How does the typical mains power connect in the USA anyway?

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bud-- wrote:

I haven't been in a rural enough area in years to even look for one. The fact that it isn't common doesn't mean that it doesn't still exist. Some farms were 20 miles from the nearest highway, on a private dirt or clay road. They were electrified by either a co-op or the TVA and 20 miles of copper wire was expensive.
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On 11/26/2013 01:28 PM, Michael A. Terrell wrote:

"Many national electrical regulations (notably the U.S.) require a metallic return line from the load to the generator. In these jurisdictions, each SWER line must be approved by exception."
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dave wrote:

Yes, the ground resistance has to be low enough to prevent gradient voltages from killing people or animals.
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On 11/25/13 5:33 PM, Danny D'Amico wrote:
Cut a bunch to keep AIOE happy.

Article here http://preview.tinyurl.com/mxd4xb2 talking about power distribution. It was written by a fella with a BSEE and an MSEE. He spent a bunch of years working in the power industry. He writes about a possible project in Alaska. Single wire earth return similar to what the Aussies do.
He says: A single wire, ground return circuit will require a waiver from the Alaska legislature or Department of Labor since it does not comply with the NESC. However, the author does not believe that the single conductor, earth return circuit should be considered and firmly believes that a multi-grounded, neutral be considered on all single phase and three-phase, four-wire circuits. End quote.
The fact that using the earth return system requires a waiver implies that it is used very infrequently.
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On Tuesday, November 26, 2013 6:59:17 PM UTC-5, Dean Hoffman wrote:

Nice find. I concur with your assessment. And I'd say a paper from an IEEE fellow trumps "How stuff works".
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On Monday, November 25, 2013 3:18:49 AM UTC-5, Danny D'Amico wrote:

Most of the current doesn't have to flow back via the earth. You have a transformer that is connected on one phase of the primary. It serves several houses. Further down the street, there is another transformer, it is on a different phase. Even further down, there is another transformer on the third phase. The other sides of all those transformers are all tied together on the primary neutral. If those loads are equal, then the sum of the currents in the neutral is zero, you have a balanced wye configuration and the only net current flow is in the 3 primary phase wires.
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On 11/25/2013 2:18 AM, Danny D'Amico wrote:

The earth does not complete the circuit. Wires complete the circuit.
The electrons that flow are in the wire.
If you had DC, an electron flowing out one end of a wire would be matched by an electron flowing in the other end. A single electron may not move very far, it can be replaced by another electron. A property of a metal is that there are electrons that are not tightly bound that can migrate.
With AC, electrons move in one direction, then the other.

The do have a wire for any intentional electrical path.

Since early power distribution days there is a metal connection for the entire path. Earth is not an intentional path.

The earth is not used as an intentional path.
The connection to earth is used to limit the voltage between the wires and the earth. The earth is also a sink for lightning and similar events, and is used to trip overcurrent protection with crossed wires.
The earth is not allowed to be a path to trip a circuit breaker in your house if there is a short between a hot wire and ground at, for instance, a drill. The short circuit current goes through the N-G bond at the service and returns to the utility transformer through the service neutral. The earth is not allowed to be the path because it is not an effective path.

Rather flawed.
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bud--;3155057 Wrote: >

Bud, until recently I would have agreed with you. But, whomever wrote this web page obviously knows something about electric power generation and distribution and seems to disagree:
http://tinyurl.com/y4syno6
Look at the bottom paragraph in the section entitled "The Power Plant: Three Phase Power" where it says:
And what about this "ground," as mentioned above? The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons. (Car manufacturers do something similar; they use the metal body of the car as one of the wires in the car's electrical system and attach the negative pole of the battery to the car's body.) "Ground" in the power distribution grid is literally "the ground" that's all around you when you are walking outside. It is the dirt, rocks, groundwater, etc., of the earth.
I don't think he could have said it any clearer.
--
nestork


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On Monday, November 25, 2013 2:43:01 PM UTC-5, nestork wrote:

And just before that, the author, said:
"There are four wires coming out of every power plant: the three phases plus a neutral or ground common to all three."
That sentence alone shows that he doesn't know what he's talking about. A netural or ground wire are not the same thing. And even if they were, if the earth were used as the return path, then why would you need the 4th wire? The 4th wire carries the unbalanced current. The current is flowing in the 3 phase wires and neutral, not the ground.
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On Mon, 25 Nov 2013 20:43:01 +0100, nestork

And he COULD have been more accurate. He is wrong, for instance, in stating each tap takes off 2 phases. It GENERALLY takes off ONE phase - which feeds a center tapped step-down distribution transformer. The primary of that thansformer has only 2 conductors, and a single winding. The secondary has 3 wires, and a center tapped winding, providing SINGLE PHASE power to the local residential grid.. There are 2 basic 3 phase connection schemes, delta and wye. Wye has a neutral (so requires 4 wires) while delta uses only 3 wires. Delta connections take power from l1 to l2, l2 to l3, and l3 to l1. Wye takes power from l1 to n, l2 to n and l3 to n.
BOTH are used. A 3 phase generator can be either delta or wye. In North America MOST systems are wye, while in other parts of the world delta is more common. (but in europe, 4 wire(wye) is used (400/230volt) Japan, on the other hand, uses a full 3 phase distribution system and does not use center tapped transformers to provide high/low voltage to homes - they actually feed 2 phases to each house like many MURBs in North America - so they get nominal 120/208 instead of 120/240. Both 50 and 60 hz are used, and much of the country is 100 volt, instead of 120 - and some is 115. (must be fun if moving from place to place within the country to get the right equipment ----)
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On Mon, 25 Nov 2013 21:44:28 -0500, snipped-for-privacy@snyder.on.ca wrote:

I believe most generators in the use are Delta, where loads, as you state, are Wye. Transimisson is Delta as is most distribution, IIRC.

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On 11/26/2013 1:09 PM, snipped-for-privacy@attt.bizz wrote:

My recollection is transmission is wye at the source and delta at the end (that is transmission line connections to the transformers). This is not something I ever work anywhere near.
Distribution at my house is 13.8kV phase-to-phase and 8kV phase to neutral. I have an 8kV distribution wire (and distribution neutral) running down my alley. I believe most distribution is wye. All the distribution transformers I see have one high voltage insulator, which has to be wye.
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I think you have that backwards. There is no reason to ground reference the source but there is at the substation. It has to be for the next level. Doing it that way reduces Earth currents, too.

Sure, but from the substation the other way, it's likely a delta. Neutrals are expensive and really not needed.
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Most, that I have installed, are Wye. Onsite protection of these units is simpler and more cost effective. 3+ units going straight onto grid as Wye (stepped up, of course) or a Wye-Delta step-up. However, most long range delivery is done via a pure Delta (no neutral) system.
The type of transformer system depends on where on the grid the sub-system is pulling from, and if the utility wants to cooperate with the end-user. In certain situations they will tell you to bugger off since you might be the only service trying to pull a Wye drop in a 90%+ Delta grid. I know of one machine shop that begged for a Wye service to gain 1/3 more 120V branch circuits out of their almost overloaded 1200 amp Delta service. The answer was no, unless they wanted to pay for the entire switch over.
It was cheaper to purchase a Delta-Wye transformer and have a new drop brought in and have all of the 120V circuits transferred over to the 120/ 208 panels. Total PITA to accomplish, but allowed the original service to gain some breaker spaces, equalize the load distribution to all phases, and permitted the installation of a couple more three phase mills and some headroom for that poor, old, tired Delta service. On hot days that thing would be around 1% away from going critical. This was with cooling added to the distribution panel.
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On Tue, 26 Nov 2013 22:35:46 -0600, Nightcrawler®

You install power company generators? Why would protection be simpler?

"Distribution panel"? Are we talking about the same thing?
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I used to install power-plant generators, yes. Not utility generators. These private plants fed the grid and were under the ultimate control of the utility, meaning that the utility could kick them off-line, at will. Most of the plants were not stand-alone. If the grid went down, they went down. The gas-turbine plants were stand-alone, and some city service generation facilities were, also.
Per generator:
A Wye system only has the standard voltage/amperage/frequency/ ground-fault protective systems. Each phase has one bus, two detection transformers (CT and PT), and the neutral is grounded through a current transformer. The neutral does not go out of the plant. The ground fault and generator detection trans- formers are installed on the generator side of the 52G breaker.
The utility only has one set of detection devices in the plant, right after the service entry switch. This set-up provides the best user safety for power generation.
Delta systems are set up primarily the same way with the exception that they usually do not have a grounded leg, hence, no reference to ground. To get a reference to ground requires a complicated and costly system that is separately derived from the direct gener- ation process. These things take up a lot of space. There is no way to have these units inside the control room as with the Wye set- up. Each phase of each generator will have a transformer 1/3 the size of a standard pole pig. This is quite a footprint. My memory of the exact set-up is rather vague, but I do recall a set-up that only sensed the outgoing feed to the step up transformer. That took up a roughly 8' dia. area of ground. I might try to pull up a picture via Google maps.

In industrial/commercial building(s)/complex(s), the service is brought into a distribution panel. This service is 1200 amps and up. The distribution panel feeds other distribution panels directly (building), via meters (complex--separate business'), or a combination of the two. The primary distribution panel uses large form factor circuit breakers that have adjustable magnetic trip settings and are sized, amperage wise, for the load anticipated, either via load calc, or other means. Say, a 400 amp feed to what will be a production facility that uses large machinery and other devices that draw heavy current loads. A 200 amp feed to another section that does not have a purpose at the time of installation and so on until all of the spaces in the dist. panel are used up, or only the immediate (known) service sourcing is to be powered. Why waste the money before the use for the space is known?
(I have to step out for a bit, so I will not be able to finish at this time)
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On Wed, 27 Nov 2013 20:18:17 -0600, Nightcrawler®

That's an entirely different kettle. Of course they're Wye connected because that's what the customer sees. the POWER COMPANY'S generators *are* delta connected, as is the transmission system.

At the customer end, OK, but that has nothing to do with the power company.

Huh? Delta has no neutral.

You're talking about an *entirely* different issue and irrelevant to the discussion.

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On 11/25/2013 1:43 PM, nestork wrote:

As trader noted, the author says "there are four wires coming out of every power plant: the three phases plus a neutral or ground common to all three."
The 4th wire is a neutral, which is grounded.
The author has a problem of identifying neutrals as grounds throughout the piece.
Nowhere does the author describe how earth is used as a conductor in power transmission. ------------------------ "The fourth wire lower on the poles is the ground wire"
The 4th wire is a neutral which is earthed. -------------------------- "Past a typical house runs a set of poles with one phase of power (at 7,200 volts) and a ground wire (although sometimes there will be two or three phases on the pole, depending on where the house is located in the distribution grid)."
The "ground wire" is in fact a neutral wire (which is earthed). -------------------------- "There are two things to notice in this picture: There is a bare wire running down the pole. This is a grounding wire. Every utility pole on the planet has one."
Actually every utility pole does not have one. With the overhead distribution in Minneapolis poles with transformers have an earthing wire. Other poles may or may not have one. --------------------- Continuing "If you examine a pole carefully, you will see that the ground wire running between poles (and often the guy wires) are attached to this direct connection to ground."
The wire is a neutral that is earthed.
The distribution voltage in my area has one of the 3-phase wires tapped off the distribution and feeding 4-8 blocks. The 3-phase neutral is tapped off the supply neutral at the same place and runs with the phase wire. As above, the neutral is earthed at multiple locations. The same primary neutral is used as the secondary neutral, and so the secondary neutral at the transformer is earthed. ------------------------------- Continuing "There are two wires running out of the transformer and three wires running to the house. The two from the transformer are insulated, and the third one is bare. The bare wire is the ground wire."
As about everyone here knows, the 3rd wire is a neutral, not a ground. ------------------------------- There is an electrical diagram of a transformer with the secondary center tap labeled "ground".
Also is obviously a neutral. -------------------------------- There are multiple pictures of distribution lines, all of which have a neutral. Sometimes the author misidentifies the neutral as "ground". Transmission lines also have a neutral. Sometimes it is run on the top for lightning strikes. ---------------------------- "When a 120-volt power line connects directly to ground, its goal in life is to pump as much electricity as possible through the connection."
The electricity does not flow to earth. It returns to the utility transformer through the N-G bond at the service and through the service neutral wire. ------------------------------- The author consistently misidentifies neutral wires as "ground" wires. His pictures show neutrals along with distribution wires. He does not explain how the earth is used in power distribution. He does not appear to understand power distribution.
This piece is fatally flawed.
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On Tuesday, November 26, 2013 11:13:49 AM UTC-5, bud-- wrote:

My hat's off to you Bud. Excellent job taking it apart piece by piece. What's ironic is Danny came in here not knowing the difference between a neutral and ground with a house service. Now he's hitched his wagon to an author that clearly doesn't know the difference between a neutral and a ground either.
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on 27/11/2013, snipped-for-privacy@optonline.net supposed :

Absolutely l-)
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John G



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