115V/400Hz
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The "artist" had been within 0.5m of live 11,000V (our safety approach is 1.2m
I used to design HV power supply units, and it's suprising how (not) far electricity will jump across a dry air barrier.
30kV DC will jump about 5mm; maybe 10mm if between sharp points. A 25kV AC wire would need to be practically touched before it will get you.
The highest I ever worked on was 500kV DC and that would jump about 1-2ft, between aluminium balls about 1ft diameter. The customer required it to withstand a number of short circuits - quite spectacular
1.2m at 11kV is hugely excessive but probably right if one is to assume the person might slip and fall over as well.
Back to the subject, 400Hz is also used to drive instrument movements that use the synchro principle; these would need to be much bigger if working at say 400Hz, and if working at much more, say 4000Hz, they would probably end up emitting noise. I believe 400Hz is also used for the fluxgate magnetometer. So there is so much stuff that has been designed around 400Hz over so many years, and I guess most of it is pretty proven and reliable, that nobody wants to change it. The electronics designers working on avionics are a long way from the sharpest - with annovation in avionics moving at snail's pace, most good people leave - and it pays to stick to tried and tested old principles.
I used to design HV power supply units, and it's suprising how (not) far electricity will jump across a dry air barrier.
30kV DC will jump about 5mm; maybe 10mm if between sharp points. A 25kV AC wire would need to be practically touched before it will get you.
The highest I ever worked on was 500kV DC and that would jump about 1-2ft, between aluminium balls about 1ft diameter. The customer required it to withstand a number of short circuits - quite spectacular
1.2m at 11kV is hugely excessive but probably right if one is to assume the person might slip and fall over as well.
Back to the subject, 400Hz is also used to drive instrument movements that use the synchro principle; these would need to be much bigger if working at say 400Hz, and if working at much more, say 4000Hz, they would probably end up emitting noise. I believe 400Hz is also used for the fluxgate magnetometer. So there is so much stuff that has been designed around 400Hz over so many years, and I guess most of it is pretty proven and reliable, that nobody wants to change it. The electronics designers working on avionics are a long way from the sharpest - with annovation in avionics moving at snail's pace, most good people leave - and it pays to stick to tried and tested old principles.
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Hmm
Just remembered london underground used to use high frequency a.c. (and possibly british rail) when flourescent lights were first introduced. this was to keep size of rotary dc to ac convertors down & also to reduce the flicker effect from the lights (as the sine wave hits zero volts) in an enclosed space. 50hz was/is thought to be connected to epileptic fits. this does not affect filament bulbs. wouldn't surprise me if the same thoughts were applied as a factor in a/c
Just remembered london underground used to use high frequency a.c. (and possibly british rail) when flourescent lights were first introduced. this was to keep size of rotary dc to ac convertors down & also to reduce the flicker effect from the lights (as the sine wave hits zero volts) in an enclosed space. 50hz was/is thought to be connected to epileptic fits. this does not affect filament bulbs. wouldn't surprise me if the same thoughts were applied as a factor in a/c
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west lakes,
Epileptic fits are associated with lower frequencies (several Hz, but not 50Hz). Fluorescent tubes flicker at 100Hz, BTW.
I would think if they indeed used higher frequency AC, it was for the same reasons as in aircraft : lower weight, smaller transformer cores, smaller inverters, smaller chokes for the TL tubes, etc.
Epileptic fits are associated with lower frequencies (several Hz, but not 50Hz). Fluorescent tubes flicker at 100Hz, BTW.
I would think if they indeed used higher frequency AC, it was for the same reasons as in aircraft : lower weight, smaller transformer cores, smaller inverters, smaller chokes for the TL tubes, etc.
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ChristiaanJ
agreed thats why i said was/is (some people don't belive those who know).
Have seen old electrical books that used to advise spreading flourescents over 3 phases to reduce this effect which would work out at 300hz.
at the end of the day some of the answers sought will have
been lost in the mists of time
Bon Soir (about the only french I can remember)
agreed thats why i said was/is (some people don't belive those who know).
Have seen old electrical books that used to advise spreading flourescents over 3 phases to reduce this effect which would work out at 300hz.
at the end of the day some of the answers sought will have
been lost in the mists of time
Bon Soir (about the only french I can remember)
Psychophysiological entity
1. Many people have survived being struck by lightening. Some of them several times. Very high VOLTAGES are not necessarily fatal.
I'm not sure if it was in the Guinness book of records or some other source, but I recall reading that 11 times was the maximum recorded . I'm also not sure if it was the 11th or 12th strike, that hit his tombstone!
I got hit by a spray of secondaries, on a boat dock while cranking the jet ski into the water. It bl00dy hurt.
what will kill you best
To all people arguing what kills and what doesn't (current vs. voltage):
If you're still young at heart (as I once was), you can go on a country ride and stop by a pasture with an electric fence. Grab a 2 ft long green (still moist, not dried out) grass blade by one end and rest the other end on the fence. You shouldn't feel anything. Slowly slide the grass blade towards the fence. At some point you should feel a somewhat unpleasant pulsed sensation. It will get stronger the closer you get to the fence wire. (If you are within 1 inch of the wire and still don't feel anything, the fence is OFF, or your grass is dead dry: abort.). If you did this experiment with a 10000V transmission line, you would likely be dead and learn a valuable lesson.
What protected you is the combination of your skin resistance, the (adjustable here) resistance of the grass blade, and the internal resistance of the fence generator. There is also pulsed, limited power nature of the generator, but let's not complicate things. The 10000V transmission line has pretty much no limits of its own. A capacitor charged to 10000V is also not likely to kill you because of the limited energy it can store and deliver.
Now, you can grab a 12V battery, one terminal with each hand and won't even notice. This battery could deliver over 100 Amps but here nothing happens.
You need a combination of sufficient voltage and low enough total path resistance to deliver the killing jolt. (Yes, it has to go through the heart. Time also matters.)
The resistance of your skin protects you up to about 40V. (It's just a rule of thumb, don't sue me.) Above that, please treat all wires as if they were spinning propellers.
So to conclude, yes, for academic purposes, it is the current through the heart of sufficient duration that kills. But when you face an exposed wire, for your safety you should mind its voltage. You will rarely know what limits are set in the generator circuits.
Poorly informed speculation:
Curiously, I used to think that you are probably more likely to be electrocuted by a household voltage of 110/220V than with a 10000V line because before your hand can get close enough to the 10000V line to convulse and latch on to it, it will arc through (high resistance) air gap of a few inches giving you a nasty warning.
BM
(edits in italics after learning from the wiser post below)
If you're still young at heart (as I once was), you can go on a country ride and stop by a pasture with an electric fence. Grab a 2 ft long green (still moist, not dried out) grass blade by one end and rest the other end on the fence. You shouldn't feel anything. Slowly slide the grass blade towards the fence. At some point you should feel a somewhat unpleasant pulsed sensation. It will get stronger the closer you get to the fence wire. (If you are within 1 inch of the wire and still don't feel anything, the fence is OFF, or your grass is dead dry: abort.). If you did this experiment with a 10000V transmission line, you would likely be dead and learn a valuable lesson.
What protected you is the combination of your skin resistance, the (adjustable here) resistance of the grass blade, and the internal resistance of the fence generator. There is also pulsed, limited power nature of the generator, but let's not complicate things. The 10000V transmission line has pretty much no limits of its own. A capacitor charged to 10000V is also not likely to kill you because of the limited energy it can store and deliver.
Now, you can grab a 12V battery, one terminal with each hand and won't even notice. This battery could deliver over 100 Amps but here nothing happens.
You need a combination of sufficient voltage and low enough total path resistance to deliver the killing jolt. (Yes, it has to go through the heart. Time also matters.)
The resistance of your skin protects you up to about 40V. (It's just a rule of thumb, don't sue me.) Above that, please treat all wires as if they were spinning propellers.
So to conclude, yes, for academic purposes, it is the current through the heart of sufficient duration that kills. But when you face an exposed wire, for your safety you should mind its voltage. You will rarely know what limits are set in the generator circuits.
Poorly informed speculation:
Curiously, I used to think that you are probably more likely to be electrocuted by a household voltage of 110/220V than with a 10000V line because before your hand can get close enough to the 10000V line to convulse and latch on to it, it will arc through (high resistance) air gap of a few inches giving you a nasty warning.
BM
(edits in italics after learning from the wiser post below)
Last edited by balsa model; 21st Jun 2007 at 22:52.
Do not try this at home...
Balsa,
I think you summarised it very well but your last comment perhaps needs clarification. If you were to draw an arc off a high voltage utility conductor to your body, you WOULD be history. I have an earlier posting on this subject which points out the not infrequent cases of power arcs tracking over the skin surface, resulting in appalling burns but not sending the heart into fibrillation. The poor victim instead dies a very nasty death from the burns and associated infections. Of course, people have survived the burns but I have no statistics.
I think you summarised it very well but your last comment perhaps needs clarification. If you were to draw an arc off a high voltage utility conductor to your body, you WOULD be history. I have an earlier posting on this subject which points out the not infrequent cases of power arcs tracking over the skin surface, resulting in appalling burns but not sending the heart into fibrillation. The poor victim instead dies a very nasty death from the burns and associated infections. Of course, people have survived the burns but I have no statistics.
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....before your hand can get close enough to the 10000V line....
Thanks for the warning. I wasn't going to test this theory.
I am not an expert by any means in this field, but reading survivor stories, it seems to me that in the case of "arcing electrocution" (where there is no direct contact with the conductor), something else is happenning, at least some of the time. Is it that it is the arcing plasma that causes all the burns? Does it have some momentum?
I would expect the skin to be penetrated in two spots only and our body fluids to form an attractive path of least resistance in between. (Sorry to be so non-chalantly graphic about it.) So why such extensive skin burns?
BM
(not morbid for its own sake, just curious)
I am not an expert by any means in this field, but reading survivor stories, it seems to me that in the case of "arcing electrocution" (where there is no direct contact with the conductor), something else is happenning, at least some of the time. Is it that it is the arcing plasma that causes all the burns? Does it have some momentum?
I would expect the skin to be penetrated in two spots only and our body fluids to form an attractive path of least resistance in between. (Sorry to be so non-chalantly graphic about it.) So why such extensive skin burns?
BM
(not morbid for its own sake, just curious)
Plasma
BM,
Yes, it is the plasma that burns (not the electricty). The plasma is the "4th state of matter" and is a very good conductor of electricity. The initial microscopic breakdown of air into ionised components allows a very rapid build up of heat therefore more ions therefore more conduction therefore more heat - hence a "power arc" develops in microseconds after the initial discharge (much faster than you can move your hand away...). A similar sequence applies with lightning strikes.
The very nature of this stuff is such that there is little analytical information available - it is all empirical/anecdotal. My guess that the reason power arcs track the skin surface is that the plasma is so hot and so well established that it is actually a lower resistance path than the wet body fluids. This would fit the instances of these observed surface burn injuries.
Yes, it is the plasma that burns (not the electricty). The plasma is the "4th state of matter" and is a very good conductor of electricity. The initial microscopic breakdown of air into ionised components allows a very rapid build up of heat therefore more ions therefore more conduction therefore more heat - hence a "power arc" develops in microseconds after the initial discharge (much faster than you can move your hand away...). A similar sequence applies with lightning strikes.
The very nature of this stuff is such that there is little analytical information available - it is all empirical/anecdotal. My guess that the reason power arcs track the skin surface is that the plasma is so hot and so well established that it is actually a lower resistance path than the wet body fluids. This would fit the instances of these observed surface burn injuries.
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Some additional bits and pieces.
IO540
Just checked clearances in the UK supply industry are: -
up to 33kV .8m, 132kV 0.7m added to these is an application factor dependant on the work involved e.g. when climbing a pole add .3m, working platform level on a pole add 2.1m. I'd added an extra .1 earlier - coward. these apply in all conditions and are err on the side of safety.
Plasma
Probably the major factor, try putting your bare hand near a welding arc see what happens (definately don't try this at home). As you say a lot of data is not analyitical. We are advised to wear cottton clothing (synthetics melt into the skin - seen this on advice for air travel as well) and are issued with Nomex Arc-Resistant clothing. This is tested, in Canada, to 25kV. we are told that if worn over no other clothing body protected from heat effects of arc.
As B.M. says depends on Ohms law voltage/resistance = current. Whist the 50mA figure I quoted earlier is accepted its only an average, similarly body resistence varys on the individual and on external e.g. weather conditions.
Deep burns seem to be one of the major causes of severe effects. I am sure we all have burnt the odd finger etc. over our lives these cause a blister and swelling. Current flow through the body causes the same under the skin E.G. to muscles etc. these cause limbs to swell and can only be relieved by surgically cutting the skin or ulimately amputation.
B.M.
actually not far wrong, far more killed by electrical shock in domestic incidents at lower voltages than work related at higher voltages. Also at lower voltages the arc & burning effects are less likely and less evident. At higher voltages the shear ammount of burns can hide the fact that the heart was affected by electrical shock, it could have been physical shock!
If one or both them spots are fingers or toes you can also expect to lose them, heating effect of current flow through a resistance. In most UK systems the live to earth current can be up to 1000A (we limit it)
Some anecdotes
Early 80's a worker came into contact with an 11kV line whilst erecting an aluminuim flag pole at an agricultural show (about 15 miles from where I'm sat) I wasn't involved with the investigation, too junior at the time, but he survived but lost a number of toes in the incident and sufferd burns to the palms of his hands.
6 months earlier a 14 yr old killed erecting a CB aerial contact with an 11kv line.
A worker wheeling a portable scaffold came into contact with a 132kv line, survived, current flow burnt off parts of limbs, deep burns led to amputation of lower arms and legs. Appeared on some safety fims telling his story. Sadly I have been told he eventually took his own life.
90's A mentally ill patient left a local hospital deliberately climbed a 132kV pylon, the barbed wire and climbing guard didn't bother him, leant out and lost his life with contact with live conductor. The steelwork apparently was a mess afterwards.
Christaan J
2 weeks later a "drunken" young person climbed an 11kv pole in southern england same result.
Don't forget also on high structures if the current doesn't kill you the fall might!
On that note and slightly lighter, in the 70's a person in the Bristol area decided to take his life by climbing a 400kV pylon, climbed the structure, climbed down the insulator string ans sat on the conductors - nothing happenned. Decided he had rubber soled shoes on so climbed back up the insulayors took them off and climbed back down - nothing happenned. was eventually rescued from the position.
It was a dry day the insultator strings are long enough not to be bridged when climbing down them.
On returning him to ground level a remark was made he would have been better jumping he hasd been at 100m agl
IO540
Just checked clearances in the UK supply industry are: -
up to 33kV .8m, 132kV 0.7m added to these is an application factor dependant on the work involved e.g. when climbing a pole add .3m, working platform level on a pole add 2.1m. I'd added an extra .1 earlier - coward. these apply in all conditions and are err on the side of safety.
Plasma
Probably the major factor, try putting your bare hand near a welding arc see what happens (definately don't try this at home). As you say a lot of data is not analyitical. We are advised to wear cottton clothing (synthetics melt into the skin - seen this on advice for air travel as well) and are issued with Nomex Arc-Resistant clothing. This is tested, in Canada, to 25kV. we are told that if worn over no other clothing body protected from heat effects of arc.
As B.M. says depends on Ohms law voltage/resistance = current. Whist the 50mA figure I quoted earlier is accepted its only an average, similarly body resistence varys on the individual and on external e.g. weather conditions.
Deep burns seem to be one of the major causes of severe effects. I am sure we all have burnt the odd finger etc. over our lives these cause a blister and swelling. Current flow through the body causes the same under the skin E.G. to muscles etc. these cause limbs to swell and can only be relieved by surgically cutting the skin or ulimately amputation.
Curiously, I used to think that you are probably more likely to be electrocuted by a household voltage of 110/220V
actually not far wrong, far more killed by electrical shock in domestic incidents at lower voltages than work related at higher voltages. Also at lower voltages the arc & burning effects are less likely and less evident. At higher voltages the shear ammount of burns can hide the fact that the heart was affected by electrical shock, it could have been physical shock!
I would expect the skin to be penetrated in two spots
Some anecdotes
Early 80's a worker came into contact with an 11kV line whilst erecting an aluminuim flag pole at an agricultural show (about 15 miles from where I'm sat) I wasn't involved with the investigation, too junior at the time, but he survived but lost a number of toes in the incident and sufferd burns to the palms of his hands.
6 months earlier a 14 yr old killed erecting a CB aerial contact with an 11kv line.
A worker wheeling a portable scaffold came into contact with a 132kv line, survived, current flow burnt off parts of limbs, deep burns led to amputation of lower arms and legs. Appeared on some safety fims telling his story. Sadly I have been told he eventually took his own life.
90's A mentally ill patient left a local hospital deliberately climbed a 132kV pylon, the barbed wire and climbing guard didn't bother him, leant out and lost his life with contact with live conductor. The steelwork apparently was a mess afterwards.
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.
2 weeks later a "drunken" young person climbed an 11kv pole in southern england same result.
Don't forget also on high structures if the current doesn't kill you the fall might!
On that note and slightly lighter, in the 70's a person in the Bristol area decided to take his life by climbing a 400kV pylon, climbed the structure, climbed down the insulator string ans sat on the conductors - nothing happenned. Decided he had rubber soled shoes on so climbed back up the insulayors took them off and climbed back down - nothing happenned. was eventually rescued from the position.
It was a dry day the insultator strings are long enough not to be bridged when climbing down them.
On returning him to ground level a remark was made he would have been better jumping he hasd been at 100m agl
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I have a problem in this subject.
Hi
It would be my pleasure if you help me in my problem.
I am working on an Alternating current motor for use in an actuator for using an a model. (115v 400Hz a tiny motor)
But my customer wants me to pass all test that a real airplane have.
I have a problem in High temp stall. In this test when the shaft of rotor is locked, we put the motor in a high temp chamber and energized it. The motor should be bear about 1 hour without any problem.
but after about 15 min when the temp raise to 140 C it is failed, May you please help me in this problem?
Best regard
Eng, Santi Chou
It would be my pleasure if you help me in my problem.
I am working on an Alternating current motor for use in an actuator for using an a model. (115v 400Hz a tiny motor)
But my customer wants me to pass all test that a real airplane have.
I have a problem in High temp stall. In this test when the shaft of rotor is locked, we put the motor in a high temp chamber and energized it. The motor should be bear about 1 hour without any problem.
but after about 15 min when the temp raise to 140 C it is failed, May you please help me in this problem?
Best regard
Eng, Santi Chou
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On why 400hz
The original reason was a tradeoff between weight ( higher frequency is better) and iron core losses due to hysteresis where lower is better. At the time initial systems were designed ~400 was the sweet spot.
Core material has evolved but too much installed base to make it worth changing.
The original reason was a tradeoff between weight ( higher frequency is better) and iron core losses due to hysteresis where lower is better. At the time initial systems were designed ~400 was the sweet spot.
Core material has evolved but too much installed base to make it worth changing.
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Why does my charger work?
1.
My wall charger (iPhone, Laptop) says it would accept 50-60Hz.
I have never found a problem with using them on any plane outlet though. Cockpit, Galley, Lavatory.
Why is it that way? Does it not matter if it's 50, 400 or 10000 Hz ?
2.
Are the shaving outlets in the Lav any different?
Because old shavers used to run a little faster in the USA (60Hz) than back home in Germany (50Hz).
My wall charger (iPhone, Laptop) says it would accept 50-60Hz.
I have never found a problem with using them on any plane outlet though. Cockpit, Galley, Lavatory.
Why is it that way? Does it not matter if it's 50, 400 or 10000 Hz ?
2.
Are the shaving outlets in the Lav any different?
Because old shavers used to run a little faster in the USA (60Hz) than back home in Germany (50Hz).
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The motor should be bear about 1 hour without any problem.
but after about 15 min when the temp raise to 140 C it is failed, May you please help me in this problem?
but after about 15 min when the temp raise to 140 C it is failed, May you please help me in this problem?
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1.
My wall charger (iPhone, Laptop) says it would accept 50-60Hz.
I have never found a problem with using them on any plane outlet though. Cockpit, Galley, Lavatory.
Why is it that way? Does it not matter if it's 50, 400 or 10000 Hz ?
2.
Are the shaving outlets in the Lav any different?
Because old shavers used to run a little faster in the USA (60Hz) than back home in Germany (50Hz).
My wall charger (iPhone, Laptop) says it would accept 50-60Hz.
I have never found a problem with using them on any plane outlet though. Cockpit, Galley, Lavatory.
Why is it that way? Does it not matter if it's 50, 400 or 10000 Hz ?
2.
Are the shaving outlets in the Lav any different?
Because old shavers used to run a little faster in the USA (60Hz) than back home in Germany (50Hz).
As to shavers, good question. I believe old shaver did not use a motor as such, just a coil wiggling a metal armature that moved the blades so would would run -much- faster at 400hz.
I've still got a couple of those cheap old clocks with the synchronous AC motors -- they keep perfect time! I guess if I took one on board and plugged into the shaver outlet, I'd really see time fly. 
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I think EDDT's point was that shavers tend to work as expected when connected to the dedicated 'shaver' outlets. I suspect there must be a 50/60hz inverter on those for this to be the case.
BTW: Trivia point on electric clocks, the power companies don't actually hold 50/60 super accurately, can be a little fast as load goes down etc.
What they do is adjust the frequency so on average the clocks keep perfect time, using their own clock and an external standard.
BTW: Trivia point on electric clocks, the power companies don't actually hold 50/60 super accurately, can be a little fast as load goes down etc.
What they do is adjust the frequency so on average the clocks keep perfect time, using their own clock and an external standard.
I remember seeing a 120V/400HZ sticker in an aircraft lav and wondering about it, long before this thread even started. But things may well have changed, especially in these days of cheap inverters.
Much more recently I read about an experiment they planned on some portion of the U.S. grid, where they would relax the relatively tight existing tolerances on frequency. Apparently, it saves energy if they don't have to pour on the coal (perhaps literally) to hold frequency when the demand surges.
Much more recently I read about an experiment they planned on some portion of the U.S. grid, where they would relax the relatively tight existing tolerances on frequency. Apparently, it saves energy if they don't have to pour on the coal (perhaps literally) to hold frequency when the demand surges.