Pole xformer connections

[quogueelectric]

I think it is in kva

I think it is in kva

How do you interpet the markings/size of the can? Along the same lines, how many residences are one can? Or does that depend??

The one I am using at work says 37.5 I would guess that that is the kva rating on the can. Probably service 5 or 6 homes however this is just a guess on my part. What I di find out today was the answer to my question which ties into and opens up a lot of worm cans on this site as far as the grounding positions . I emailed a long time friend about where the other side of the primary winding was connected and he is a longtime lineman for the local power company. This was his response ( "every transformer has a primary nuturel/ground that goes to ground but not every pole.Only tranformer/switch poles have down grounds.And poles that have lighting aresters/high voltage equipment.The down grounds are #6 cu and a 8ft ground rod. I hope this helps." ) so current does flow to ground on a regular basis contrary to the anti grounding group on this site. as far as how many houses you can put on the xformer when I hooked up a 2400 amp temp servce to a large rudd xformer 1 13.2kva loadbreak to supply it I said to the power co guy this xformer is way overloaded he told me dont worry about it let me worry about it so I said you got it it never did blow up in 8 yrs or service

 

[mdshunk]

so current does flow to ground on a regular basis contrary to the anti grounding group on this site.

Of course some does. Kirchoff's law. The pole butt ground is not the "neutral" of the primary, however.

Your friend must work for an odd utility, because most modern utilities have a pole ground at each and every span.

 

[quogueelectric]

primary winding return

primary winding return

Of course some does. Kirchoff's law. The pole butt ground is not the "neutral" of the primary, however.

Your friend must work for an odd utility, because most modern utilities have a pole ground at each and every span.

If you connect 3 alternate primary phases they will circulate between commonly bonded cans however the primary current for a single pot out in the woods is about a 50=1 ratio so a house on its own line with a 200a draw will be returning 4 amps of primary current into the ground at 13.2 kv. as long as everyones grounds are attatched propperly this all works safely. What I am pointing out ad nauseum is this IS the return to the source aka the neutral. My friend did say that there is a downground at every xformer and equipment which would include the multigrounded neutral span.

 

[mdshunk]

If you connect 3 alternate primary phases they will circulate between commonly bonded cans however the primary current for a single pot out in the woods is about a 50=1 ratio so a house on its own line with a 200a draw will be returning 4 amps of primary current into the ground at 13.2 kv. as long as everyones grounds are attatched propperly this all works safely. What I am pointing out ad nauseum is this IS the return to the source aka the neutral.

What are you calling "grounds".

I just hope you aren't talking about the earth (soil). That's what I'm trying to make sure of. There is actual wire involved here.

 

[quogueelectric]

negative

negative

What are you calling "grounds".

I just hope you aren't talking about the earth (soil). That's what I'm trying to make sure of. There is actual wire involved here.

What I am saying is groundrods to the earth one at the pole one or 2 at the house in the most simple application A #6 solid copper just like the lineman said. He called it a neutral/downground I also think that it makes it an unatractive lightning target being connected to so many groundrods in a heavily populated area with more houses and more services all grounded commonly. Just to be perfectly clear I am talking about electron flow across your lawn if the substation is behind your house or annother downground on a different phase. nearby

 

[LarryFine]

What I believe Marc is saying, and I agree with him, is that the earth is not the sole return for the primary syatem. Every distribution transformer I have seen is supplied by a primary conductor that has a system neutral/grounded conductor run with it.

I have never seen a primary conduuctor run without a corresponding grounded conductor. Ever. Will they function without one? Probably, and probably well enough for a break to go unnoticed for a while. But done so by design? Not that I've ever heard of.

Added: One of my best friends is a transmission/distribution engineer. I'll try to remember to ask him about this tomorrow.

 

[don_resqcapt19]

quoqueelecgtric,
There is a "return" conductor on almost all primary distribution in the US. Single Wire Earth Return (SWER) is very rare here. In our distribution the primary and secondary grounded conductor is often the same conductor. That being said, the multigrounded neutral system does place the earth in parallel with the utility grounded conductor and there will be some grounded conductor current flowing in the earth. This current is often the source of "stray voltage" at dairy farms and pools.

so current does flow to ground on a regular basis contrary to the anti grounding group on this site

As far as current flowing to ground, that does not happen .... current only flow back to its source...the ground or earth may be a conductor for some of that current.
Don

 

[LawnGuyLandSparky]

I'll say it's safe :grin: [as long as you don't mean earth ground, but rather the grounded condcutor]

Here's a pic I took of a pot across the street from my house:

Wow you got your own darn dedicated transformer!

 

[LawnGuyLandSparky]

How do you interpet the markings/size of the can? Along the same lines, how many residences are one can? Or does that depend??

In NYC's underground Con Edison secondary distribution, as many as they can until it blows up.

 

[wptski]

On my street there's a can on every fourth pole which is between two streets which puts four homes between each pole. The pole with can in my backyard was replaced a few years ago. I know that my sevice comes from that one but I've wondered how far its service goes.:-? I didn't care at that time to ask.

Just looked! Mine is marked 50 and the word DUAL. It feeds the home behind me, next to me and the one behind of that one bacause I can see the connections. Sketching the layout on paper, I guessing that it's twelve homes on each can.

 

[72.5kv]

Typically, a 25KVA or 37.5KVA will handle 3 or 4 homes; 50KVA 6 to 8 homes; 75KVA 10 to 12

When my mentor at an electric utility showed me the typical demand value for a home, it was usually about 30 percent of the service size. Beside he told me its not uncommon to overload them by atleast 200 percent sometime.
they had a yard full of these transformers.

The only transformers this utility really care most for where the one at the distribution substation typical sizes were 30MVA and at the transmission station 150MVA and larger. These are not off the shelf transformers. all costume made. 6 month to a year wait time.

 

[peter d]

In my neighborhood, it's like taking a walk down POCO memory lane. Ancient transformers, cutouts, and OH lines and service drops that are copper instead of aluminum. A large amount of the system hasn't been updated in a long time, except for hurricane damage repair. And since National Grid is the poco, I highly doubt they will be updating anything unless they absolutely have to.

Why do those transformers use an insulating bushing for the "neutral?" Is that necessary?

 

[LarryFine]

Why do those transformers use an insulating bushing for the "neutral?" Is that necessary?

If it's a small bushing, it's just a pass-through. If it's a large bushing, hi-voltage rated, it's because the transformer can be used either line-line or line-neutral.

 

[loren]

What a lively discussion.
I refer to single bushing transformers as Stray Voltage Generators.
Yes all systems that I have seen have a grounded wire that comes along with the high voltage hot lead.
Yes in some states every pole has a ground on it.
No in 99.9% of the time the earth does not carry all the neutral current but the connection between ground and the neutral/grounded high voltage wire being attached to the ground creates a voltage divider circuit. The path with the least resistance carries the most current. I recently worked with a farmer that had a stray voltage issue. The #4 neutral utility conductor was 11 miles long. Do the math, if the wire had no splices what would the resistance be? Now in this farmers case there was a stream behind his farm that ran to with-in one mile of the substation.
From half way up that line to the farm which was at the end of the line current traveled to him on the neutral and them into the ground through the farm and into the creek.
I was not there (and against counsel) for this but it I was told to me that when a double bladed axe eliminated the grounds from the four poles that were parallel with his farm the problem was solved.
In case you are wondering his farm is completely three phase the only completely three phase load on that feeder.

 

[mdshunk]

I was not there (and against counsel) for this but it I was told to me that when a double bladed axe eliminated the grounds from the four poles that were parallel with his farm the problem was solved.

Ah... the Paul Bunyan stray voltage elimination technique. :grin:

 

[peter d]

So the solution to stray voltage would be to use line-line transformers instead?

Electrically, it makes sense to me. But you would still have to ground the secondary, wouldn't you? That would still create a path back to the source, would it not? (Albeit a much longer one to the nearest substation, generating facility, etc)

 

[mdshunk]

But you would still have to ground the secondary, wouldn't you? That would still create a path back to the source, would it not?

Yeah, I'm not sure I agree with him on that one. Use a two bushing pot for single phase, and you're still going to put in enough jumpers to make it just like a one bushing pot anyhow.

The only thing I've seen to address current flowing on the pole grounds is the Ronk blocker. Ronk is the same company that makes about 95% of the pole top generator transfer switches used on farm poles. There's a few of these Ronk blockers used on dairy farms in my area. You wire it between the primary and secondary neutral connections. I'm not sure what sort of hocus-pocus is inside the box, but they work.

http://www.ronkelectrical.com/pages/otherproducts.html

 

[loren]

The only real answer is to use a five wire system. Never allow a neutral that is not double sized (to handle the increasing amount of harmonics) and a ground.
Harmonics can not balance them selves out within even a three phase system. This current must travel back through the neutral.
Todays system with the much smaller neutrals build up such high neutral to ground voltage that more and more current is being forced to travel back through the ground.
(not to insult) current through resistance creates a voltage.

Something to ponder; If your pentium 4 processer runs on 1.8 volts and the neutral to ground voltage at the outlet is above that, is it any wonder why people see the blue screen of death on there computers more and more. How can the processor pass the interference off to ground?
Food for thought

 

[don_resqcapt19]

The #4 neutral utility conductor was 11 miles long.

And under the NESC that neutral was grounded at least 4 time a mile.

 

[don_resqcapt19]

loren

The only real answer is to use a five wire system.

That would have to be on the primary side...most stray voltage if from the voltage drop on the grounded conductor primary. The primary grounded conductor is bonded to the secondary grounded conductor and this energizes everything that is connected to the electrical grounding system by the amount of the primary voltage drop when measured to remote earth.

Something to ponder; If your pentium 4 processer runs on 1.8 volts and the neutral to ground voltage at the outlet is above that, is it any wonder why people see the blue screen of death on there computers more and more. How can the processor pass the interference off to ground?

It never sees that voltage...the secondary side of the computer power supply is not a grounded system. The blue screen is only because the people in Redmond. WA don't know how to write software that works.
Don