wye delta 480 with a grounded leg

[Pootnaigle]

The utility I worked for discontinued 480 delta 3 phase service on any new construction. I spoze it had to do with the use of higher distribution voltages and ferroresonance. My question is couldnt you use 3 -277 pots, float the seconday neutral and ground one leg of the hots? The phase to phase voltage would be 480,just like the 480 delta only it would be wye-wye, Instead of wye delta.Prolly wouldnt phase with an old installation but seems to me it would work just fine once you rotated it and cut it over. spoze it would only pose a prollem if you only had 2 phases of primary available tho.

[ratbastard101]

From what I have learned about the 480 power delta bank......you could replace it with a 277/480 Wye/Wye bank if all it is feeding is motor load. This is due to the windings on the motor being rated only for phase to phase voltage and the phase to phase voltage is the same on either bank. We also do not build the power delta bank for new construction and only have 2 or 3 even left in our system. In doing this you would build the Wye/Wye bank the same way you always would and ensure that all grounds have been removed from the phase that was grounded for the Wye/Delta power bank on both the utility side of the service as well as on the customers side. Since the equipment only needs phase to phase voltage there would be no need for a neutral or common but only for an equipment ground.

[Boomer gone soft]

I think ratbastard is correct.

Even without the grounding issue, the two would be 30 degrees apart and not phase.

[Trojan]

That's right. 30 degrees out of phase. We install new 480V with a wye secondary. Some customer do not want any relationship to earth, so the 3 sec'y neutrals are connected to each other but not connected to system neutral or earth. Older customers may not have agrounded service, those transformed sec'y neutrals are connected to system but nothing to customer.
Code now requires 480V to be grounded, neutral in service connected to system. Been that way around here for about 15 years. Older 480V used to ground B phase to earth with #6 copper. Problem if a 480V phase became grounded. Sometimes a fuse would blow but if it was large fuse the #6 would burn off first. Then there be equipment that should be grounded alive between 0V and 480V. Transformer just sees load and keeps pushing current. It is a flash waiting to happen.
There are still a lot of intrigued 480V transformers in older industrial areas. Get calls from electricians working inside and thinking they have a dead phase because they are measuring to ground. Or they have step down dry types for lighting that are 277V primary. Or old factory fed off that dry type and now they have a lot of computers and there is no neutral return path. Makes the screens all jittery.
They are a lot of single phase 480V with no neutral feeding highway lights.
And, now that I'm rambling, 3 phase 480V transformer were 3 bushings sec'y. You can get 3 phase ungrounded 240V delta by connecting to the center bushings.

[dogman]

We had 30 oil field locations, we did this to. Didn't have to change meter, meter loop, sec. wire out. Company saved a little bit of money. Bob

[Trojan]

I s'pose you could take a 7200v-277v transformer and connect the primary phase to phase 12,400v to get 480v on sec'y bushings. Then connect sec'y delta to get 480v delta ungronded. Insulation would have to be rated for higher voltage. It won't parallel with wye-delta 480v though.

[rcdallas]

You can build a Wye-Wye 480 grounded leg bank 3 phase 3 wire. You'd float your neutral on the secondary and ground one of the hot legs.

Get your rotation right and your good to go the way I understand it.

The sole purpose is for phase to phase voltage only...same as a corner grounded delta.

As far as paralleling goes...Wye-Delta or Delta-Wye have 30 degree displacement, Wye-Wye can not be phased with a Delta-Wye...Delta Delta will never phase with a Wye-Delta.

[wtdoor67]

I s'pose you could take a 7200v-277v transformer and connect the primary phase to phase 12,400v to get 480v on sec'y bushings. Then connect sec'y delta to get 480v delta ungronded. Insulation would have to be rated for higher voltage. It won't parallel with wye-delta 480v though.
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You can't take a transformer with 7200 turns on the primary and hook it to 12470 phase to phase. Actually you probably can, I think most have that high insulation value. However the result would be 1.73 times whatever the secondary windings are. If a pot says 12470/ 7200 on the label, then it has 7200 turns on the primary and if it say 7200/12470, it also has 7200 turns. The former is just a single bushing and the latter a double bushing.

If you hook a pot phase to phase it has to have approx. the same amount of turns as the phase to phase primary voltage. Phase to phase on 12470 voltage usually use about 12000/20800 pots. It doesn't have to be the exact but just close to get the desired secondary.

[Boomer gone soft]

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You can't take a transformer with 7200 turns on the primary and hook it to 12470 phase to phase. Actually you probably can, I think most have that high insulation value. However the result would be 1.73 times whatever the secondary windings are. If a pot says 12470/ 7200 on the label, then it has 7200 turns on the primary and if it say 7200/12470, it also has 7200 turns. The former is just a single bushing and the latter a double bushing.

If you hook a pot phase to phase it has to have approx. the same amount of turns as the phase to phase primary voltage. Phase to phase on 12470 voltage usually use about 12000/20800 pots. It doesn't have to be the exact but just close to get the desired secondary.

I think you are right, Danny. You would have to feed a 7200 pot 14400 to get 480 out of an 120/240 secondary. In the case Trojan was musing about, you would get 416.

btw, I don't think the pot literally has 7200 turns....it just has a ratio of 30:1 turns with the secondary winding.

2 bushing transformers don't care if they get their voltage from phase to neutral or phase to phase; as long as the voltage in is its rated voltage.

[rcdallas]

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You can't take a transformer with 7200 turns on the primary and hook it to 12470 phase to phase. Actually you probably can, I think most have that high insulation value. However the result would be 1.73 times whatever the secondary windings are. If a pot says 12470/ 7200 on the label, then it has 7200 turns on the primary and if it say 7200/12470, it also has 7200 turns. The former is just a single bushing and the latter a double bushing.

If you hook a pot phase to phase it has to have approx. the same amount of turns as the phase to phase primary voltage. Phase to phase on 12470 voltage usually use about 12000/20800 pots. It doesn't have to be the exact but just close to get the desired secondary.

I think I've told ya that here we utilize two different system voltages...7200/12470 and 12470/21600.

We have some delta high side banks on 7200 using the 12470/21600 pots. No taps needed.

[barehander]

I think I've told ya that here we utilize two different system voltages...7200/12470 and 12470/21600.

We have some delta high side banks on 7200 using the 12470/21600 pots. No taps needed.

Whoa......12/21 pots on 7200?

[Trojan]

Right. So, 7200 x 1.73 = 12,400. turns ratio is 7200 / 277 = 26. Connect primary phase to phase; 12,400 / 26 = 477.
Also; 277 x 1.73 = 480.

[rcdallas]

Whoa......12/21 pots on 7200?

Yes sir!

:)

[wtdoor67]

Getting all tangled up on this subject but I like sorting out stuff like this. Better than Dems. and Republicans.

Here's the way I understand it. Actually we've been on a similar subject before.

A 277/480 pot actually has only one secondary winding. That winding is 277 turns. Why they say 277/480, I don't know, but if you hung one pot alone, all you would get would get would be 277 volts if hung on the rated primary voltage.

Take a pot that is labeled 7200/12470 primary and 277/480 secondary. Now that pot would have 2 primary bushings with 7200 turns on the primary and 277 turns on the secondary winding. I don't know if the primary insulators would hack 12470 but I'm sure the inside would. Looked it up once. Anyway put her in there phase to phase and check secondary voltage. Since 12470 is 1.73 times 7200 that should hold the same for the secondary winding. It should read 480 TO GROUND. If you managed to hang 3 pots in this manner the 3 phase voltage would read 832 phase to phase. This would be a Delta/Wye hookup. The only Delta/Wye hookup I've seen similar to this was using pots that had the approximate primary amount of turns as the voltage being accessed.

[Trojan]

I was with you until you said "to ground"'you'd get 480 at the sec'y bushings. I guess you could connect one bushings to ground, but I was thinking about connecting to other transformers to make 480 delta.

[Pootnaigle]

Ummmmmmm fergive me but I sho nuff never had the cajonies to increase the primary voltage on nuffin I ever hooked up. If'n the pot said it was fer 7200 aint no way I wud hook er up on a phase to phase voltage of 12470. Be pickin up peices of that thang fer days.I reckon my original question shoulda been If'n ya hadda480 power bank hooked up on 13.2 and built wye delta and ya hadda convert the system to ummmmm 34.5 couldnt ya just use 277 pots and build it wye- wye n float the secondary neutral buss, ground one hot laig, rotate the old and the new, take an outage and swap em over? Me I bleve it wud werk jus fine.

[Trojan]

Tha's what's we do now, Snuffy. Just getting imaginative with transformer conneckshuns.

[wtdoor67]

I was with you until you said "to ground"'you'd get 480 at the sec'y bushings. I guess you could connect one bushings to ground, but I was thinking about connecting to other transformers to make 480 delta.-----------------------------------------------------------------

If you could get this contraption to hold a fuse I agree you could probably make a 480 delta secondary of it. If it was a 480/832 hooked Wye then I guess it would make a 480 Delta. I doubt if you could ever find such a lashup, but it's interesting to talk about.

However if you were in some far off corner of the world and ran across the need for such a thing and could dream it up it might get you out of a bind. Who knows?

[wtdoor67]

Once I did see a 3 pot bank hooked Delta/Delta. The pots were labeled 7200/12470 and the secondary 240/480. The primary was 7200/12470. The bank was supposed to be hooked Wye/Delta with the high side of course "floated". Hooked Delta/Delta it wouldn't hold a fuse so I doubt if you'll get to try this Trojan. Course with an Extendo stick a person can try lots of things. Heh.

Oh yeah, I remember some pots labeled 2400/4160 in a Delta/Delta configuration that were tried on a 4160 primary. They wouldn't hold a fuse either. Old contractor that tried this had blown a lot of fuses from the number of empty fuse boxes lying on the ground.

[Trojan]

I meant what pootnaigle said when I said that's what we do now. Wye-wye replaces wye-delta 480v. It helps to know turns ratio, test results, ET cetera, for trouble shooting.
You're right about being stranded and having to rig something up. They used to make up all kinds of head scratchers in Chgo on the 4kV system. Increase kVA by paralleling 2 same size xfrmers and next time you see increased kVA by connecting 2 same size xfrmers in series. The must have brought out Engineers to plan out connections cause that big copper wire was perfect.

[barehander]

[quote=Pootnaigle;101273]Ummmmmmm fergive me but I sho nuff never had the cajonies to increase the primary voltage on nuffin I ever hooked up. If'n the pot said it was fer 7200 aint no way I wud hook er up on a phase to phase voltage of 12470. Be pickin up peices of that thang fer days.quote]


That's what I'm sayin.......I call bullsh!t.....

[rcdallas]

I think one of the key things we're missing here to determine what can be hooked delta is the name plate.

If on the HV portion of the label says strictly "12000" it designates a 2 bushing transformer that can only be hooked up delta.

If the label says "7200/12470GRDY" it means that it's a single bushing transformer that can only be hooked up 7200 phase to ground. The GRDY also means the other end of the winding is grounded to the tank.

If the label says "7200/12470Y" it means that it is a two bushing transformer...it can be hooked up 7200 phase to ground provided that you ground the H2 bushing. It also means that you can hook it up delta on a 7200 delta system or even hook it up high side delta on a 4160/7200 wye system.

I mentioned earlier we have on our 7200/12470 portion of our system some high side delta connected banks that consist of "12470/21600Y" transformers.

Edit:

On the above given "12000", I don't know why it can't be hooked up on a wye system, I'm just going by what my grunt book says, the phase to ground voltage is 6936, so if you had a wye system that was basically 6930/12000 I don't see why you can't hook it up. My guess is that you can.

[Fiberglass Cowboy]

To cut through the Bull $hit ..... YES, either way will work.

Float the secondary neutral bus. Will work WITH or WITHOUT a hot leg grounded on 480v wye.

Grounded leg bank connection will read on hot legs: 480v; 480v; 0v - 480 v phase to phase. But will work fine on 3 phase applications requiring straight 480v.

No grounded leg, but secondary neutral bus tied together and floated; hot legs will read : (277-480v various, uncertain, unstable) on each leg, - 480v phase to phase. Will work fine on 3 phase applications requiring straight 480v.

The best application for either bank connection is for a perfectly balanced load (i.e. motor load only - as in a sewer lift station or a similar motor load) otherwise; an inefficient use of transformers. But some companies will utilize these connections for 480v motor load to avoid having to carry (stock) 240/480v transformers.

Try it.;)

I will double check tomorrow. Both of these are in our transformer connections and theory book from work. If I am wrong I will re-post the correct info. :cool:

[Fiberglass Cowboy]

That was correct. I will type in the quote straight from the book for 480 volt, 3 phase, 3 wire connections (no secondary neutral) using 277/480 volt, (2 secondary bushing) transformers.

The book assumes the ungrounded phase connection as it is written.

" The voltages measured between the three phases are 480 volts, the voltage reading from phase to ground will vary. There is no electrical connection between the wye connection and ground, unless it is by accident OR intentionally grounded. If one phase is grounded, the voltage measured from phase to ground will be 480v, 480v, and zero (0) volts. There can be a voltage measured between the three phase and ground under certain circumstances. This voltage would be 277 volts, (or 480 volts divided by 1.73). This voltage is referred to as a "phantom" voltage. All of the conditions pertaining to the 277/480 volt, three phase, four (4) wire connections are the same for the 480 volt, three phase, three (3) wire connections. "

Also this bank will NOT parallel with any 480 delta bank, according to the book. It will always be 30* degrees out of phase (vectoring), as the transformer is wound for a wye connection.

- Hope this helps ......... :cool: