Purpose of Ground Wires

[abusementpark]

I'm sure this is a very elementary question around here, so please excuse a curious structural guy, but what is the purpose of the ground wires above the conductors in typical transmission lines?

 

[rbulsara]

So that the direct lightning strike will be on the ground wire first, instead of the line wires. Thus minimizing the lightning surges in the lines and resulting equipment damage.

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

What Rafiq said.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[StephenSDH]

I would say the lightning is a secondary purpose of ground wires. The primary purpose is to protect people from shocks. Grounding all Steel, Water Pipe, Rebar, ect. provides a low impedance path for electricity to flow during a fault or lightning strike. Normally there should never be current flow on the ground conductor. When a phase conductor shorts to building steel or water pipe, there needs to be a low impedance path to trip the breaker and clear the fault. Otherwise when you step into the shower or lean against something metal you could be electrocuted if a fault had occurred.

http://www.HearnEng.com

 

[amptramp]

I would say the primary purpose for the "ground wires above the conductors in typical transmission lines", called overhead ground wire or static line, is, as noted by Rafiq and Bill, for lightning surge protection. The static line is installed to provide "umbrella" protection against lightning strikes for the phase wires mounted beneath.

 

[abusementpark]

So, the lightning will first strike the ground wire because it is higher than the other wires? Or is there another reason that the lightning will go to the ground wire first?

 

[alehman]

Because it's higher.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[amptramp]

I would hypothesize the reason a lightning stroke leader will preferentially strike a static line is also that the static line provides a low impedance to earth.

 

[StephenSDH]

Opps. Didn't I read "transmission line".

http://www.HearnEng.com