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.