115V/400Hz
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barit1,
We were talking AC frequency, no?
In aircraft, where you transmit power only over a couple of hundred feet at the most, the losses in the wiring (skin effect, etc.) are far less significant than the gain in weight of transformers and other equipment.
When you have to transmit power to a train over what may be tens of kilometres (depending on the distance between substations), the equation flips the other way, and switching to a lower frequency than even the standard European 50Hz starts making sense. Which is was the Swiss did.
How's that again? Long distances? Swiss railways?
In aircraft, where you transmit power only over a couple of hundred feet at the most, the losses in the wiring (skin effect, etc.) are far less significant than the gain in weight of transformers and other equipment.
When you have to transmit power to a train over what may be tens of kilometres (depending on the distance between substations), the equation flips the other way, and switching to a lower frequency than even the standard European 50Hz starts making sense. Which is was the Swiss did.
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No technical quarrel, ChristiaanJ. I'm just not calibrated to think in terms of long distances in Switzerland.
Texas maybe, or certainly Oz, or...
(A terrifying thought: How did they know 16 2/3 hz wouldn't interfere with the alphorns?
)
Texas maybe, or certainly Oz, or...
(A terrifying thought: How did they know 16 2/3 hz wouldn't interfere with the alphorns?
)
Train buffs department.
The Swiss (and German and Austrian) electric railways use 16 2/3 Hz supply because they were initially designed in 1910-1920, and were in fact the first major AC railways, previous ones being DC apart from some experiments. They only continue with this system because of what they already have in place.
The low frequency was chosen primarily because they were using comparatively large and heavy mechanical elements for which 1,000 rpm was OK but 3,000 rpm was not. Nothing to do with the transmission but to do with the various revolving parts in the substation and on the locomotive.
Since that time any new electric AC railway system has invariably used 50 Hz. The arrival of semiconductors in the 1950s to take the place of the rotating machines sealed the point.
The railway in the US from New York to Washington was electrified at 25 Hz in the early 1930s but in recent times they did do a conversion to 50 Hz (and had a lot of changeover work to do, it must have been worth it).
http://en.wikipedia.org/wiki/15_kV_AC
If you are concerned about long-distance transmission (or, on a railway, long distances between substations, which are expensive) you use as high a voltage as you can, hence the 25Kv standard. One or two new schemes have actually gone for 50 Kv.
The Swiss (and German and Austrian) electric railways use 16 2/3 Hz supply because they were initially designed in 1910-1920, and were in fact the first major AC railways, previous ones being DC apart from some experiments. They only continue with this system because of what they already have in place.
The low frequency was chosen primarily because they were using comparatively large and heavy mechanical elements for which 1,000 rpm was OK but 3,000 rpm was not. Nothing to do with the transmission but to do with the various revolving parts in the substation and on the locomotive.
Since that time any new electric AC railway system has invariably used 50 Hz. The arrival of semiconductors in the 1950s to take the place of the rotating machines sealed the point.
The railway in the US from New York to Washington was electrified at 25 Hz in the early 1930s but in recent times they did do a conversion to 50 Hz (and had a lot of changeover work to do, it must have been worth it).
http://en.wikipedia.org/wiki/15_kV_AC
If you are concerned about long-distance transmission (or, on a railway, long distances between substations, which are expensive) you use as high a voltage as you can, hence the 25Kv standard. One or two new schemes have actually gone for 50 Kv.
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More Trivia
1. Many people have survived being struck by lightening. Some of them several times. Very high VOLTAGES are not necessarily fatal.
2. Grazing cattle are often killed by nearby - not direct - lightening strikes because of the steep voltage gradient in the earth between their front and rear feet. Moral : if caught out in a storm keep your feet close together.
3. Electric chairs used for killing people in certain barbaric cultures use DC.
4. Long undersea cables used to interconnect electricity grids in different countries eg France and UK use DC.
2. Grazing cattle are often killed by nearby - not direct - lightening strikes because of the steep voltage gradient in the earth between their front and rear feet. Moral : if caught out in a storm keep your feet close together.
3. Electric chairs used for killing people in certain barbaric cultures use DC.
4. Long undersea cables used to interconnect electricity grids in different countries eg France and UK use DC.
Off the track a bit, but electric fencer to keep cattle, sheep, horses, etc. give 5-8000 volts. Caught it a few times and it makes you jump but no harm done.
This is because the current is very low.
Safe flying!
This is because the current is very low.
Safe flying!
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So why did BA change from empower to 115v/60Hz?
One of the more dubious changes I have seen is the new BA club world at-seat power supply which is now 115v at the floor rather than the 15v empower system.
Despite the fact that inevitably it will have trip protection, how can it be safer?
I used the system recently and I continually got 'belts' from touching the metal parts of the new seat. In the dark, upstairs on a 744, I rested my right hand on the metal of the table, and my left hand brushed the side of my laptop, one of these 'wee blue sparks" jumped from my hand to the unoccupied USB port on the machine, which promptly said "there has been a power surge and this point will be shut down as a precaution".
So I am not convinced its a positive development. Is this a grounding issue?
Despite the fact that inevitably it will have trip protection, how can it be safer?
I used the system recently and I continually got 'belts' from touching the metal parts of the new seat. In the dark, upstairs on a 744, I rested my right hand on the metal of the table, and my left hand brushed the side of my laptop, one of these 'wee blue sparks" jumped from my hand to the unoccupied USB port on the machine, which promptly said "there has been a power surge and this point will be shut down as a precaution".
So I am not convinced its a positive development. Is this a grounding issue?
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Going to 400Hz rather than say 50/60Hz does not save much copper weight but it saves the iron which makes up the magnetic components of transformers and motors.
In a typical 50Hz 3000VA transformer (that uses reasonable quality laminations) the core would weigh around 20kg.
At 400Hz this goes down to around 5kg; a big weight saving.
There is some copper weight saving because the turns per volt scale inversely with the cross sectional area of the core etc and a smaller transformer will need a shorter length of wire to make each turn around the core. But there is no wire diameter saving because the current is still the same.
Skin effect is negligible at 400Hz.
The other reason for 400Hz is that in the old days one did have solid state DC-AC inverters; one used a motor driving a generator to do such conversions. And the output frequency is the RPM divided by the # of poles of the rotor. The smallest number of poles physically possible is 2 and that means a 50Hz generator has to run at 3000rpm. This is inconveniently slow. A 400Hz generator can run at 24000rpm or, more usefully, can have more poles for the same rpm and thus be more compact.
Nowadays one would not bother with 400Hz because of solid state inverters using lightweight ferrite cores and operating at tens of kHz, but this is old history.
In a typical 50Hz 3000VA transformer (that uses reasonable quality laminations) the core would weigh around 20kg.
At 400Hz this goes down to around 5kg; a big weight saving.
There is some copper weight saving because the turns per volt scale inversely with the cross sectional area of the core etc and a smaller transformer will need a shorter length of wire to make each turn around the core. But there is no wire diameter saving because the current is still the same.
Skin effect is negligible at 400Hz.
The other reason for 400Hz is that in the old days one did have solid state DC-AC inverters; one used a motor driving a generator to do such conversions. And the output frequency is the RPM divided by the # of poles of the rotor. The smallest number of poles physically possible is 2 and that means a 50Hz generator has to run at 3000rpm. This is inconveniently slow. A 400Hz generator can run at 24000rpm or, more usefully, can have more poles for the same rpm and thus be more compact.
Nowadays one would not bother with 400Hz because of solid state inverters using lightweight ferrite cores and operating at tens of kHz, but this is old history.
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Some input on the voltage/frequency/current questions
Voltage
Usa does generally use 115v 60hz A.C. but has other voltages 220etc available in some areas. It is correct that the lower voltage is "safer" in similar conditions than say the european standard 230v. it is also down to the design of the transformers as in distrubution systems all voltages are referenced to earth. The neutral generally being connected to earth.
In many areas the earth connection is actually in the center of the transformer winding so halving the voltage to earth this in the UK is particularly on building sites where 230/110 volt transformers are used - so you get 50v from either output wire to earth but 110v between. Some U.S. systems use this.
The U.K. power system was designed for small numbers of large substations feeding an area so the higher voltage (240v) was used to reduce voltage drop problems on longer runs, though Blackpool for one originally was a 110v system. The U.S. system uses a mid level (possibly 1000v distrubution with smaller transformers feeding individual or small groups of properties.
Both work for them.
DC undersea cables i.e. France to U.K. is because France uses 60Hz frequency & U.K. 50 Hz - try connecting them together and it is BANG Big BANG. also losses in D.C are lower at Higher currents.
Swiss railways vwith 16 2/3 Hz was simply that before the invention of clever electronic kit A.C. motors were virtually impossible to speed control. It was found that by using that frequency D.C. controls & motors could be used thus saving the expense of costly A.C. to D.C. rotary convertors or latterly massive valve types.
3phase motors are much simpler as a single phase motor needs mulit sets of ciols and a capacitor to start it. the simplest 3 phase motors need 3 static coils and an aluminium (usually) cage that spins, the 3 pase sets up a rotating magnetic field, this is induced into the cage and it spins.
Sorry can'y help on the 400hz bit unless it is to do with connecting alternators in parrallel - but I don'y know if that is done on a/c
Sorry thats long & hope it helps
Usa does generally use 115v 60hz A.C. but has other voltages 220etc available in some areas. It is correct that the lower voltage is "safer" in similar conditions than say the european standard 230v. it is also down to the design of the transformers as in distrubution systems all voltages are referenced to earth. The neutral generally being connected to earth.
In many areas the earth connection is actually in the center of the transformer winding so halving the voltage to earth this in the UK is particularly on building sites where 230/110 volt transformers are used - so you get 50v from either output wire to earth but 110v between. Some U.S. systems use this.
The U.K. power system was designed for small numbers of large substations feeding an area so the higher voltage (240v) was used to reduce voltage drop problems on longer runs, though Blackpool for one originally was a 110v system. The U.S. system uses a mid level (possibly 1000v distrubution with smaller transformers feeding individual or small groups of properties.
Both work for them.
DC undersea cables i.e. France to U.K. is because France uses 60Hz frequency & U.K. 50 Hz - try connecting them together and it is BANG Big BANG. also losses in D.C are lower at Higher currents.
Swiss railways vwith 16 2/3 Hz was simply that before the invention of clever electronic kit A.C. motors were virtually impossible to speed control. It was found that by using that frequency D.C. controls & motors could be used thus saving the expense of costly A.C. to D.C. rotary convertors or latterly massive valve types.
3phase motors are much simpler as a single phase motor needs mulit sets of ciols and a capacitor to start it. the simplest 3 phase motors need 3 static coils and an aluminium (usually) cage that spins, the 3 pase sets up a rotating magnetic field, this is induced into the cage and it spins.
Sorry can'y help on the 400hz bit unless it is to do with connecting alternators in parrallel - but I don'y know if that is done on a/c
Sorry thats long & hope it helps
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Rainboe,
Good question, and I hope somebody well-informed can fill us in on the background.
My first reaction was "weight"....
"Hydraulic" is now a "mature" technology, and you'd need a breakthrough to significantly bring down the weight.
"Electric" is still evolving, with new materials, more efficient switching and control electronics, etc.
So possibly the "cross-over point" has been reached, where tossing out the entire hydraulic system and replacing everything, even the "big" stuff, with electrical systems, allows you to bring down the weight enough to make it worth the effort.
Happened years ago on choppers, when we started replacing hydraulic flying control actuators (autostab, autopilot) with electrical ones.
Good question, and I hope somebody well-informed can fill us in on the background.
My first reaction was "weight"....
"Hydraulic" is now a "mature" technology, and you'd need a breakthrough to significantly bring down the weight.
"Electric" is still evolving, with new materials, more efficient switching and control electronics, etc.
So possibly the "cross-over point" has been reached, where tossing out the entire hydraulic system and replacing everything, even the "big" stuff, with electrical systems, allows you to bring down the weight enough to make it worth the effort.
Happened years ago on choppers, when we started replacing hydraulic flying control actuators (autostab, autopilot) with electrical ones.
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Thanks west lakes,
At least the civil aircraft industry ended up standardising largely on 115V 400Hz and 28VDC, unlike the railways, where everybody went their own way.
1.5kV DC, 3kV DC, 750V DC third rail, 25kV 50Hz, 15kV 16 2/3 Hz.... take your pick. And there are certainly others.
Hence some TGVs runing on international routes, and the Thalys, and the Eurostar, which are all "tri-tension" (but not the same voltages, LOL)..
At least the civil aircraft industry ended up standardising largely on 115V 400Hz and 28VDC, unlike the railways, where everybody went their own way.
1.5kV DC, 3kV DC, 750V DC third rail, 25kV 50Hz, 15kV 16 2/3 Hz.... take your pick. And there are certainly others.
Hence some TGVs runing on international routes, and the Thalys, and the Eurostar, which are all "tri-tension" (but not the same voltages, LOL)..
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other bits
yea not forgetting the Frence CC 40100 loco with 4 voltage choices!
Forget to mention the current bits
50mA (.05) can kill an adult!! especially if current flow is through the heart.
Myth - the electricity threw me
Sorry your own automatic reflexes couples with your muscle contaction does the throwing usually around 30mA. Lots of reports in my industry of severe injuries to the guy stood behind as someones arm retracts from the shock!
Cattle fences are usually around 50v as a voltage that low can produce enough current to kill a cow. warning they are very painful if you step across one and end up with one leg either side & contact is made - think about it!
Forget to mention the current bits
50mA (.05) can kill an adult!! especially if current flow is through the heart.
Myth - the electricity threw me
Sorry your own automatic reflexes couples with your muscle contaction does the throwing usually around 30mA. Lots of reports in my industry of severe injuries to the guy stood behind as someones arm retracts from the shock!
Cattle fences are usually around 50v as a voltage that low can produce enough current to kill a cow. warning they are very painful if you step across one and end up with one leg either side & contact is made - think about it!
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50mA (.05) can kill an adult!! especially if current flow is through the heart.
There is almost no way to kill with electricity unless current passes through the heart. Anywhere else, you need a lot more current; enough to cause tissue damage through heating.
Cattle fences are about 10,000V - I have designed a few of the units
One uses a car ignition coil, usually. The current is very low. But they can kill a horse (via a heart attack, presumably) if it gets tangled up in the wire and I am aware of one case near here.
There is almost no way to kill with electricity unless current passes through the heart. Anywhere else, you need a lot more current; enough to cause tissue damage through heating.
Cattle fences are about 10,000V - I have designed a few of the units
One uses a car ignition coil, usually. The current is very low. But they can kill a horse (via a heart attack, presumably) if it gets tangled up in the wire and I am aware of one case near here.
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IO540 is right....and at voltages below 50V it becomes difficult to get enough current across a human body to kill, even with wet hands.
IIRC the standard for low-voltage power tools for hazardous environments is 48V, but I may be wrong.
115V is about the limit.... I've had the odd whack from 220V and 240V, but just been lucky.
Maybe a historian can tell us why America choose 100V (nominal, the 110V, then 115V, is just to account for the losses). Maybe that was OK for the insulation materials of the day, and by the time technology progressed, too many installations were in place to change?
Europe went for 200V (again 220V and 240V to account for the losses). Some low-voltage distribution systems went for 127V, which is the phase-to-neutral voltage for a three-phase network with 220V between phases.
As to cattle grids, yes, they're 5kV to 10kV but such a high internal resistance (that good old law of Ohm...) that they're not capable of delivering a mortal current, just a very nasty shock....
Sorry to hear about the horse.... I would have thought some sort of simple trip device in the supply could prevent that.
IIRC the standard for low-voltage power tools for hazardous environments is 48V, but I may be wrong.
115V is about the limit.... I've had the odd whack from 220V and 240V, but just been lucky.
Maybe a historian can tell us why America choose 100V (nominal, the 110V, then 115V, is just to account for the losses). Maybe that was OK for the insulation materials of the day, and by the time technology progressed, too many installations were in place to change?
Europe went for 200V (again 220V and 240V to account for the losses). Some low-voltage distribution systems went for 127V, which is the phase-to-neutral voltage for a three-phase network with 220V between phases.
As to cattle grids, yes, they're 5kV to 10kV but such a high internal resistance (that good old law of Ohm...) that they're not capable of delivering a mortal current, just a very nasty shock....
Sorry to hear about the horse.... I would have thought some sort of simple trip device in the supply could prevent that.
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Electrical accidents
The comments on the dangers of voltages refer.
There are numerous accounts in the electricty industry of linesmen surviving high voltage accidents (11kV, 33kV and even higher) as a result of the discharge arc tending to track on the surface of the skin rather than through the heart. The bad news is that these accidents result in horrendous burns with subsequent death or disfigurement.
It is interesting to see that although high voltage network switching is rigourously controlled with SOPs, permits, cross checking, control rooms with radio links, radio procedures and readbacks etc etc, accidents still occur as result of a combination of things like time pressure, severe weather, taking shortcuts, attention lapses etc - sound familiar???
There are numerous accounts in the electricty industry of linesmen surviving high voltage accidents (11kV, 33kV and even higher) as a result of the discharge arc tending to track on the surface of the skin rather than through the heart. The bad news is that these accidents result in horrendous burns with subsequent death or disfigurement.
It is interesting to see that although high voltage network switching is rigourously controlled with SOPs, permits, cross checking, control rooms with radio links, radio procedures and readbacks etc etc, accidents still occur as result of a combination of things like time pressure, severe weather, taking shortcuts, attention lapses etc - sound familiar???
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accidents
I'll stand corrected on the fence question.
ChristiaanJ
Not sure I agree and your take on relation of phase to neutral & phase to phase Uk system is ph - ph is 1.732 (root3) times ph to n. i.e before beurope standardised 415/240.
James Ozzie
Yes burns are the bigger risk, injured persons have had to have limbs removed to avoid death.
Though all this is off the original thread hope it shows the dangers of electricity.
But the good news is that like airline industry such major incidents are rare biggest cause of injury to UK staff is slipping, tripping and falling over - is that familiar also
ChristiaanJ
Not sure I agree and your take on relation of phase to neutral & phase to phase Uk system is ph - ph is 1.732 (root3) times ph to n. i.e before beurope standardised 415/240.
James Ozzie
Yes burns are the bigger risk, injured persons have had to have limbs removed to avoid death.
Though all this is off the original thread hope it shows the dangers of electricity.
But the good news is that like airline industry such major incidents are rare biggest cause of injury to UK staff is slipping, tripping and falling over - is that familiar also
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james ozzie,
Only a few days ago, a kid got killed here in France, climbing on top of a goods wagon - to recover a football IIRC. Drew an arc from the live 25kV overhead catenary .... Got quite a lot of TV coverage, to alert as many people as possible.
I like this thread, even if it deals with a lot of disjointed subjects....
The choice of 115V, of 400Hz, of single-phase and three-phase, of 28V DC, of DC for certain circuits and AC for others, are in a way all totally disconnected.
In a different world, we might well have seen 230V, 500Hz, and 48V DC as the aviation standard.....
And to add another spot of trivia....
Concorde electrical signalling (fly-by-wire if you prefer) used 1800Hz for the synchros, etc. to cut down as much as possible on interference from harmonics of the basic 400Hz systems.
Only a few days ago, a kid got killed here in France, climbing on top of a goods wagon - to recover a football IIRC. Drew an arc from the live 25kV overhead catenary .... Got quite a lot of TV coverage, to alert as many people as possible.
I like this thread, even if it deals with a lot of disjointed subjects....
The choice of 115V, of 400Hz, of single-phase and three-phase, of 28V DC, of DC for certain circuits and AC for others, are in a way all totally disconnected.
In a different world, we might well have seen 230V, 500Hz, and 48V DC as the aviation standard.....
And to add another spot of trivia....
Concorde electrical signalling (fly-by-wire if you prefer) used 1800Hz for the synchros, etc. to cut down as much as possible on interference from harmonics of the basic 400Hz systems.
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ChristiaanJ
The accident you describe is not uncommon over here, as well as the ill advised that try to walk?? along third rail DC lines in the south.
All absolutely tragic and unneccesary.
Saw a photo of two overhead transformers in Scotland this week, covered in gaffiti. The "artist" had been within 0.5m of live 11,000V (our safety approach is 1.2m
All this despite warning signs on all live equipment as per EEC
The accident you describe is not uncommon over here, as well as the ill advised that try to walk?? along third rail DC lines in the south.
All absolutely tragic and unneccesary.
Saw a photo of two overhead transformers in Scotland this week, covered in gaffiti. The "artist" had been within 0.5m of live 11,000V (our safety approach is 1.2m
All this despite warning signs on all live equipment as per EEC
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Originally Posted by west lakes
Not sure I agree and your take on relation of phase to neutral & phase to phase Uk system is ph - ph is 1.732 (root3) times ph to n. i.e before europe standardised 415/240.
UK is nominally "240V". "Europe" is nominally "220V", although most has now shifted to "230V".
So 127V/220V is right. And "Europe" is standardised "220/380". At least that's still the terminology, although it's now really "230/400". Only the UK is 240/415 nominal.
And another spot of trivia....
Nowadays a lot of equipment is capable of working over a very wide range of voltages. Thingies like hair curlers or traveling irons, or battery chargers, will often work between 100V and 240V without even having to set a switch.
But light bulbs.... we brought a batch of nominally 240V light bulbs back from the UK to France.... and boyo, they lasted far longer than the nominally 230V bulbs we bought here..... Yet the difference is less than 5%.
Last edited by ChristiaanJ; 18th May 2007 at 21:30.
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were all supposed to be 230/400, the main defference is the permitted variation. we had + or- 6% ion 240V its now +10 -6.
the lightbulb one is good one - you should see how short a life a 230v bulb has here! Actually saw on a US website advice to use europen bulbs there on 115V - apparently they last forever
the lightbulb one is good one - you should see how short a life a 230v bulb has here! Actually saw on a US website advice to use europen bulbs there on 115V - apparently they last forever