Closed Delta 120/240V 3-phase service

On Fri, 15 Feb 2008 00:19:59 +0000 (UTC) Michael Moroney
|>If the big can is already 3 phase, why would anyone need to also have a
|>Scott-T? That doesn't make sense. It must be something else. How many |>MV bushings on each can? | | 3 on the big can, 0 (yes, zero) on the small can. | | I called it Scott-T like because I'm guessing the small can is fed from | the 240 delta high leg to neutral, which would be 90 degrees shifted from | the 240VCT winding. Assuming my guess at what it is is correct at all. | |> How many secondary lugs? | | 4 on the big can, I believe 4 on the small can.
So the small can had 4 lugs and no MV bushings? Sounds like it might be wired in as some kind of autotransformer. Maybe it is correcting the voltage on the high leg or something.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) writes:

I looked at my photo again, and it is understandable what is going on after all. See for yourself:
http://www.accvio.com/temp/two_cans.jpg
http://www.accvio.com/temp/two_cans_large.jpg (full size)
It's not clear the large transformer has 3 MV bushings, but it does.
One connection from the large transformer goes only to the small one, 3 others (1 connected to a bare neutral) go below it and two additional leads from the small can go downward, for a total of 5 leads that run down the pole.
There's another (probably) 120/240V service going left to right (with a drop to the upper right) that's appears not to be involved or connected, except for the neutral.
It appears to me, if the large can is delta with the lead to the small can the high leg, that this is a 5 wire 2 phase circuit, or what many would call 4 phase, 4 poles spaced at 90 degrees and a neutral. Can anyone suggest an alternate possibility?
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On Fri, 15 Feb 2008 21:16:12 +0000 (UTC) Michael Moroney
| snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) writes: |
| |>>On Thu, 14 Feb 2008 20:15:45 +0000 (UTC) Michael Moroney
| |>>| One weird setup I've seen, and I'm not totally sure exactly what it is: |>>| 1 large 3 phase transformer (single can) with a small transformer can |>>| below it on a pole. The small transformer has NO MV connection nor even a |>>| MV bushing! It sits below the drops to the homes/businesses. The only |>>| thing I can think it could be is the big can is 240V delta, and the high |>>| leg powers the small can, with is a 208V/240VCT. The big can powers half |>>| the residential services plus any 3 phase services, the small can powers |>>| the other residential services. It's sort of Scott-T relative to the big |>>| can. But this is a guess, I actually don't know how it's wired. I even |>>| took a photo to try and figure it out. There are quite a few of these |>>| setups in Philadelphia. | |>>If the big can is already 3 phase, why would anyone need to also have a |>>Scott-T? That doesn't make sense. It must be something else. How many |>>MV bushings on each can? | |>3 on the big can, 0 (yes, zero) on the small can. | |>I called it Scott-T like because I'm guessing the small can is fed from |>the 240 delta high leg to neutral, which would be 90 degrees shifted from |>the 240VCT winding. Assuming my guess at what it is is correct at all. | |>> How many secondary lugs? | |>4 on the big can, I believe 4 on the small can. | | I looked at my photo again, and it is understandable what is going on | after all. See for yourself: | |
http://www.accvio.com/temp/two_cans.jpg
|
http://www.accvio.com/temp/two_cans_large.jpg (full size) | | It's not clear the large transformer has 3 MV bushings, but it does. | | One connection from the large transformer goes only to the small one, 3 | others (1 connected to a bare neutral) go below it and two additional | leads from the small can go downward, for a total of 5 leads that run down | the pole. | | There's another (probably) 120/240V service going left to right (with a | drop to the upper right) that's appears not to be involved or connected, | except for the neutral. | | It appears to me, if the large can is delta with the lead to the small can | the high leg, that this is a 5 wire 2 phase circuit, or what many would | call 4 phase, 4 poles spaced at 90 degrees and a neutral. Can anyone | suggest an alternate possibility?
It looks to me like what is going on is that the first can provides common 208Y/120 like:
B / / A-----N \ \ C
And then the second can turns one of the phases into 120/240 like:
B / / A-----N-----A' \ \ C
Most of the loading is 3 phase where 208Y/120 serves the need, but some load needs genuine 240 or split phase 120/240 and they didn't want to hang a 2nd can up high to do it directly from MV (and can't bring the MV down to where the 2nd can is now).
Just a guess.
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snipped-for-privacy@ipal.net writes:

Except, there is no connection to one lug of the big can except to the small can, so you get either:
B / / N-----A' \ \ C
or maybe
B / / A-N \ \ C
(trying to show a different voltage on A)
or some combination. Not too useful IMO.
There are quite a few of those things in inner city Philly, as well as some other odd practices.
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On Sat, 16 Feb 2008 05:00:07 +0000 (UTC) Michael Moroney
| Except, there is no connection to one lug of the big can except to | the small can, so you get either: | | B | / | / | N-----A' | \ | \ | C | | or maybe | | B | / | / | A-N | \ | \ | C | | (trying to show a different voltage on A) | | or some combination. Not too useful IMO. | | There are quite a few of those things in inner city Philly, as well as | some other odd practices.
Curious-er and curious-er. It might need an investigation.
I wonder if maybe there might be a Scott-T inside that big can and the little can could be modifying it somehow.
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snipped-for-privacy@ipal.net wrote:

A Scott-T is used to get two phase from three phase. There are very few two phase requirements any more.
Some erroneously call the 240/120V system "two phase" when it's really a single phase with a center tap. (Or two 120V windings connected in series.)
The last time I encountered a true Scott-T was in my exam for Professional Engineer, back in 1952.
--
Virg Wall, P.E.

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Often used for the filament supplies in the modulator valves on large AM transmitters. Two seperate filaments fed from the two different phases to reduce hum caused by modulation of the anode current due to variation of the emmision at mains frequency.
--
Stuart Winsor

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Stuart wrote:

Yep. That's one of the very few. I worked as a "broadcast engineer" whilst going to college. I still have my Radio Telephone First Class license.
There used to be a few two phase motors, but they're almost extinct.
Since you know about high power valves, do you remember the Rocky Point effect?
Virg Wall, P.E., K6EVE
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VWWall wrote:

Sure you do. There have been no new, or renewals of the 'First Class Radio Telephone License' for over 20 years. It was replaced with the 'General Radio Telephone License'. It was long gone when I went back to broadcast engineering in '87.
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Michael A. Terrell wrote:

I first got it and my Telegraph Second in 1946, when I was discharged from the Army Signal Corps.

I forgot to say that is has the words "CANCELED" stamped on the last renewal certificate, (P1-11-49835 Sep 23, 1976), which was a handsome looking document. As you say it was replaced by the General license, the only evidence for which is a little pocket card.
My last renewal of my Second Class Radiotelegraph License was Oct 15, 1981. After that they started charging for renewals.
Did you get your FCC Registration Number, which you now need do business with the FCC? It gives you a password which must be used on their site.
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So that must mean that you know how to "Dip the plate and peak the grid"...
The way it was...
I remember those days well. It was around 19 74 or 75 when I went down to the Chicago Federal Building FCC offices. There was a big classroom where they gave the tests. The tests were all multiple choice and had a lot of trick questions.
If you were really a hot operator, you could also take the test for Element 9 which was the "Radar Endorsement". That meant that you were better than the guy who had a mere First Class Radio-Telephone License without it. A lot of military and maritime guys would take the First Class Radio-Telegraph License Test which was really cool, as well.
In later years, the FCC test stimulated the startup of a lot of instant hack schools where they gave you the answers to actual FCC tests. Anybody who could memorize the answers would get a "ticket".
Back then, even the disk jockeys needed at least a Third Class Radio Telephone License if they were going to operate a low-to mid-power radio station's transmitter.
Operation of a transmitter at a higher power station required the First Class License.
If you got your license from going to such a school, you were often considered a lowly "nine-week" wonder or whatever the length of the school was by the people who had done it on their own.
There was a lot of pressure during those times to bring more women and minorities into broadcasting and the broadcast station owners, among others, lobbied to do away with the tests.
Before this, the government was limiting the supply of qualified broadcast employees by requiring high standards and testing before granting you your "ticket". From an employee standpoint, this was good because the low supply kept wages high.
Beachcomber
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says...

Commercial transmitter operation also required a "transmitter endorsement", IIRC. I don't remember the details, but I had one in the early '70s (took the tests in Chicago).

Didn't think a first class was needed for radio, only TV.

Artificial limitations never work for long. Unions have had their day too.
--
Keith

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krw wrote:

A second could work under a first, who took responsibility.

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snipped-for-privacy@earthlink.net says...

Sure. I meant as the primary transmitter operator. A first-class wasn't necessary 24/7. The guy that maintained the indian didn't need a first. ;-)
<snip>

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krw wrote:

WPFB. the local AM & FM station in Middletown, Ohio had several engineers with a first class ticket. The AM was a daytimer, and later, allowed low power nighttime operation. They ran a background music service they called Musiplex as a SCA service. In the early days there were no commercial SCA equipment, so they built tuners & receivers and leased them, with their music service. One of the engineers must have been in love with Nuvistors. There was about a dozen nuvistors, and each section was built on a steel plate that mounted between a coupe sets of rails. The RF sections looked odd enough, but the 20 W PA amp look really funny.
http://en.wikipedia.org/wiki/WPFB_ (AM) http://en.wikipedia.org/wiki/WPFB-FM <http://www.middletownlibrary.org:8080/cgi-bin/viewer.exe?CISOROOT=/Crout&CISOPTR )52&CISORESTMP=&CISOVIEWTMP=>
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Beachcomber wrote:

I remember the sample tests. They remind me of "Who Wants To Be A Millionaire" with their stupid choices.

I did some RADAR work in the service. Some of their techs were on leave, and others were sick so they called my section to borrow a tech. The guy got pissed when I told him I had studied RADAR on my own, in high school, and was even more pissed before the day was over because I could take a few readings and locate the problem before he could carry in all of his toolboxes and spare parts. By the time I got back to my section they were already trying to have me transferred to the RADAR section. The only thing that saved me was that orders were already cut for Alaska.

At one time you were supposed to be able to present your DD-214 to the FCC with my M.O.S. on it, and get the first class ticket without taking the test but that policy changed while I was still on active duty. That was why I said forget it, and went into servicing industrial electronics.

And some had a very hard time passing that simple test. :(

You can imagine how I was treated in the Army when they learned it was a 'civilian awarded skill' and didn't spend three years at Ft. Monmoth. :(

After that, the wages were insults. Ch 45 in Dayton ohio was looking for a chief engineer. They were offering minimum wage for a 40 hour a week salary, and expected you to be available 24/7. I laughed in their face and walked out the door.
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snipped-for-privacy@earthlink.net says...

I remember one, to this day;
As the licensed transmitter operator, if the antenna lights fail, do you:
A) Climb the tower and replace the light bulb B) Cut down the tower C) Dismantle the transmitter D) Call the FAA and advise them of the danger
My choice at the time was E) laugh my ass off.
--
Keith

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krw wrote:

Of course, the answer is D). That is why tower light monitors are required.
What is real fun is when you move to a different tower, and still have to monitor the lights at the old transmitter site. I had to do that at WACX. I used a 1.024 MHz crystal and divided it by 1024, then filtered it to get a fairly clean sine wave. A current transformer monitored the circuit. The sine wave was on, when there was at least one light out. That way, when the beacons flashed, the signal dropped for a second.
At the other end, I used a 567 tone decoder to detect the 1 KHz signal. There was a small, but bright LED in the mater operator's field of view. They logged when it started flashing, and when it stopped. If the light went out it meant there was no AC at the old site, and that was logged in and out, as well.
BTW: My choice would have been F). Find the idiot who wrote the test and make them re-write it so that all questions were closer to the proper answer. There should be no throw away questions on a test like that.
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Michael A. Terrell wrote:

I took the exams for First Phone, Second Telegraph and Amateur, in New York City, shortly after I was discharged fron the Army in 1946.
The FCC exam proctor noticed I was doing well on the first couple of elements I handed in and told me to do just about 80% and turn them in. If I didn't get the required 70% to pass, he'd give them back for me to try a few more questions. Of course I'd pick the easy question to answer first.
He said I had the record for most elements passed in one day. Probably also the record for the lowest passing score!
--
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snipped-for-privacy@earthlink.net says...

I "worked" at WPGU-FM (at the time the only network affiliated student station) for a while. Their transmitter was on a 12-story dorm building about a mile from the studios (in the basement of another dorm building). THe logs were taken remotely over a phone line with a contraption that consisted of a rotary phone dial and meter. One of dial "positions" ('9', IIRC) returned the antenna light current, which was logged every half hour along with all the rest of the stuff.

As far as I was concerned, the whole test was throw away questions like that. It was a waste of a day and a trip to Chicago.
--
Keith

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