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 Post subject: Alright everyone, I have a question regarding HV powerline shocks.
PostPosted: Sun Apr 08, 2012 4:33 pm 
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Alright so first of all I'm a new member here, so bare with me. I am a college student studying meteorology, so I have a lot of knowledge regarding lightning and how people manage to survive and why. However my knowledge on human power distributions and their specifics is somewhat limited.

Therefore I have a question regarding contact with high voltage power lines, and just human contact with electricity in general that is really bothering me. First off, has anyone seen the video on Youtube "Chinese woman survives 10,000 Volt shock"?

Well I give this warning, this video is a bit gruesome do to the electrical accident involved, in this video a person, I'm assuming mental, contacts a high voltage distribution power line somewhere in China that the video says is 10,000 volts. Based on the insulators and wire spacing this voltage rating seems about right. Either way, it appears to be at least similar to HVAC distribution lines here in the U.S.

Anyways, the person contacts the line with their right hand, and the contraction of the muscles transfers the arc to the head sending the HV arc right into the head. When you see the video in slow motion , it looks like the flow of current exited the body through left hand cause you see a flash of light there as well. What is absolutely driving me crazy is how is it possible for this person to survive a shock like that? I mean it looks like the shock went through the brain and likely through the chest considering entry and exit points, yet later in the video it shows the person regaining consciousness on their own and examining burns from the shock. The burns this person received also seem rather minor considering they contacted a distribution power line. Any case I can think think of where people contacted power lines the burns and injuries are usually much worse than in this case. Yet the shock received appears like it would either most certainly be fatal are at least cause life changing internal injuries and arc burns.


The only thing I can think of is that maybe authorities cut the current load so the person only received the voltage potential. I mean it still looks like a violent shock but it looks more like what would happen if you touched the output of a neon transformer, not a distribution line.

I'm not sure if anyone has seen the video or not, but before you answer my question you should probably see the video. At any rate, I'm confused how the person survived with relatively minor injuries considering what happened.


Furthermore this question also covers just high voltage shocks in general, I'm familiar with what amounts of current it takes to kill a man, and I'm very familiar with the relationship between voltage and current and I realize that HVAC transmission lines have plenty of current, not just voltage which in total watts should be overkill for any person I would think. That being said I've heard of people breaking into substations hoping to steel copper and contacting transmission line voltages of as much as 100,000 volts and still surviving, albeit with severe injuries. I've also heard of people dying from these shocks too, but still how is it that some people seem to be be burned alive or explode from high voltage contact while other live to tell and make full recoveries from contacting such extreme amounts of electrical energy?


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PostPosted: Mon Apr 09, 2012 8:24 am 
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Ryan- Your amazement is well-founded. This type of accident is typically fatal. I don't think that there is a good explanation for her survival. It would be interesting to find out what happened to her subsequent to the accident. It would not be surprising to find out that she died soon after. Although the outward injuries appear minor, it is highly likely that she sustained massive internal injury. I agree with most of your assessment. The HV appeared to have several entry and exit points- both hands and head. Additionally, she was closely and directly exposed to the arc flash, which would be expected to cause severe or fatal burns. Notice that her hair is not even burned. Hard to explain. As far as the utility being able to dial down the current; no, that just does not happen. There is more than enough current in that system to be lethal.


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PostPosted: Mon Apr 09, 2012 5:49 pm 
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Had an electrician (fired immediately after) survive an encounter with a 4160 V control power transformer on the primary side about a year ago. He walked away with minor burns on the back of his hand and near his elbow. Granted this was a very special case because we had a high resistance ground fault system in the main substation which pretty much instantly reacted. It kept the current to 25 A maximum and tripped out within about 50 milliseconds so his arm didn't have much of an opportunity to reach the well done state anyways.

As the voltage increases, it is not typical that someone actually TOUCHES the conductor. Before you heat it up to the point where it is a plasma, the resistance of air is approximately 3x10^6 V/m, but obviously the shape of the electrode, humidity, pressure, and other factors affect the initial arc, and then it drops down to around 150 V once the air has gone to plasma state as the temperature rises.

Another major factor that occurs is that sometimes the arc will travel across the surface and not necessarily penetrate as much as would be expected to happen, at least initially.

And I've also heard of cases where it is conjectured (but not proven of course) that the force of being knocked away was enough to restart someone's heart.

And since you've seen the lightning data, you also know that it is not uncommon for someone to appear normal at least initially and then have major neural problems or die shortly after exposure.

So...when it comes to shock, regardless of whether it is due to lightning, DC, or AC, at almost any current and voltage combination, you just really can never be too sure of what the ultimate outcome is.

At the very low end however, shocks are generally survivable. Google for Dalziel. He did some incredible work in the 1950's that gave us all that we use today in terms of shock protection. MSHA has apparently even accepted the idea that with a reasonably fast trip relay at relatively low voltages (even up to 100 V), you can safely shut down a DC system before the victim goes into cardiac arrest. Right now 70E (and most other safety codes) cut off at 50 V, but there are known cases (welders in particular) where this cutoff is still not low enough. I think MSHA has the right idea in using both voltage and time to determine what is safe.


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PostPosted: Tue Apr 10, 2012 4:49 pm 
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Thanks for answering my question!

Well the reason I know as to why people survive lightning is the fact that the lightning strike is extremely quick, in fact it occurs for a much more brief amount of time for our eyes to even follow, that being said it never has time to transfer much energy into the body, and that many times it travels around the outside. There is a more rare type of lightning known to be positive stroke lightning by which current flow occurs for slightly longer, long enough that at many millions of volts and thousands of amps has killed people in a horrific manner. Although still very brief, enough to keep the body recognizable from what I know. But really, with lightning, its the extreme short duration that keeps most of the energy from actually being transferred into the human body, which explains why all humans just don't get friend immediately from the shock. Positive stroke lightning is also9 responsible for serious forest fires and destroys and also causes fires that often lead to complete loss of a structure on impact. It has been found that about 70% of victims actually survive lightning because of what I stated above. Although most strikes are highly indirect which explains some of that as well.


Anyways, off the lightning subject. I do agree that source the person contacted certainly contains well more than enough current to kill, but it also looks like the arc flash isn't as intense as often occurs with contacting power lines, meaning amazingly that person body allowed relatively low current flow considering available current. I could be wrong but the arc flas doesn't look as bright or intense as many incident I've seen, in the slow motion it does but that is because its slow down, real time doesn't look quite as terrible.


Even still though I do agree about the internal injury factor, lack of external burns may actually mean more severe internal injuries. Sometimes right after the scene an injury may not seem as bad until medical evaluations and vise versa when it comes to electricity.


I did notice later on as rescuers were lowering the persons body that the person seemed very limp and weak, so as you have suggest the injury may be much more severe internally despite external appearance.


I am still amazing by the outcome either way, my dad is an electrician and he knew a man that got too lazy with his job and decided to flip a switch above a transformer while standing on the edge of the bucket, he fell into the lower phase line that was around 12000 volts with his upper body while contacting the transformer with his lower body and the wooden pole, terrible accident. It was known that parts of him literally "exploded" while being enshrouded almost entirely in the arc flash.

I guess electricity does a different thing to some degree every time. After all, voltage does mean electrical potential. Either way, the higher the voltage, the more dangerous and destructive the shock as long as there is a good available current source.

I had an incident where I was clamped to a 120 volt 5 amp Christmas light set when I was a young kid(dumb and young) for many seconds(I nearly lost consciousness so I don't remember exactly how many). While others have been killed from the some event, I recovered without hospitalization, so I have been on the fortunate end of electrical accidents my self.



Well anyways, thanks for the input everyone! If anyone else wants to comment on this strange electrical accident, please do!


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PostPosted: Tue Apr 10, 2012 4:57 pm 
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4160 volts at 25 amps for that duration is still something I would never want to experience! I have contacted a 3000 volt bug zapper, and even with minimal current that shock felt like a baseball slugger slammed my hand with a baseball bat.


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PostPosted: Tue Apr 10, 2012 5:52 pm 
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Quote:
Anyways, off the lightning subject. I do agree that source the person contacted certainly contains well more than enough current to kill, but it also looks like the arc flash isn't as intense as often occurs with contacting power lines, meaning amazingly that person body allowed relatively low current flow considering available current. I could be wrong but the arc flas doesn't look as bright or intense as many incident I've seen, in the slow motion it does but that is because its slow down, real time doesn't look quite as terrible.


This is actually true for a couple different reasons. Almost all utility faults are line-to-ground (90%) due to the large distance normally between phases. Line to ground voltage is 1.73 times lower than line to line in a delta-wye system. When contained inside switchgear, the copper vapor which is just as conductive as the solid form usually elevates the arcing fault quickly into a 3 phase arcing fault regardless of the initial starting condition. Second, the very long line lengths typically result in much smaller available fault currents compared to short buses in an industrial operation. Third, open air arcs radiate energy in a spherical pattern. In a power distribution panel on the other hand, the metal sides reflect the radiation and concentrate it to roughly 3 times the open air result. Fourth, arcs on utility lines are often magnetically propelled away from the fault location like a Jacob's ladder so the time of exposure can be noticeably decreased by this effect if the arc itself is relatively transient. If you check YouTube, there is an interview from a representative from EPRI that talks about some of the differences that EPRI's tests have shown relative to the test data set that IEEE 1584 is based on.

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4160 volts at 25 amps for that duration is still something I would never want to experience! I have contacted a 3000 volt bug zapper, and even with minimal current that shock felt like a baseball slugger slammed my hand with a baseball bat.


Quite the opposite though I wouldn't want to try to test this. The 25 A is only if the resistance of the would-be victim is zero. Actually resistance grounding systems reduce step and touch potential hazards to a known, engineered, and controlled minimum:
http://www.msha.gov/S&HINFO/TECHRPT/GROUND/SAFETYGR.pdf

I misspoke. In this case the victim was standing on the substation frame ground, not the safety ground, and his elbow touched the safety ground, which was just plain dumb luck. If he had only touched the safety ground, he would have walked away unharmed.


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PostPosted: Tue Apr 10, 2012 7:39 pm 
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Yes, that's true, due to body resistance a person wouldn't allow all 25 amps to flow. However at 4000 + volts its certainly going to be more than typical contact with other 20 to 30 amp sources that are usually in the 200 volt range. The most intense low voltage shock I've ever received was when I was using a 12 amp vacuum cleaner that was getting old, the motor also was fried from the incident.


Anyways, that's a great link, thanks for the info!


BTW, one other thing that confused me, when it comes to high voltage, wouldn't somebody who has a higher body resistance have more physically visible burns, and someone who has a lower resistance get more severe internal injuries? So its possible that a body with higher resistance would look more injured from the outside, and someone with lower resistance would look less injured from the outside but might have suffered much worse internal damage from higher current flow? With this question, assume the voltage and current induced, as well as duration is the same, in both the higher resistance person and the lower one.

The reason I ask this is that I know that I know when it comes to lower voltage, if the resistance is high, then you get in general a weaker shock( less current flow). However, with high voltage( 7 kV+ with power line systems) wouldn't the high voltage against the bodies resistance cause more visible exterior burns to the skin due to thermal energy being put into the body? Or does resistance not work that way?

I'm relating that to how my electric oven coil gets red hot because it resists electrical flow significantly but still allows current flow thus transferring electric energy into the coil causing the temperature to soar.


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PostPosted: Tue Apr 10, 2012 7:47 pm 
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Actually sorry about the current induced part, what I meant to say was assuming both arcs hitting each body of different resistance have the same amount of current and the line voltage is the same.


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PostPosted: Wed Apr 11, 2012 4:49 pm 
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Quote:
BTW, one other thing that confused me, when it comes to high voltage, wouldn't somebody who has a higher body resistance have more physically visible burns, and someone who has a lower resistance get more severe internal injuries? So its possible that a body with higher resistance would look more injured from the outside, and someone with lower resistance would look less injured from the outside but might have suffered much worse internal damage from higher current flow? With this question, assume the voltage and current induced, as well as duration is the same, in both the higher resistance person and the lower one.


Your questions can probably best be answered by the book by Dalziel. He spent lots of time studying this. There are charts quoted from his book and the vast majority of discussion of shock hazards in IEEE standards comes from Dalziel's work.

As to physical burns, I have no idea. Suffice to say that I'm not really interested in the morbid details of how a co-worker gets fried. I'm far more interested in how to avoid this in the first place, just as I'm far more interested in how to design equipment to be lightning resistant.


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PostPosted: Sat Apr 14, 2012 10:01 am 
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PaulEngr wrote:
Your questions can probably best be answered by the book by Dalziel. He spent lots of time studying this. There are charts quoted from his book and the vast majority of discussion of shock hazards in IEEE standards comes from Dalziel's work.

As to physical burns, I have no idea. Suffice to say that I'm not really interested in the morbid details of how a co-worker gets fried. I'm far more interested in how to avoid this in the first place, just as I'm far more interested in how to design equipment to be lightning resistant.




Thanks, and my reason for wanting to know about physical burns comes down to safety as well. I don't want to know the details on electrical burns just for the sake of it(that's just gross). Rather, there is a lot of confusion out there amongst electrical knowledge. I've heard some people assume that if there body has a higher resistance to current they would be more likely to survive more powerful electric shocks. For example, my dad who is an electrician knows someone who seems to have a much higher than normal resistance because he has know problem grabbing a hot 120 or 240 volt wire and also grabbing a ground at the same time. Apparently he has a rare physical condition( there is a man famous on Youtube in India who has a similar condition) that makes him more resistant to current flow or something like that.

Anyways, the guy thinks that because of that he could probably take high voltage shocks too with no problem, although the fact that he hasn't attempted to(thankfully) yet is good, because he probably knows better. But anyways, I just wondered that higher than normal resistance to lower voltage could prove more deadly for higher voltages that "don't pay much attention" to skin resistance.


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PostPosted: Sat Apr 14, 2012 10:02 am 
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no problem*


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