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High Voltage - Electric Shock Near HV or EHV Busbar

04/28/2010 6:04 AM

Is it a possiblity to get electric shock to a person standing near HV or EHV busbar without touching?

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#1

Re: High voltage hazards

04/28/2010 6:10 AM

Short answer YES
Long answer:- It all depends on your definition of 'near' and if they are grounded.

Del

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#2
In reply to #1

Re: High voltage hazards

04/28/2010 6:22 AM

Can you tell me approx clearance for 110kv.If the person is shocked how? What if he is not grounded,i mean he use a shoe?

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Guru
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#3
In reply to #2

Re: High voltage hazards

04/28/2010 6:33 AM

It's not my field of expertise...
I answered the original question as posed, it doesn't follow that I can answer subsequent ones.
But now the discussion has started, doubtless someone who knows about this stuff will join in.

Google came up with this...
Results 1 - 10 of about 229,000 for "high voltage safety clearance distances". (0.21 seconds)


Del

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#4
In reply to #2

Re: High Voltage Hazards

04/28/2010 8:28 AM

STOP!!! what ever you are doing. Do not work on or around 110kv without on site supervision from a knowledgeable authorized person. Do not rely on safety standards from a web site, even this one. Please look at this video of a 230kv switch.

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#5
In reply to #4

Re: High voltage hazards

04/28/2010 8:44 AM

Just out of curiosity im not supervising.thank you.

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#15
In reply to #5

Re: High voltage hazards

04/29/2010 12:18 AM

NO! He's saying YOU need supervision if you wish to survive!

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#6
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Re: High voltage hazards

04/28/2010 8:46 AM

Wooo, that's cool... that arc looks like the monster from that old 50 sci-fi film forbidden planet?
So I make the safe working distance about 200yards for a scaredy cat like me.
Del (GA from me)

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#9
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Re: High voltage hazards

04/28/2010 10:37 AM

Wrongly replied before kindly forgive me.

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#7
In reply to #4

Re: High voltage hazards

04/28/2010 8:59 AM

Sir i never get scared of what i know but now yes im scared.

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#18
In reply to #7

Re: High voltage hazards

04/29/2010 9:38 AM

Sir, I would submit that it is the things you "know", or rather, the things you THINK you know, that always come back to bite you in the arse. More people have died of accidental gunshot wounds from "unloaded" guns than have been killed (in peacetime) from loaded ones, simply because the people handling them KNEW they were unloaded and started violating safety rules as a result.

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#8
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Re: High voltage hazards

04/28/2010 9:07 AM

Don't ask about shock or at what distance you ll get shock.Neither ever try to experience shot on the basis of calculations. Question you should have asked is about the break down of air or what will be breakdown air gap for 110Kv?

Normally air breakdown at 3200 volts/mm , so for 110kv it will spark at a distance of (110000/3200) . Again its a calculation and must not be tried outside of a sophisticated labs.

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#17
In reply to #8

Re: High voltage hazards

04/29/2010 9:33 AM

And of course that calculation does not take into account things like moisture content of the air, dust content (and dust type) of the air, how well the person is grounded (not all shoes are created equal. Some are better insulated than others and shoes are generally not rated for their breakdown voltage. =b). it also does not take into account any static electrical charge you may have built up either. once the air becomes ionized (once the arc begins) it becomes a low resistance path and becomes a conductor itself. That was why the arc was curling and twisting in the video redfred pointed to. The ionized air was rising due to convection and swirling and the arc was following the path of least resistance.

Bottom line, apply a hefty safety margin to any calculated clearance number you arrive at.

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#19
In reply to #17

Re: High voltage hazards

04/29/2010 9:38 AM

Precisely why my colleague thought he was far enough away to point, but he wasn't.

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#21
In reply to #19

Re: High voltage hazards

04/29/2010 9:50 AM

the air was probably full of ozone and ionized due to corona to begin with which knocked the breakdown voltage way down. again it is the things you THINK you know that will kick your butt.

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#10

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/28/2010 11:37 AM

Yes, air can turn into an electrical conductor. And always remember that "stuff happens."

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#11
In reply to #10

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/28/2010 12:52 PM

Sir, like in the case of lightning arresters(action of sharp points) can a person be a cause for initiating flash and cause an accident?

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#12
In reply to #11

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/28/2010 1:03 PM

Yes, a human being by pointing at a high voltage bus can initiate an arc flash. I have witnessed this. Fortunately for the Physicist knocked down by this arc, the supply was only capable of providing decades of micro-amperes of current. But the fool tried to point to the circuitry three times while saying "That shouldn't happen" before people could stop the experiment and him.

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#13
In reply to #12

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/28/2010 11:11 PM

Your physicist friend was lucky. For current levels below the "can't let go" threshold broken elbows are a common injury from pulling back from a small arc current.

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#25
In reply to #12

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/29/2010 11:30 AM

I think I worked with that guy.

Bill

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#14

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/28/2010 11:51 PM

It all depends on what your definition of "near" is and if you are grounded. To a bird on a high tension wire or a repairman transferring from a helicopter to a high tension transmission wire near is the same as touching, i.e. no problem. AT 75,000 volts/inch for a spark between oppositely charged spheres "near" for me personally is anything less than 20 feet.

The 75,000volts/inch is only the start of the arc, the air begins to conduct electricity with the arc and the distance between the spheres can be increased considerably without increasing the voltage. This is the effect illustrated in many of the old Frankenstein's Monster films

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#20
In reply to #14

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/29/2010 9:46 AM

Old Salt brings up another point that is often not appreciated by people not "in the know". Helicopters and other aircraft (but helicopters especially due to the way they are used in industry) can generate a HUGE static charge from the blades moving past the air. People who work around them for lifting cargo must use a "hot stick" grounding rod to ground the sling hanging from the aircraft before touching it. The charge can be high enough to kill you. Helicopters are often used by power company linemen to place workers ON the HV/EHV lines in order to work on them and that static charge is a factor in how they must work.

you can see static charges discharging from the rotor tips in these pictures as an example.

http://current.com/news/92339989_photos-of-helicopter-static-electric-phenomenon-resulting-in-beautiful-rings-of-light.htm

http://current.com/technology/91538144_helicopter-blades-generate-lightning-bolts.htm

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#22
In reply to #20

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/29/2010 9:57 AM

Notice the next time you see a real helicopter sea rescue. The hoisting basket/sling (depending on the age of the footage) first dips into the water for precisely this reason.

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#24
In reply to #20

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/29/2010 10:03 AM

a video explaining the same:

http://www.youtube.com/watch?v=Qq1W-v7A7Wg

http://www.youtube.com/watch?v=-Zwn2CvwACY

http://www.youtube.com/watch?v=9tzga6qAaBA

http://www.youtube.com/watch?v=7XGaQS1BjaM

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#26
In reply to #14

Re: High Voltage - Electric Shock Near HV or EHV Busbar

05/01/2010 12:25 AM

Thank you sir 75kv is less than 110kv.thats great knowledge.i also studied 16kv/cm is enough for arching in atmosphere.

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#16

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/29/2010 8:59 AM

Only if you're grounded. However this won't protect you from arc blast.

Google NFPA 70E

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#23

Re: High Voltage - Electric Shock Near HV or EHV Busbar

04/29/2010 9:58 AM

Yes if the voltage is high enough. 10,000 V will jump 1" is the old rule I remember.

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