Earth as only neutral

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karl riley

Senior Member
I have been told that in Utah and Alaska there still are power lines going to remote areas where the earth is used as the only neutral return path, obviously to save the cost of the neutral conductor.

I asked the electrical engineer (mining) how they overcame the impedance of using the earth path. He mumbled something about adjusting the voltage and went to another topic.
OK, I am told that studies show that earth itself has a negligible impedance due to the infinite available return paths, all in parallel. So the impedance is from the grounding electrode to earth. So to lessen this impedance one could have an extensive system of electrodes at the remote location to lower impedance.

But what about raising the neutral voltage to overcome the remaining impedance? Would this not occur automatically at the remote location? And would it not present a hazard to humans if they stand on the ground and touch a neutral connection?
Opinions? (I am writing a chapter on earth conductivity and need to get some feedback).
Karl
 

bennie

Esteemed Member
Re: Earth as only neutral

Karl: SWER transmission systems are in use today. (Single Wire Earth Return).

Some foreign countries are still installing them.

The principal of operation puts a new spin on grounding.
 

bennie

Esteemed Member
Re: Earth as only neutral

I often get in trouble over my viewpoint regarding the popular accepted theory of touch potential.

The first question asked concerning a SWER system is...What happens if you touch the return wire of a 12 KV system?
 

bennie

Esteemed Member
Re: Earth as only neutral

Hello Scott: The intertie starts here, near Portland, at Bonneville Hydro Plant. I have worked at the Dam.

There is a big upgrade going on now with the rectifiers.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Earth as only neutral

I am just guessing here, but wouldn't the fact that the earth is a somewhat large conductor make up for poor conductivity?
 

bennie

Esteemed Member
Re: Earth as only neutral

You are correct, the cross sectional area makes for low resistance and resultant high conductivity.

Somewhat like paralleling a number of high resistors, eventually the total conductor resistance is very low.
 

dereckbc

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Location
Plano, TX
Re: Earth as only neutral

Karl, you hit the nail on the head, economics.

As far as the touch potential problem you refered to should not be a problem at the remote location as the voltage drop would be spread out from the sub-station to the remote location. It would be high, but impossible to come in contact with due to distance.

[ March 15, 2003, 12:41 PM: Message edited by: dereckbc ]
 

bennie

Esteemed Member
Re: Earth as only neutral

Touching the conductor at the ground connection is the same as touching the neutral buss in a service panel. There is no danger under normal operation. Just don't disconnect it when energized.

The principal is the same as the MGN becoming disconnected at some point ahead of the transformer. High voltage will appear on the neutral.

This leads to the reason for switching all conductors from the utility during a power outage, at the transfer switch.
 

karl riley

Senior Member
Re: Earth as only neutral

I just got to check on the replies. It sounds like the questions have been answered.
Since this is the same as having an open neutral, I would think the touch potential from neutral bus to earth at the remote site would be a function of the grounding system impedance there. No?
I am not so interested in the touch potential as I am in having it verified that this is a workable system. It backs up the university guys who say earth has a negligible impedance. (After you get past the electrode-to-earth impedance).
I will check the reference. I'll print this out so I can remember your names. Bennie, I do remember you from when I last tried to stay current with the forum. Welcome back.
Karl
 

don_resqcapt19

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Illinois
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retired electrician
Re: Earth as only neutral

I don't have my IEEE green book here at home, but I think that the voltage drop in the area within the first few feet of the grounding electrode is over 50% of the total drop. It is in this area that the earth's resistance is the highest, because the current hasn't been able to spread out accross a large area.
Don
 

bennie

Esteemed Member
Re: Earth as only neutral

When determining touch potential, the surface resistance, of the terrain, is a major factor. It is, of course, an unknown variable.
 

charlie

Senior Member
Location
Indianapolis
Re: Earth as only neutral

WOW, this is really an interesting discussion. We do basically the same thing, but differently.

Our transmission lines are fed from delta/wye transformers. We take the wye secondary to the next set of transformation to feed another delta wye transformer . . . then we hit the distribution substation and another delta wye transformer. Up to this point, we do not use a neutral on the primary side of the transformers but we do use static lines to protect the transmission and sub-transmission lines from lightning.

At the distribution substation, we take a multi-grounded neutral with the phase conductors. The NESC requires four grounds per mile on the neutral that are independent of any customer grounds. We still have a little problem with stray voltage but that is another topic.

We used to use series street light circuits with constant current regulators. Sometimes, a system neutral was not available at the end of the circuit. At that point, we would put in three ground rods in a triangular configuration and use the earth as a return (bad idea but we did it). We have eliminated all the series street light circuits from our system now due to their inherit danger. Even though the lamps only had about 90 volts, in the event of an open circuit, the voltage was around 2500 volts since the constant current regulator was trying to push 6.6 amperes.
 

karl riley

Senior Member
Re: Earth as only neutral

There is a wealth of info among these forum members! Bphgravity, thanks for the reference to the Australian SWER site. It was sparse on the technology, but mentioned using copper-clad steel ground rods for the primary Tformers but not how many they use at each 12.7kv Tformer.

The voltage between the grounding electrode conductor and earth would be V=IR. So if the transformer is supplying 100 A, and they have their ground rods down to, say, 5 ohms in parallel, the voltage drop would be 500V. So the grounding equipment would have to be insulated just like a hot conductor. This is my take on the logic. Any experienced comments?
 

bennie

Esteemed Member
Re: Earth as only neutral

No one believes me but here goes... This is the same condition as working live power lines bare handed. I was a combination lineman/wireman in my work days.

The terrain around the electrodes charge to the 500 volts. There is no difference in potential from the ground rod and the terrain.

Like I wrote "this puts a new spin on grounding"
 

bphgravity

Senior Member
Location
Florida
Re: Earth as only neutral

So, is the idea to get ground impedance so low that natural human resistance will be so high in comparison that there becomes no potential for current to flow through the body? Or is it that the service equipment, the grounding equipment, and the earth all have the same potential, therefore no possible way to conduct electricity through the body? Almost the same thing, but not exactly. Also, how does the main trip during a fault when there is no direct grounded connection back to the transformer?
 

don_resqcapt19

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Location
Illinois
Occupation
retired electrician
Re: Earth as only neutral

Look at Mike's article Ground Rod does NOT Reduce Touch Potential. If the total voltage drop is 500 volts then someone touching the grounding electrode conductor and the earth 1' away from the grounding electrode would be sujected to 340 volts. Yes, the current through the human will be limited by the persons impedance, but 340 volts is more than enough to cause a fatal amount of current to flow through the body. Even someone standing on the earth near the electrode with his feet a foot apart could be sujected to a fatal shock.

Bennie,
Are you telling us that you worked live lines while grounded?????

Don
 

bphgravity

Senior Member
Location
Florida
Re: Earth as only neutral

Thank you for that link, Don. This information is what I thought. A few years ago, a boy touched a light pole and the frame of a bus stop enclosure and was electricuted. Apparently, the metal enclosure was grounded better than the light pole and used the boys body. So, this brings me back o the question of how do these conditions exist safely on these SWER systems? This is not like a bird on a high wire anology. If I am grounded, or I am touching something that has less resistance than the grounded system, the current can and will flow through me. Bennie, can you explain your theory in more detail?
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: Earth as only neutral

Bennie, I believe you. Used to work for a electric utility, and seen it done on a daily basis. If memory serves me correctly it is done on transmission lines configured as delta. As long as the platform or bucket truck is insulated you can do it.

I also read and seen several utility's working on 750 KV lines with helicopters and the lineman on a platform attached to the helicopter. You couldn't pay me enough to do it.
 
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