights on in Queens during the summer because they have more charging current than they know what to do with. They even have to run over-excited generators with no load to generate negative VARS at times, just to keep the lights on.
Historically, 25 Hz works great for elevators and electric transit. 16 2/3 Hz works for many electric railroads.
Though, you can argue the point that the US 120V. utilization voltage is too low (and I would argue that it still contributes to a safer installation for residences even with GFI's and RCDs).,, I would argue that standardizing the frequency at 60 Hz instead of 50 Hz was something the US and Canada got right around 90-100 years ago.
If you don't like 50 Hz, you can blame Germany as they were Europe's manufactuer of most of the electrical equipment at the beginning of the 20th century.
Beachcomber
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| This has been the subject of many discussions before. Go too low (and | this includes 50 Hz AFIC) and the incandescent lamps will flicker | because the filaments cool too quickly. Yes, I know it is just a | matter of time before all incandescents will be CF lamps and LEDs, but | we are not anywhere near that point yet.
"all incandescents will be CF lamps and LEDs" ... ???
That would be a good trick. Be sure to patent it.
| Go too high and the inductive reactance of all power lines and | transfomers increase (as noted by the previous poster). At 60 Hz, | there are many large commercial/industrial two-pole high power | generators that operate at 3600 rpm (driven by steam turbines at many | nuclear plants, for example). At 72 hz, this would be 4320 rpm and | include all the additional stresses that want to make a large flywheel | type machine fly apart.
Note that I am not proposing this as where to change to. It is just what I think would have been a more ideal choice to begin with. All the things we have today that depend on either 50 Hz or 60 Hz would not have been created.
| Historically, 25 Hz works great for elevators and electric transit. | 16 2/3 Hz works for many electric railroads.
I bet that was the case for older designs. The elevators I have seen had a nice gearing system to step the rotary speed from the main drive motor down to the cable drum speed.
| Though, you can argue the point that the US 120V. utilization voltage | is too low (and I would argue that it still contributes to a safer | installation for residences even with GFI's and RCDs).,, I would | argue that standardizing the frequency at 60 Hz instead of 50 Hz was | something the US and Canada got right around 90-100 years ago.
120 volts is safer than 240 volts 60 volts is safer than 120 volts 30 volts is safer than 60 volts The NEC even lets you have exposed conductors at 30 volts.
But at some point the higher fault current also raises the danger.
Compare the danger of 120 volts 60 years ago to 240 volts today. I think that comes out about even. And that's for 240 volts L-N as they have in UK, Australia, Brazil, etc. I propose it would be better to have a L-L system as I believe most electrical shocks and electrocutions are L-G. The US system of 240 volts is really 120 volts L-G (as you know). My suggested system would be 288 volts L-G. Sure, it would have been more dangerous back 100 some years ago when it would have had to be deployed to make it economical to have today. And that risk may well have doomed any such proposal. Sadly, we have a less efficient system today because of historical risks that are way less significant today.
We have technology like GFCI that reduces the risks today. I wish we could have had that decades earlier.
Today we have much higher fault currents due to the demand for more power and the resultant larger transformer capacities. That isn't so much of a concern on long branch circuits with smaller wire. But it's a big concern in some places like inside panels.
I would not at all be bothered by 480 or 600 volts coming into my home on the service entrance and being stepped down by a transformer.
| If you don't like 50 Hz, you can blame Germany as they were Europe's | manufactuer of most of the electrical equipment at the beginning of | the 20th century.
Specifically blame Siemens.
Actually, the one thing I dislike about our electric services the most is the fact that most of it is L-N. I'd much rather have most things be L-L with the ground point about half way between. There ya go, a lower shock hazard right there. The exact voltage and frequency are not as much of the issue to me as the L-N vs. L-L configuration.
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On this point, I agree with you. A L-L system at 240 V. (120 max to ground) would give all the benefits (higher utilization voltage, lower current, lower insulation requirments (120 to ground) along with an earthed groundED conductor and avoidance of a neutral (whenever possible) and would promote maximum safety. When more safety is needed, a fault sensing GFCI or RCD could be used (on local invidual circuits, and/or as part of the the mains.
The only downside from a LL system, as far as I can determine, is that the mechanical complexity of breaking the circuit (by double ganging the contactors) is increased. The strictly L-N systems seems more suitable for use with a single-gang fuse
Earlier you stated that dryers should be required to have 240V. motors. Also a good point. I would say that this should apply to the larger sizes of window air conditioners as well. Perhaps a 30 amp 240 V. circuit with two hots and one safety ground (no neutral).
I'm not sure what you would do about ranges. The ranges in the USA require a current carrying neutral (for the lower settings, the clock, and the light) although it must be possible to design a range that operates on straight 240 volts as they are apparently the standard in Europe.
How about refrigerators? Are there any advantages to an all 240V refrigerator?
Beachcomber
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| The only downside from a LL system, as far as I can determine, is that | the mechanical complexity of breaking the circuit (by double ganging | the contactors) is increased. The strictly L-N systems seems more | suitable for use with a single-gang fuse
back in the days of fuses, this was certainly one consideration. The extra switch complexity would have been, too.
It's incandescent lights that mostly need the L-N voltage. But given that the ratio between L-N and L-L varies depending on the chosen phasing system, the design I described chose to use a separate system for lighting. Since incandescent actually benefits from a lower voltage, that's what I aimed for. With everything L-L on one system and everything L-N on another system, there is consistency in voltage between different phasing systems.
The system I chose was 20% higher in voltage and 20% higher in frequency. But it could just as well have been 240 volts L-L at 60 Hz (derived from 120 volts on single phase sources and 138.5 volts on three phase).
| Earlier you stated that dryers should be required to have 240V. | motors. Also a good point. I would say that this should apply to | the larger sizes of window air conditioners as well. Perhaps a 30 | amp 240 V. circuit with two hots and one safety ground (no neutral).
Then you could use a NEMA 6-30. Smaller things like a window air conditioner might only need NEMA 6-15.
| I'm not sure what you would do about ranges. The ranges in the USA | require a current carrying neutral (for the lower settings, the clock, | and the light) although it must be possible to design a range that | operates on straight 240 volts as they are apparently the standard in | Europe.
Just use the design from Europe, but with a small transformer for the light. And operate incandescent lights on 12 volts while at it.
| How about refrigerators? Are there any advantages to an all 240V | refrigerator?
Just like anything else. The current is smaller. The disadvantage is some switching needs to be double pole. But not all of it needs to be, such as the thermostat.
I noted that several computer power supply specs show more efficient operation at 240 volts.
Also, the US 240 volt system is already balanced power, so you get all the benefits of low ground hum that otherwise requires a 60-0-60 system to do that for 120 volt equipment (with the associated risks).
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AFAIK, all nuke's have 4 pole units. Lower steam pressure & no superheat (ok, B&W units have a little) result in a high steam flow for the size of the plant. The longer blades of a 1,800 RPM unit on the low pressure side are of greater benefit. Even with the lower speed, the 'big' units have 3 double flow low pressure units.
3600 RPM is the realm of gas turbines and coal / nat. gas fired steam units.
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why 36? or 72?
Actually the choice of 50/60 Hz is a compromise balance between a number of factors including economics. 25Hz was great for slow motors- particularly in the days when one motor was belted to a shaft and various lathes, etc were driven by belt connections to the same shaft. To hell with reading- people should be working. 16 2/3 Hz was/is used in some railway systems. 100Hz was also tried but L and C problems exist. 400Hz is fine for aircraft- smaller and lighter machines which could be driven by high speed turbines as used in aircraft while transmission distances were lower. As to 50 vs 60 Hz -historical (hysterical?) choices - probably including some politics. If you could encourage East Boondock to buy 60 Hz equipment- then they would go to the US for more -rather than to Europe. The Brits had a big Empire so there are more 50Hz systems than 60Hz (Canada is an exception). Clock gearing ratios are simpler at 60Hz (if you can still find a clock with a synchronous motor).
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| |> | |> |> There are many aspects of the US/North American system I don't like. |> |> The 60 Hz is about the only thing I do like about it. I'd rather go |> |> on up to 72 Hz. |> |> |> | |> | hmmm... 4320 RPM and 2160 RPM generators. More power in the same size |> | generator, but the turbines would change, some for the better, some for |> the |> | worse. |> | |> | X sub L of the power lines increased by 20%. Charging currents increase |> by |> | 20%. |> |> Oh, well, then let's go to 36 Hz. | | why 36? or 72? | | Actually the choice of 50/60 Hz is a compromise balance between a number of | factors including economics. | 25Hz was great for slow motors- particularly in the days when one motor was | belted to a shaft and various lathes, etc were driven by belt connections to | the same shaft. To hell with reading- people should be working. 16 2/3 Hz | was/is used in some railway systems. 100Hz was also tried but L and C | problems exist. 400Hz is fine for aircraft- smaller and lighter machines | which could be driven by high speed turbines as used in aircraft while | transmission distances were lower. | As to 50 vs 60 Hz -historical (hysterical?) choices - probably including | some politics. If you could encourage East Boondock to buy 60 Hz equipment- | then they would go to the US for more -rather than to Europe. The Brits had | a big Empire so there are more 50Hz systems than 60Hz (Canada is an | exception). Clock gearing ratios are simpler at 60Hz (if you can still find | a clock with a synchronous motor).
I suspect clocks were one basis for choosing 60 Hz. They already have a set of gears for reducing seconds to minutes at 60:1. At 60 Hz they need only one more.
Canada appears to be more influenced by the US than the UK.
I chose 72 Hz more for personal reasons than for technical reason, though. One reason is just to be different. If at a time when 50 and 60 had emerged, proposing a new standard would need to be different to avoid giving one group a specific advantage over another.
Another is that 72 Hz would have allowed using the same transformer core as is now used for 240 volts, but on 288 volts. I chose 288 volts mostly because it had some interesting numbers associated with it. Half the voltage is 144. Divide it by the square root of 3 and you get 166. Or multiply it by the square root of 3 and you get 499. In all cases, the numbers have the last 2 digits a "double", making these somewhat easier for people to say. Obviously not really a good technical reason.
The whole scheme would still work at 60 Hz and 240 volts on the L-L circuits and 24 volts on the L-N circuits. You'd just have either 120 volts to ground or 138.5 volts to ground, depending on whether you get the 240 from single phase or three phase. The idea is to use L-L more and have the same voltage between single phase and three phase.
I'd rather have seen TV run at 72 Hz. As you know, early TV frame rates were based on power frequency rates. We don't need to do that today, and haven't needed to for decades. Today some TVs do overscan anyway, and they tend to look a long better. 72 Hz is exactly 3 times the 24 fps traditional to film. But 60 Hz means some frames are 2 times and some are 3 times. It looks better when the multiplication is consistent.
Do you know why Japan has split 50 Hz and 60 Hz? At least that means there are some products made by manufacturers that have a motive to make sure they work on either 50 Hz or 60 Hz. I'll guess that they use the lower 100 volts to make the 50 Hz work on transformers that were really intended to operate on 120 volts at 60 Hz.
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Canada and the US are heavily interconnected. There is not much in the way of exclusive separation of the US-Canada electrical border.

As engineers, I would say that this is a fairly convoluted way of making a an intelligent selection. I think this sentiment is found more in the European countries than anywhere in North America. (To give a group a specific advantage might hurt the feelings of the others...even if the original group has the better system... Wow!?)
It reminds me of my mother's philosophy. "Each child must be treated fairly. If one has less, then it is my duty to give him more than the other one".
It also reminds me of communism.
Something so important with so much impact on future generations should be wisely chosen on having the best technical considerations with regard to economy, safety, ease of implementation, and a whole lot of other factors.
Edison thought DC was better. Westinghouse, Tesla, and when he was off on his own, Edison's own secretary Samuel Insull, saw the economy of an AC distribution system. The 1893 Chicago Columbian exhibition spread the wisdom and gospel of AC. The world proved it was economical, even though high voltage DC transmission were eventually perfected in the electronic age.
Beachcomber
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| |>I suspect clocks were one basis for choosing 60 Hz. They already have a |>set of gears for reducing seconds to minutes at 60:1. At 60 Hz they need |>only one more. |> |>Canada appears to be more influenced by the US than the UK. | | Canada and the US are heavily interconnected. There is not much in | the way of exclusive separation of the US-Canada electrical border. |> |>I chose 72 Hz more for personal reasons than for technical reason, though. |>One reason is just to be different. If at a time when 50 and 60 had emerged, |>proposing a new standard would need to be different to avoid giving one group |>a specific advantage over another. |> | As engineers, I would say that this is a fairly convoluted way of | making a an intelligent selection. I think this sentiment is found | more in the European countries than anywhere in North America. (To | give a group a specific advantage might hurt the feelings of the | others...even if the original group has the better system... Wow!?)
It's not about hurting feelings. There are real economic issues that are involved with decisions like that. It's easier to make decisions like that if you can go back in time before anyone has committed to it.
| It reminds me of my mother's philosophy. "Each child must be treated | fairly. If one has less, then it is my duty to give him more than the | other one". | | It also reminds me of communism.
It does not remind me of communism at all. It reminds me of the separation of government and business. Communism would have no businesses at all with the government running everything. But we do get an advantage of government establishing standards where there is economic disadvantage to having incompatibilities.
| Something so important with so much impact on future generations | should be wisely chosen on having the best technical considerations | with regard to economy, safety, ease of implementation, and a whole | lot of other factors.
I agree. I also believe that has never been done with any electrical system design.
| Edison thought DC was better. Westinghouse, Tesla, and when he was | off on his own, Edison's own secretary Samuel Insull, saw the economy | of an AC distribution system. The 1893 Chicago Columbian exhibition | spread the wisdom and gospel of AC. The world proved it was | economical, even though high voltage DC transmission were eventually | perfected in the electronic age.
I read that Tesla wanted 80 Hz or more.
DC transmission is practical now. But could we also do this for the distribution layer now? Would DC to the service drop be practical? If so, then we could freely choose whatever AC frequency we want, or just use the DC as it is.
Of course DC comes with it's own interesting issues. It's less practical for simpler motors, but probably just fine for controlled motors. It has no zero crossover, so fuses and circuit breaker fault issues are more significant.
DC GFCI breakers exist, but I bet they are more complex.
I'm not opposed to having DC all the way to the home. But just how safe and reliable are the means to step the voltage down? Is there any failure mode that makes it more likely to unleash distribution voltages to the home circuits than we would have with pole pig and pad mount transformers?
What voltage should we drop to homes in DC? 240?
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I think it comes down to a basic knowledge of physics. DC is coming into play again because people are installing solar and wind power systems.
High voltage is required for long distance transmission, but the world has not, and in my opinion, is not going to return to widespread dc transmission and distribution. Electrical engineers would mostly agree that 1000 volts per mile makes sense for AC transmission.
With DC, at present, there is no safe and economical way of converting say 115, 000 kv at thousands of locations to a safe utiliazation voltage at many many multiple locations. The installations that do support terminations for dc transmission lines are large, largely custom designed, and very expensive.
Personally, I don't think the era of a DC central station in every town is going to come back. Do you have information to the contrary?
Beachcomber

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| |> |>I'm not opposed to having DC all the way to the home. But just how safe |>and reliable are the means to step the voltage down? Is there any failure |>mode that makes it more likely to unleash distribution voltages to the |>home circuits than we would have with pole pig and pad mount transformers? |> |>What voltage should we drop to homes in DC? 240? |> | | I think it comes down to a basic knowledge of physics. DC is coming | into play again because people are installing solar and wind power | systems.
And maybe I need to consider that direction given the not so great level of inverters I'm finding on the market.
| High voltage is required for long distance transmission, but the world | has not, and in my opinion, is not going to return to widespread dc | transmission and distribution. Electrical engineers would mostly | agree that 1000 volts per mile makes sense for AC transmission. | | With DC, at present, there is no safe and economical way of converting | say 115, 000 kv at thousands of locations to a safe utiliazation | voltage at many many multiple locations. The installations that do | support terminations for dc transmission lines are large, largely | custom designed, and very expensive.
So basically, it can be done for special cases, but it's not practical for the common cases (at least not yet).
| Personally, I don't think the era of a DC central station in every | town is going to come back. Do you have information to the contrary?
I have no such info. What I am wondering about is, if it would be possible or practical to distribute power that stays DC all the way from where it is generated to to the home/office. I guess the answers would be "perhaps and no".
I guess we are stuck with AC from the utility in my lifetime but might need to consider DC utilization for off-grid home power systems.
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I know of lots of people, especially in the more remote and desert regions of the US that generate their own power. I am assuming you have checked out homepower magazine, which has been available on the web for years.
http://www.homepower.com /
Though I live in a suburb and will probably be tied to the grid for at least the next few year, I've enjoyed reading about the success stories that people have had with the German "Sunny-Boy Inverters" and others. Apparently, you can get into important but exotic subjects like what is the impedance of your utilities power transformer from the point of your service entrance.

Ok, I wasn't sure of your knowledge level. My background is an EE who works more with computers, but I've always had an interest in power systems.
Yes, there are DC Transmission Systems all over the world, some of them work quite long distances and some are in undersea cables. Wikipedia well tell you all about it.
The US even has a few. The one where I live (in Oregon) feeds power back and forth (at different times) from the Oregon side to the Columbia River to and from Los Angeles.
The convertor stations are big, expensive, and contain equipment that is exotic when compared to the typical AC transmissions stations. The used to use mercury arc rectifiers, but now I believe they are all solid state.
Back in Edison's day, there were no sockets, dynamoes, wire, insulation, fuses, switches or meters readily available for sale. They had to practically build everything from scratch.
Yet, they were successful and the first DC Central Station came on line in the crowded Pearl District area of New York City in 1882. The voltage was 110 volts and the maximum distance for customer service was about one mile.
Beyond that, you have the classic problem with DC. Even at this distance the mains had to use extremely large diameter wire... else the lights would dim out to zero output. One mile was about the maximum economical distance for a complete low voltage dc system and that is derived from the laws of physics.
Soon, many towns had "Central Station" service. If you can ever get a copy of one of the early trade magazines, "Electrical World", I believe it is called. It offeres a fascinating glimpse of this era.
This leads to the story of the "Battle of the Currents", AC vs. DC. Tesla, Westinghouse, and the development of the electric chair which I'm not going to attempt to re-tell here, but you can certainly read about it from other sources.
Bottom line, high voltage DC was (and still is) pretty much only good for long-distance transmission for limited point-to-point service. In the pre-electronic age, there was no economical and efficient way to convert DC high transmission voltages to a safe distribution voltage for every customer that needed it in the sprawling wide areas. . New York City offered DC for elevator power distribution to certain districts until fairly recently, I'm told, but, like a central station, most of the customers were clustered in one relatively small area.
What revolutionized AC was the invention of the transformer by Lucien Gaulard and John Gibbs in the early 1880's. Like the radio triode inventor Lee DeForest, these guys didn't really understand their invention very well and kept hooking them up incorrectly (in series) until other engineers stepped in to fix the technical problems. Like the birth of the electric chair, this itself is a fascinating story...

Do you live within a mile of the power plant? Then the answer is maybe yes? Would they be willing to install DC generators just for you?
Or. is your office a few miles from a coal mine or hydro plant? Then you could have point-to-point dc transmission at a higher voltage, but they might make you pay for all of the extra equipment needed.
Beachcomber
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| |>| |>| I think it comes down to a basic knowledge of physics. DC is coming |>| into play again because people are installing solar and wind power |>| systems. |> |>And maybe I need to consider that direction given the not so great level |>of inverters I'm finding on the market. |> | I know of lots of people, especially in the more remote and desert | regions of the US that generate their own power. I am assuming you | have checked out homepower magazine, which has been available on the | web for years. | | http://www.homepower.com /
Yes. But I am doubtful of what they cover. All the systems people are talking about in these cases are rather small. Considering the lack of fault current issue I'm finding in inverters, it looks like I might need a rather hefty system, even if I am going to cut back on the power actually used.
One target load is a full size electric cooktop with dual oven. I want to rule out using gas on this (at least for now) because gas is a fossil fuel and it need needs a tie-in to an infrastructure (pipes or trucks) in most cases. Being able to do all my cooking on energy gathered renewably on the property is a goal. Generating hydrogen to do that is a possible other option to explore (and I would need to explore the viability and safety of using hydrogen as a cooking fuel).
| Though I live in a suburb and will probably be tied to the grid for at | least the next few year, I've enjoyed reading about the success | stories that people have had with the German "Sunny-Boy Inverters" and | others. Apparently, you can get into important but exotic subjects | like what is the impedance of your utilities power transformer from | the point of your service entrance.
If you want to sell power back to the grid, those might be a good choice. But even those models come relatively small.
My original thought was to have inverters of a size needed to run the cooking, and just duplicate that for other circuits, maybe 3 or 4 total power segments. But with the low fault current issue, now it looks like it might be better to gang them all together and target a very high end level of current, at least enough to trip any branch circuit breaker. The other extreme is to distribute DC and put inverters at point-of-use without concern for the faults.
But in any case, an inverter must be able to survive a bolted fault, even if it just shuts itself down.
|>So basically, it can be done for special cases, but it's not practical |>for the common cases (at least not yet). |> | Ok, I wasn't sure of your knowledge level. My background is an EE who | works more with computers, but I've always had an interest in power | systems.
My background is CS but I took some EE classes, none of which were power systems. My interest in power has developed over the past few years based on sime issues that I've had with powering data centers. I found that if I learned the electrical codes, I could specify circuits for large numbers of computers without electricians coming back and saying something won't comply with codes. It has expanded from there.
| Back in Edison's day, there were no sockets, dynamoes, wire, | insulation, fuses, switches or meters readily available for sale. | They had to practically build everything from scratch.
There wasn't a lack of knowledge. Electricity had been around for 80 years by then, and electrical power had been commercially produced for many years before Edison got involved in it, some AC, some DC. What Edison did was make a big market for it. You couldn't just pick up some some insulated wire at the corner store, but it was available from more than one manufacturer. The science of the insulation was, though, still quite young.
| Yet, they were successful and the first DC Central Station came on | line in the crowded Pearl District area of New York City in 1882. The | voltage was 110 volts and the maximum distance for customer service | was about one mile. | | Beyond that, you have the classic problem with DC. Even at this | distance the mains had to use extremely large diameter wire... else | the lights would dim out to zero output. One mile was about the | maximum economical distance for a complete low voltage dc system and | that is derived from the laws of physics.
It was actually a 220 volt system, in terms of how far it could be run for a given amount of total power used.
| This leads to the story of the "Battle of the Currents", AC vs. DC. | Tesla, Westinghouse, and the development of the electric chair which | I'm not going to attempt to re-tell here, but you can certainly read | about it from other sources.
Read that several years ago.
| What revolutionized AC was the invention of the transformer by Lucien | Gaulard and John Gibbs in the early 1880's. Like the radio triode | inventor Lee DeForest, these guys didn't really understand their | invention very well and kept hooking them up incorrectly (in series) | until other engineers stepped in to fix the technical problems. Like | the birth of the electric chair, this itself is a fascinating story...
They effectively invented the current transformer :-)
Series, whether transformer connected or not, was a fundamental problem. It did solve certain problems that make it useful in certain situations even today. For example lights inaccessible to ordinary people can be powered in series at an overall rather high voltage to maintain each at the same current level. Parallel wiring leads to distant lights at a lower voltage, so you can't just tweak the voltage to get them at the level you want.
If you want to keep a string of lights at equal voltage over very long runs, you might consider the method posted about half-way down in this thread:
http://www.electrical-contractor.net/ubb/Forum1/HTML/007078.html
|>I have no such info. What I am wondering about is, if it would be possible |>or practical to distribute power that stays DC all the way from where it |>is generated to to the home/office. I guess the answers would be "perhaps |>and no". |> | Do you live within a mile of the power plant? Then the answer is | maybe yes? Would they be willing to install DC generators just for | you?
I think that's a "low voltage" issue rather than a DC issue. If there is a _practical_ and _safe_ way to step DC up to high voltage and then step it back down, then "DC over one mile" is not an issue.
This is about low voltage ... and about DC not really being practical for common voltage changing (yet). DC itself is not inherintly the cause of this limitation; the fact that it can't be economically transformed is. Solve that tranformation issue and DC works.
| Or. is your office a few miles from a coal mine or hydro plant? Then | you could have point-to-point dc transmission at a higher voltage, but | they might make you pay for all of the extra equipment needed.
AC is still the practical means to transmit and distribute power. That may change some day in the future.
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Buffalo NY has these, or at least had them in the early '80s. What is a transformer with a "mechanically floating secondary windings", and why is such useful for that type of circuit? How does bypassing a blown bulb work, did they parallel each bulb with a device similar to a Zener diode that conducts if the voltage exceeds a certain level, keeping the voltage drop across it constant?
Of some interest, what they seem to use to power the lights was a setup on a pole with a large transformer can, a small can and something else about the size of the small can. I don't know what each component was.
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     snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) writes:

Reading, Berks, UK had such a system. There were a number of series circuits, all driven from the basement of the old town hall, at least up to the 1970's.

The circuits are constant current, and the series streetlamp bulbs came in a few different power ratings intended for constant current operation. (I don't recall what current was used, but I think it was in the region of 6A.)

It was paralleled with a device which shorts out when a high voltage appears across it, just like series fairy lights. With the supply being a constant current supply, the remaining lamps continue running at their rated power, but the total voltage supplied to the series chain drops. Each chain has a volt meter on it, and you can look at them and tell how many lights are out on each chain by how much the chain voltage is reduced. You could also do this my monitoring the counter-weight position on the floating transformer windings, although I never actually saw the transformers driving the system in Reading.
Also available was control gear for 400W mercury vapour lamps to run from the series chains, and this was actually what was in use by the time I saw the system in Reading, although it might have started off with filament lamps. There's a lamp failure bypass mechanism for these too, but I can't now remember how it worked.
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writes:

The secondary coil was free to move on the core and was counterbalanced. If the current was too high , the coil moved away from the primary and the coupling weakened a bit. If low, it moved closer to the primary. Whether there is a core gap, I cannot recall. In effect it was a kind of constant current device. As to the bulbs- it was much simpler than a zener diode. If a bulb blew, then the total line voltage appeared across it and across a small disc in parallel. This would break down and act as a short circuit across the bulb. A similar thing is built into Xmas light bulbs. Cheap, simple, one shot.
I don't know what was in the small cans. one was probably a photo sensor and the other may have a contactor used to close the main circuit.
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| As to the bulbs- it was much simpler than a zener diode. If a bulb blew, | then the total line voltage appeared across it and across a small disc in | parallel. This would break down and act as a short circuit across the bulb. | A similar thing is built into Xmas light bulbs. Cheap, simple, one shot.
All the Xmas lights I have seen are voltage sourced. That is, the whole series string is driven by a constant voltage. So if a burned out bulb results in a device shorting out with less resistance than the filament had, the whole current level will rise. At some point it will begin to cascade through all the bulbs. There would need to be a fixed resistance in each to prevent that from happening. And these are very cheap lights.
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wrote:

----------------- Sure they are cheap- there is a downside to that. There may be a fixed resistor or a fuse built into the plug- I don't know? Since these are cheap and other causes for string failure exist "which bulbs have loose or poor contacts or are kaput" you are faced with the choice: a)waste a lot of time trying to find the problem which usually arises after you have tested and then put them up to find a dead string when it is cold enough to make you a eunuch. b)buy a device which helps you do this (in theory-I have one-better than hunt and peck and cost more than a new string of the little incandescent bulbs) and possibly not waste as much time. c) simply throw the string into the trash and spend the time with a hot toddy.
Your preference- I know mine.
I have a LED string which has a couple of dead lamps -can't replace them but It appears that the design is robust enough to allow for this so that after continuous use for a few months, no further failures have occurred.
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