Ground Wire in Transmission/Distribution Systems

[QwertyXP]

Does the ground wire used in transmission/distribution systems also serve as a neutral wire in some cases or is it used only to protect the conductors against lightning strikes?

 

[Crazymechanic]

This is different in different parts of the world , in Europe atleast the ground wire is not tied together with neutral.
Neutral serves as the return for the hot wire, live wire.The ground wire serves as a low resistance path for a fault current to drain.Like in the case of a faulty isolation of a wire in a water heater or washing machine etc.Yes it can also save lives in the case of a lightning strike if it hits the device and destroys the internal isolation so that a voltage appears on the device chassis which can come in contact with you.

for more answers see this recent thread.

https://www.physicsforums.com/showthread.php?t=722911

 

[rp55]

My understanding is that in the US, neutral is connected to ground at the home entrance coming off the pole. The reason this works is because Neutral (the so called "negative" in ben franklins conventional current) will be flowing FULL amps and zero potential back to the source (voltage being a must have for current to flow unless it's already on its way at the speed of light... but if it picks up a load it will become > 0), while the separate ground wire coming from your toaster body to that same outside Neutral/Ground connection will send any short via the body to ground uninterrupted because that wire has no potential before the short. It was previously an open circuit. Once you close that previously open ground "non-circuit" then it has potential.

 

[rp55]

And the transmission ground tap is a "floating" tap for transmission lines in my understanding. It is not "ground" per say, but a reference to the other lines. Hence localization via the inducted voltage via transformer near the home which being sent to ground, and not the transmission line "ground". That near home true ground is likely the source of lighting protection to the transmission source. Lightning is Earth to ground potential. That potential could affect local house ground potential (it often does and blow stuff up) as well as affect transmission line "grounds". Again I'm speculating and would be curious to hear an expert opinion.

 

[QwertyXP]

I was actually referring to the wire running above the phase conductors between the the poles of a transmission system and not the one used in house wiring systems:
http://en.wikipedia.org/wiki/Ground_wire_(transmission_line)#Ground_wires

The Wikipedia articles says something about the ground wire serving "as a parallel path with the Earth for fault currents" in circuits with earthed neutral, but it doesn't seem to answer my question.

 

[Crazymechanic]

Well firs of all in US the house wiring indeed has the neutral to ground.
In other parts of the world the ground wire is a independent wire and should not be connected together with neutral.

And thirdly the wire which runs on the high power transmission lines is not a ground wire but the neutral wire.
Most of the high voltage line polls are metallic so they act as one big ground wire , if any of the wire should snap and hit it that would be the closest path to ground.
Also in modern days there are sensors at distribution stations which cut the voltage if they sense a fault somewhere in the line , like a cable snapped and fallen on ground or similar.

 

[nsaspook]

Well firs of all in US the house wiring indeed has the neutral to ground.
In other parts of the world the ground wire is a independent wire and should not be connected together with neutral.

And thirdly the wire which runs on the high power transmission lines is not a ground wire but the neutral wire.

On most of the long AC high-voltage transmission lines in this part of the country the top wire is a ground to protect the power lines from a direct hit. On a medium voltage three-phase local distribution line the top wire is usually one of the phases. With normal (Delta configuration) three-phase distribution there is no need for a neutral. The neutral is created with a Wye (or Star) configuration transformer at a site sub-station or pole.

 

[dlgoff]

The geometry of the conductors and earth-wire determines the Electric and Magnetic Field strengths around the lines. e.g.

400 V lines are mostly carried on wood poles with four (or sometimes five) wires in a vertical array. The bottom wire is an Earth wire which screens the fields produced by the wires above it, making electric fields from 400 V lines very low.

http://www.emfs.info/Sources+of+EMFs/Overhead+power+lines/specific/400+V+overhead+electric.htm

 

[nsaspook]

http://books.google.com/books?id=9k...sO2iwKvsoCYBw&ved=0CDgQ6AEwAg#v=onepage&q=400

400V/230V is the secondary distribution system after the primary distribution delta to star conversion and neutral creation.

 

[QwertyXP]

Thank you all, and specifically, nsaspook.