Why does 25Kv do much more harm that 50Kv in these cases?
ScottH, Wed Mar 08 2017, 08:57AMI know a persons body resistance varies, but a 50Kv power line has 2x the voltage of a 25Kv train line. I don't know if I am allowed to post those videos on here, but you can look it up on YouTube if you want.
I saw a video of a guy touching a 25Kv line while standing on top of a train. He was instantly burned to a crisp and was on fire with just one touch.
I also see videos where people who climb up on poles touch a 50Kv wire, it makes the arc flash, then they fall (if not strapped). For some reason they appear to receive much less damage, compared to the guys on the trains. A lot of the 50Kv power line victims survive, but the other cases of people who touch the 25Kv train lines always result in them getting fried instantly, even if some survive with 2nd-3rd degree burns over 90% of their body.
Why is this? It has do be more than just body resistance alone. Can somebody please elaborate? A power line/transmission line has to carry more amperes than that of an electric train's power line.
Re: Why does 25Kv do much more harm that 50Kv in these cases?
KrowBar, Wed Mar 08 2017, 03:33PM
You could model each instance, but you would have to have detailed information about the system - In the cases you are referring to, the difference likely comes down to the return path. standing on a metal train roof that has near 0 resistance to ground is quite different then being on a wooden pole which may have resistance many times higher than the body. It's all in the details, but the end difference is primarily how much energy was converted to heat by the body - this will be affected by power and duration, where what looks like a "split second" in both cases could actually be a millisecond in one case and 0.1 s in another case, where 100 times more energy is dissipated if the power is the same.
KrowBar, Wed Mar 08 2017, 03:33PM
You could model each instance, but you would have to have detailed information about the system - In the cases you are referring to, the difference likely comes down to the return path. standing on a metal train roof that has near 0 resistance to ground is quite different then being on a wooden pole which may have resistance many times higher than the body. It's all in the details, but the end difference is primarily how much energy was converted to heat by the body - this will be affected by power and duration, where what looks like a "split second" in both cases could actually be a millisecond in one case and 0.1 s in another case, where 100 times more energy is dissipated if the power is the same.
Re: Why does 25Kv do much more harm that 50Kv in these cases?
ScottH, Thu Mar 09 2017, 05:01PM
Why do both scenarios make a big bright arc to the body and a loud bang? Doesn't it mean a very high current flow in both cases? Is it comparable to lightning, where the current flow is nanoseconds vs touching a trains power line, but we see the same quick flash/boom that has 0.1 sec of current flow?
ScottH, Thu Mar 09 2017, 05:01PM
KrowBar wrote ...
You could model each instance, but you would have to have detailed information about the system - In the cases you are referring to, the difference likely comes down to the return path. standing on a metal train roof that has near 0 resistance to ground is quite different then being on a wooden pole which may have resistance many times higher than the body. It's all in the details, but the end difference is primarily how much energy was converted to heat by the body - this will be affected by power and duration, where what looks like a "split second" in both cases could actually be a millisecond in one case and 0.1 s in another case, where 100 times more energy is dissipated if the power is the same.
You could model each instance, but you would have to have detailed information about the system - In the cases you are referring to, the difference likely comes down to the return path. standing on a metal train roof that has near 0 resistance to ground is quite different then being on a wooden pole which may have resistance many times higher than the body. It's all in the details, but the end difference is primarily how much energy was converted to heat by the body - this will be affected by power and duration, where what looks like a "split second" in both cases could actually be a millisecond in one case and 0.1 s in another case, where 100 times more energy is dissipated if the power is the same.
Why do both scenarios make a big bright arc to the body and a loud bang? Doesn't it mean a very high current flow in both cases? Is it comparable to lightning, where the current flow is nanoseconds vs touching a trains power line, but we see the same quick flash/boom that has 0.1 sec of current flow?
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