Wouldn't the situation where the primary is feed by a single conductor have the same amperage returning through the earth as supplied by the phase conductor? I wouldn't consider that "rather small"
Do you know what the currents are at primary voltages? Your 240V 100A residential service is some 3.3A at the lowest 7,200V primary voltage and something like 680mA at 35kV distribution, and that's only if it's running at the full 100A load which it isn't ever supposed to do for more than a few seconds.
HID Street light ballast igniters are known to produce a lot of RFI when they come on at night, and if they have a bad lamp attached they cycle endlessly producing interference. With the switch to LED street lights and even parking lot lights that problem should gradually become a thing of the past.
On Feb 24, 8:52=A0pm, Metspitzer wrote:
No. Because the primary is supplied from two conductors. In a Multi Grounded Neutral (MGM) distribution system there is a continuous neutral conductor. It is the same neutral conductor that is part of the low lines; that is the lines below the transformer; that supply the individual premise wiring systems. That one conductor is serving as the neutral for both the distribution system and the premises wiring systems served by the transformers that are connected in succession to each phase of the distribution. That uninsulated conductor is grounded at intervals along it's route from the substation transformer were the distribution current originated. In normal operation it carries comparatively little current because of the cancellation that occurs in the common connections. The only current flowing on the neutral is the total difference between the current flowing on the three phases. Not the sum mind you just the difference. So if phase A is carrying one hundred, phase B one hundred five, and phase C one hundred three amperes the maximum current flowing in the neutral conductor at any given instant is five amperes. The actual purpose that the neutral current serves is to provide a larger number of common neutral connections in which the currents from the three phases can cancel each other out. In any portion of a three phase distribution system were all three phases are not present the neutral will carry the same current as the highest current on the one or two phases that are still present. It is only in the three phase portion of the network that the current will cancel out to a very small value. Once that portion of the system ties back into the three phase portion of the network then the current averaged from all such single phased stubs will again cancel out and the neutral current will again be a rather small value.
-- Tom Horne
I got to admit, there is clueless, and there is clueless. This was to the extreme.
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Tom is correct, we have had that sort of a system here in Illinois for at least 50 years.
A electrical engineer friend of mine was once the head of a power company communications division and he told me that many complaints of radio interference his department investigated turned out to be caused by defective doorbell transformers.
TDD
I'm with you on the essence of what you are saying regarding how the power is distributed. Where I still have questions is back to the original observation. Out on country roads, you have 3 high voltage wires, one for each phase. Then you'll have a group of houses. There is a transformer for those houses and it's connected to one phase. Since there are only 3 primary high voltage wires, are you saying the other side of the transformer is connected to the same neutral as the 240V services of the houses? I can see that working, as then you have multiple connections to earth ground for return on the primary side. But then there is also clearly substantial current flowing through earth ground back to the substation or more likely I guess to other earth ground points with other nearby pole transformers that are on different phases.
If it's not done that way, then I don't understand the return path from that pole transformer. All I see are the 3 high voltage wires and then below it the 3
240V service wires, 2 hots, one neutral, going down the road. In other words, there is no neutral return path that I can see other than the 240V, secondary one. So, is it shared? I think that is what Bud said he thought might be going on too. And that seems to be the essence of the OP's question that has him stumped.
Totally irrelevant to what dennis asked.
In the urban area here the primary return is by the continuous secondary neutral, which attaches to the primary neutral at the feed point. It is multi-grounded, but the wire is lower resistance than the earth (or at least lower resistance than the earth connection). In rural areas I don't remember anywhere there wasn't another wire on the pole in addition to 1 or 3 distribution wires. Transmission wires don't necessarily have a neutral because it can be created at a substation. There may be solely earth return somewhere in the state, but I don't remember seeing it.
Sounded pretty crazy the first time I saw you post it.
Jeff Wisnia came up with an FCC interference handbook
Ahhhh-haaaaa!
So that's how they ground the Space Station and other satellites!
I have been on a lot of country roads and have never seen what you described. Typically there are the Y derived phase conductors on a crossarm or bracket with three insulators and an uninsulated neutral below. As density gets lower they will only carry one of the primary conductors and the neutral.
They are both.
The pretty much standard system is a Y derived HV primary ~ 12kv phase to phase or ~ 7.2kv phase to neutral.
I had two houses but never heard of that. Perhaps I did and forgot. Years ago our ham club had an interference expert from PG&E, come in to our meeting. The way he tracked down that type of interference was use am radios. You start at the broadcast band then work your way up in frequency, narrowing down the location. Like, am broadcast, cb, aircraft band, etc.
The transformers I see know have a thermal break, for good.
Greg
The one here appears to have the neutral on top. See the picture at
Metspitzer wrote in news: snipped-for-privacy@4ax.com:
talking to the utility guy replacing the power transformer on the ground outside my apartment(after it blew),it was fed by 7200 volts,coming from a nearby pole.
The theory with that is the neutral up top is most likely to take a lightning strike. They do the same on the long haul transmission lines.
I've used pocket sized AM radios for years to find powered Romex inside walls before making any cuts into plaster or Sheetrock. ^_^
TDD
Another common high voltage power feed in the U.S. is 13,800 volts.
TDD
Oh, this is cheap and great for finding near field electrostatic noise, and
60 power lines. Using the transmitter, unpowered wires.HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.