An Accident

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Sahib

Senior Member
Location
India
Recently in Tamil Nadu, an Indian State, a husband and wife and their two children aged 1 and 11/2 years were electrocuted, while travelling in a motorcycle, when a 11 kV high voltage overhead power line broke and fell on them. I wonder how this could have happened. The neutral of the HV line is grounded at the substation and earth guard is provided at pole cross arms. So before the snapped HV line could touch the victims and cause electrocution of them, it would have been grounded by the earth guard at the pole cross arm and rendered harmless. But, sadly, this was not what happened. I do not know where things could have gone wrong to have caused this mishap. Please comment.
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Electrical Contractor
I see hot wires sitting on the ground all the time but I am unfamiliar with this earth guard at the cross arm. What and how does this function- or suppose to function in this case.
 

Sahib

Senior Member
Location
India
I am unfamiliar with this earth guard at the cross arm. What and how does this function- or suppose to function in this case.
A mesh like pattern of bare wires below the HV overhead lines and connected to the pole cross arms at ground potential So if any HV line breaks, it first comes into contact with this and so grounded before it is able to fall to ground below. But in the newspaper report below, the utility Engineer makes no mention of it!
http://www.thehindu.com/todays-paper/tp-national/tp-tamilnadu/four-of-a-family-electrocuted/article4819213.ece
 

Sahib

Senior Member
Location
India
Is it possible for the wire to snap right before the protective guard and fall to the ground without hitting the arm?
No. Because the protective guard wire mesh tied to the cross arm and hung below the 11kV lines is connected from pole to pole.

From the statement of the utility Engineer in the Newspaper report, it is apparent that no such protective guard was provided in this case: a fatal lapse on the part of the utility.
 
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don_resqcapt19

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Staff member
Location
Illinois
We don't have any type of protection like that in the US. On a typical transmission or distribution sytem the conductor that is connected to earth is intalled above the other conductors. About the only time you will find the grounded conductor below the high voltage conductors is where the secondary conductors for the distribution transformers are run on the same poles and they have used a single conductor as the grounded conductor for both the primay and secondary systems.
 

don_resqcapt19

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Location
Illinois
Don:
Then what is done in US to render snapped HV line dead before it touches ground? Thanks.
Nothing...they are often live on the ground. There may be enough ground fault current to trip the OCPD, but then again there may not be. Also even if it does trip to start with, there are often re-closers on the line that with restore power 2 or 3 times before it locks out.
 

GoldDigger

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Staff member
Don:
Then what is done in US to render snapped HV line dead before it touches ground? Thanks.
Basically, in the US high voltage lines are not as often strung above and across streets and public right of way, so the results of a broken line are not as severe.
There may also be some differences in maintenance and design which results in fewer downed lines.
Most are the result of wind storms or fallen trees or operational error by cranes and other equipment rather than spontaneous failures.

When temporary high voltage lines are placed across a highway during construction, protective guards are often used, but I could not tell while driving by whether they were ground grids or just insulating nets.
 

PetrosA

Senior Member
Basically, in the US high voltage lines are not as often strung above and across streets and public right of way, so the results of a broken line are not as severe.
There may also be some differences in maintenance and design which results in fewer downed lines.
Most are the result of wind storms or fallen trees or operational error by cranes and other equipment rather than spontaneous failures.

When temporary high voltage lines are placed across a highway during construction, protective guards are often used, but I could not tell while driving by whether they were ground grids or just insulating nets.
Huh?!? California must look a lot nicer than the East Coast then. I don't take my camera out very often anymore since I moved back the to the US specifically because there are so few chances to get a landscape shot without dozens of wires (HV, LV, TEL and Cable) in the picture. In elementary school we had guys from the POCO come in to give us lessons on what to do when a high voltage line came down on the car. I don't think you can say that we don't "often" string primaries above roads at all, especially in the 12 kV and lower range.
 

edward

Senior Member
I do have overhead bare primaries going across my back yard fence.

Although, some communities will not allow ANY over head lines. Even when you do a panel upgrade and it is existing over head you have to go under ground.

Other than mother nature, I believe it is lack of good design & lack of maintenance in the OP case.
 

GoldDigger

Moderator
Staff member
Huh?!? California must look a lot nicer than the East Coast then. I don't take my camera out very often anymore since I moved back the to the US specifically because there are so few chances to get a landscape shot without dozens of wires (HV, LV, TEL and Cable) in the picture. In elementary school we had guys from the POCO come in to give us lessons on what to do when a high voltage line came down on the car. I don't think you can say that we don't "often" string primaries above roads at all, especially in the 12 kV and lower range.
Yes, California does look a lot cleaner in terms of wires. But mostly because new suburb construction used underground wiring. From what I have seen in random pictures from India, both HV and LV lines in urban areas cross streets or run above sidewalks a lot more than in most of the US.

When I was last in Bangalore, half the street light poles on the main road to the airport had exposed wires going through holes broken in the cast iron bases of the poles, apparently bypassing defective wiring under the poles. In the main shopping district, every 10th store had a generator at the curb with individual wires running exposed across the sidewalk and in the front door.

The main business streets in the high tech office area had unfilled ditches in the dirt alongside the pavement where fiber optic links had been installed two years earlier.

Not judging the society, just describing the normal sate of electrical infrastructure at that time (about 8 years ago.)
 
Location
Mumbai India
Occupation
Electrical Consultant
No. Because the protective guard wire mesh tied to the cross arm and hung below the 11kV lines is connected from pole to pole.

From the statement of the utility Engineer in the Newspaper report, it is apparent that no such protective guard was provided in this case: a fatal lapse on the part of the utility.
Dear Sahib Sir,
In Maharashtra state similar cases are reported. Still the authorities are negligent about the unsafe situation leading loss of precious life. An appropriate guarding with mesh formation would provide safety at road crossing and footpaths.
Thanks,
Bhushan , Bachelor Of Electrical Engineering
 
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