# Do I have wye or delta?

• posted

Now that I'm getting some transformers to buck the voltage from my phase converter I need to determine whether the output is wired wye or delta. I think it's delta. but since it's a phase converter I just don't know and need to be sure. According to the Square D website the wiring is different between delta and wye when using the buck xmfrs. Delta only needs two xmfrs for example. So how do I determine what I have? I do know that leg to leg voltage is the same but that leg to neutral for the manufactured leg is not. The two lines supplied by the power company measure 124 volts to neutral and the manufactured leg to neutral is 230 volts. Thanks, Eric

• posted

Leg to leg voltages should around 240 volts.

The generated leg should make the system look like an open Delta.

But the supply being Delta or Wye will not affect the transformers. The transformers can however be wired int Delta or Wye....

IOW, you have a supply. It can be Delta or Wye.

Then you have the Buck/Boost transformers. They can be wired in Delta or Wye.

Don't confuse the two things.

• posted

Well maybe I just don't understand. The Square D website has wiring diagrams for both wye and delta SUPPLY according to my interpretation. However, I'm pretty sure I have open delta. Eric

• posted

Consider it as being a delta system.

• posted

-voltage-buck-boost.jpg

Eric it might be helpful if yiou link us to the applicable Square D conections diagram...

Also, strongly suggest that when testing any transformer connection, temporarily fuse the input side with a set of relatively low amperage fuses, say, 10 amps or so in order to protect the transformer for just in case you've made a serious mistake.

• posted

But Buck/Boost transformers act sort of like an autotransformer. There is no isolation between input and output so the voltages and phase relationships are a bit weird with delta wiring -- *unless* you use only two transformers and operate it as "open delta", and connect the low side of the two together, so the boosts are balanced. If you connect the third one in as well, you'll have weird things in terms of phase relationships. Of course, the generated phase from a rotary converter is already a little weird, so I guess that you can live with that. :-)

Good Luck, DoN.

• posted

Wait a minute - If you are starting with Residential 120/240V Single Phase that's coming in too hot, you need ONE Buck-Boost on the input to your phase converter to drop the voltage down to 240V.

Get the voltage right to the input of the phase converter, and let it handle making the third leg at the right voltage.

Wye, Delta or Open Delta only count when you're getting the 3-phase straight from the Power Company.

Most residential users with wells or elevators, or small Commercial like a strip mall gets 120/240V Open Delta - One big transformer on the pole for the 120/240 which is the bulk of your load, and a smaller transformer next to it for the Wild Leg.

The Wild Leg usually measures ~190V to ground, gets tagged Orange so you don't mess up and hook a 120V load to it. Because you hook up there and Light bulbs and ballasts don't last long...

Full Delta is usually straight 240V or 480V - three equal sized transformers.

Wye is either 277/480V or 120/208V - three equal sized transformers, but all the commons are grounded and becomes the Neutral point.

-->--

• posted

diagram...

temporarily fuse the input side with a set of relatively low amperage fuses, say, 10 amps or so in order to protect the transformer for just in case you've made a serious mistake. Here's the link to the Schneider Electric site:

Square D was bought by Schneider. The diagram I think I need to use is #5 on page 6. The xmfrs are the 1.5S46F model. I used table 15, page

19 to determine which wiring diagram to use. After looking at the above link again I'm sure that open delta wiring is what I have and need to use. Eric
• posted

Greetings DoN, I will be using two of the three xmfrs and wiring open delta. See this linl:

Wiring diagram 5, page 6 is what I'll be using. Will using buck xmfrs like this tend to equalize the voltages coming from the phase converter? Thanks, Eric

• posted

interpretation.

conections diagram...

temporarily fuse the input side with a set of relatively low amperage fuses, say, 10 amps or so in order to protect the transformer for just in case you've made a serious mistake.

You are confusing open delta with your single phase neutral.

The output from your phase converter is delta.

Forget that your single phase neutral even exists; it has no bearing whatsoever here other than it's happening to at the same refrence potential as your ground proper.

That said, it does looks like your diagram should work, suggest fuse the input side like I advised earlier, wire it up and double check to make sure the output voltages are as expected before actually connecting it up to your machine.

• posted

conections diagram...

temporarily fuse the input side with a set of relatively low amperage fuses, say, 10 amps or so in order to protect the transformer for just in case you've made a serious mistake.

here other than it's happening to at the same refrence potential as your ground proper.

side like I advised earlier, wire it up and double check to make sure the output voltages are as expected before actually connecting it up to your machine. I will be doing as you suggest, using fuses and checking voltages. Eric

• posted

[ ... ]

diagram...

temporarily fuse the input side with a set of relatively low amperage fuses, say, 10 amps or so in order to protect the transformer for just in case you've made a serious mistake.

O.K. Using *that* diagram, you will *get* open delta, even if you aren't starting with it. Your rotary converter may be wired as delta or as wye, and in most cases it should not matter.

Two things to consider:

1) The diagrams shown are to provide boost. If you want buck (to lower the voltage) you want to interchange the joined X2 & X4 with the joined X1 and X3, all other things being the same. 2) If you want full wye, go to diagram 9 on page 7 (this requires you to have a generated neutral from the rotary converter -- which will be hot compared to the incoming neutral, so it is probably not a good idea.)

But -- if the transformers are big enough, you could use *one* of them on the single phase *input* side before the rotary converter and have the same effect -- as another poster suggested yesterday I believe.

If you need a bit more current, use two of the transformers wired as in diagram three (also page 6) and parallel the input and output points.

Good Luck, DoN.

• posted

I just posted a followup to an earlier posting of yours containing this URL -- suggesting three ways to go, of which your diagram 5 is one.

Probably not. Unless you used the wye connection and selected to not boost one of the three phases (assuming that is is high).

But -- have you considered putting the buck-boost on the input side to the rotary converter (thus only one buck-boost transformer, unless you need two or three in parallel) so you reduce the voltage to *all* of your machines to normal levels. Someone else suggested this in an earlier followup in this thread, and I consider it the best choice, if you have enough capacity in the buck-boost transformers to handle the worst case load.

Good Luck, DoN.

• posted

conections diagram...

temporarily fuse the input side with a set of relatively low amperage fuses, say, 10 amps or so in order to protect the transformer for just in case you've made a serious mistake.

Actually, you just swap input and output.

He does not.

938-4564

• posted

conections diagram...

temporarily fuse the input side with a set of relatively low amperage fuses, say, 10 amps or so in order to protect the transformer for just in case you've made a serious mistake.

DoN, Now I'm confused again. Looking at the diagram it lists HV and LV. So don't I wire everything just the way the diagram is and connect my phase converter to the HV points and the machine to the LV points? Regarding using the xmfrs before the phase converter I need to be able to run 45 HP. That's when all my machines are running. And I have had all of them running at once. Not very often though. Would three of the xmfrs in parallel do the job? Anyway, all my other machines have the taps in them to allow running at the higher voltage. In fact, the machine in question has taps on the control xmfr that allow the control portion to run at the higher voltage. But the VFD does not. Thanks, Eric

• posted

No, you reverse the polarity of the secondary winding to change between boost & buck.

• posted

Well ... you could do that, but it would be working as an autotransformer, not a buck-boost transformer, and the voltage adjustment would be a bit less than you would get wired in "buck" mode. (Exchanging the pins which I mentioned above.) Whether it would get you close enough -- or even closer to your target voltage than the buck mode

-- remains to be seen.

If you have the full 240 V applied to the primary (two primaries in series, based on that diagram), you will have the transformer ratio determining the voltage out of the secondary, which will either add to or subtract from the 240 V.

However, if you connect the 240 V to the other end of the secondary wired in "boost" mode as shown, you will have less than 240 V applied to the primary, so your adjustment output will be smaller. This

*might* get you closer to your desired voltage -- I just don't know. I remember that you had the voltages you wanted and the voltage which you really had in place of the 240 V in earlier articles, but I don't have those available now. Same for the current and voltage ratings on the buck-boost transformer.

Boost mode is when the voltage of the secondary adds to the mains voltage coming in. Buck mode is when it subtracts from that voltage coming in. Autotransformer mode is like boost mode, and what you will get is a function of the winding ratios. (And yes, it does reduce the voltage if you interchange the HV and LV points on the shown wiring, just not as much as when wired in buck mode.

Ouch! That adds up to about 140 A from the single phase 240V.

Will one of them deliver about 47 A from the two paralleled secondary windings? You've got the transformer nameplate to look at, I don't.

A pity that the control transformer does not have a big enough core to handle the VFD as well -- to allow tweaking the voltage to it.

So -- I guess that you use the two transformers, and see whether they do what you need.

Good Luck, DoN.

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