Closed Delta 120/240V 3-phase service

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
Reply to
VWWall
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| snipped-for-privacy@ipal.net writes: | |>| |>| |>| I would assume no effect, as long as the insulation was rated for 208VAC |>| to ground vs. 120VAC to ground, and you don't overload the possibly small |>| high leg transformer. The insulation won't be an issue for anything |>| designed for European use where either leg may be hot, since either leg |>| must handle 240V. One overload problem is when something is connected |>| across the missing leg of an open delta system. The transformers have to |>| deal with a higher VA per delivered watt, plus more copper losses. |>| Combine this with a small high leg transformer and you may see voltage |>| sag. | |>Would a computer overload it? | | What do you mean by "computer"? A PC or a big-assed old mainframe? | I seriously doubt a PC with a 400W power supply will overload a high leg | transformer of a few kVA.
PC. I didn't think so.
The old mainframe might want three phase (to run its 400 Hz motor-gen set).
Reply to
phil-news-nospam
I did see, many years ago, something close to this. We called it a 'phase-shifting' transformer. IIRC, three of the outputs went to a delta-delta isolation bank and the other three went to a second delta-delta. Each delta-delta isolation bank fed a three-phase rectifier and the two rectifier outputs were combined. Used it to provide a lot of rectified DC.
The phase-shifting transformer's two outputs where shifted 15 degrees and with the isolation transformers greatly reduced the odd harmonics (third, fifth, and seventh) which was a big issue since it was a shipboard installation and the supply was far from 'infinite bus'.
Don't remember exact connections anymore though, that particular 'BeeBee' has fallen out and been replaced by other trivia :-)
daestrom
Reply to
daestrom
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.
Reply to
Michael A. Terrell
...and how does this "six phase" differ from a center-tapped three- phase?
Three phase delta?
No need for six-phase transmission to get six phases at the "apartment building". Like you, I don't see the point though.
Dunno, I'm not a power jock...
Reply to
krw
If I remember correctly, both transformers had 1 MV bushing, connected to different phases, and the secondary was wired as open delta.
There are maybe two places near here where there are 2 transformers of equal (physical) size that I think are wired as open delta. I'll take a closer look, just in case.
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.
4 on the big can, I believe 4 on the small can.
There are a fair number around here (central Mass.), maybe 5-10% of all pole installations. Want photos? :-)
Any photography will have to wait several months before I go to the Philly area again. I have a single photo of one setup which doesn't help figuring out what's going on since the LV wiring is all bundled up.
Reply to
Michael Moroney
I've heard that many single unit 3 phase transformers are internally wired as Scott-T, since this requires only two cores and two sets of windings instead 3 cores/3 sets of windings. Both the primary and secondary are wired in the configuration of the 3 phase side of a true Scott-T configuration.
Reply to
Michael Moroney
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.
Reply to
VWWall
I spent 20 years working in HF broadcast for the BBC external services, then 7 years "domestic" - LF, MF, VHF and UHF TV then the last 10 years repairing Microwave link equipment. I retired April 2007.
Can't say I've heard of that one, however, checking a definition via google I think we would just have referred to "an internal flash-over" - not something that happened very often. Seemed more common in Vac capacitors which, without the protective circuits that valves usually had could sustain an internal arc for several seconds.
Take a look here:
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I was never at Wofferton, spending all my HF career at Daventry but we had the Marconi BD272s shown here in the first four pictures. The BY1144s were used as final and modulator valves and had the two-phase filament we were talking about. They were vapour (steam) cooled using the "steam down" arrangement. By the look of the pictures Wofferton didn't take as much care of their transmitters as we did!
(Note the safety "earthing wand" in some of the pictures)
When he speaks of needing 15mins for a wavechange however he is somewhat exaggerating - two people working as a team would take around 5mins to change all the coils and put all the settings on prior to powering and tuning. (Welding gautlets were used to handle the hot coil members)
The last picture, of Sender 83, was like the new transmitters installed at Daventry before I left. The Wofferton ones had a sort of pre-set tuning arrangement and operated by remote command from a computer system that ran the schedule. The Daventry ones (300kW) were a little later and fully auto-tuning over the entire band.
The frequency synthesizer providing the drive was commanded via its HPIB bus from the station computer control system. The Tx had what amounted to a frequency counter at it's input, which derived the address for some EPROMS, which stored coarse tune settings. Pneumatically operated switches operated to tap the tuning coils and stepper motors wound Vac caps to the correct place (HT was suppressed during this operation). Phase discriminators provided fine tune information once low HT had been applied.
They had very fast acting protection for the valves (tubes) to prevent internal damage.
It was tested by hanging about 5 feet of 5A fusewire from the HT (11kV) supply to a vacuum contactor. The contactor was closed putting a dead short across it and the protection was fast enough to prevent the fusewire from blowing. It was quite spectacular when it didn't :-)
Reply to
Stuart
As an aside, I should have mentioned that the BD272s used two transformers to give a six phase supply (since that seems to be the topic under discussion) to two banks of six AR64 Mercury arc rectifiers.
Reply to
Stuart
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
Reply to
Beachcomber
| |> |> >> B C |> >> \ / |> >> \ / |> >>A----N----D |> >> / \ |> >> / \ |> >> F E |> > |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound |> >>on the second core. C-N and N-F are both wound on the third core. A third |> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240 |> >>loads would be served from B-N-E. A third of the 120/240 loads would be |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N. |> > |> >I always wondered if either any electric company offered such a service, |> >or if there was any such thing as a breaker panel that would support it. |> |> Are we not forgetting about the primary windings for such a scheme? | | ...and how does this "six phase" differ from a center-tapped three- | phase?
When most or all of the loads are single phase, the "6 star" can keep the loading balanced over the 3 incoming phases, while also providing genuine 240 volts to those single phase loads. 240DCT or 240DVCT puts most of the loading on one phase angle (which might be 2 incoming phase lines). 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich on the L-N circuits. 220Y/127 is sometimes a compromise.
|> Also, doesn't six phase distribution mean six phase transmission? Six |> phase transmission for any distance is going to be horrorendously |> expensive just to keep a few apartment buildings at 120/240 V. | | No need for six-phase transmission to get six phases at the | "apartment building". Like you, I don't see the point though.
Which would you be willing to give up? Having 240 volts (and instead you settle for a wimpy 208 volts) or having the phases balanced (this is more of a utility concern)?
Reply to
phil-news-nospam
|>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.
Reply to
phil-news-nospam
|> |> |>> A Scott-T is used to get two phase from three phase. There are very few |>> two phase requirements any more. |> |> 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. | | 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.
You could run that from your three phase power if you wire things up to get the right phase angles AND the right voltages. If a motor is wound so one phase is 240 and the other is 208, that should be happy on either 240DCT or Scott-T. But such a motor would not be run very easily on a Wye system without some additional winding tricks, and that would negate any economics of 2 windings.
Reply to
phil-news-nospam
A tested out of the three year broadcast engineer course at Ft. Monmoth in 1972. I got the highest score on record at Ft. Knox, KY for my M.O.S. My final duty station was an AFRTS radio & TV station at Ft. Greely, AK.
I didn't get back into broadcast until the late '80s, when the station was responsible to the FCC. Most of my work was consulting on older equipment the young punks couldn't fix. I did move and rebuild a RCA TTU-25B UHF TV transmitter for a station in Destin Florida around 1990. Had lots of fun with the building inspector who had no idea what I was doing. His last words were, I'm getting a cease & desist order!!!... when I asked him what he knew about 10 KV armored HV wire.
I am 100% disabled these days, and no longer doing broadcast work. I miss it, but no one will hire someone with all my health problems. :(
Reply to
Michael A. Terrell
Maybe I'm dense, but I see *no* difference between the two schemes. ELectrically, I don't see how you could tell one from the other.
Before I can tell you my preference in donuts, I need to see the difference between six and half a dozen. ;-)
Reply to
krw
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.
Reply to
krw
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.
Reply to
Michael A. Terrell
A six phase rectifier reduces the AC current through the filter caps, as well as the total capacitance needed to achieve the desired ripple voltage. The lower the AC current, the less chance of a capacitor trying to go into LEO.
Reply to
Michael A. Terrell
A second could work under a first, who took responsibility.
Reply to
Michael A. Terrell

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