2 phase 208 to 3 phase 230

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Maynard

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My customer wants to run a Heidelburg press, 3 phase motor, 1.65Kw, wired for 240 volt operation. His shop was wired for 120/208. He has a Roto-Phase converter Model M (Max total HP = 7.0). It seems that he may need one or two buck transformers to raise the input high enough to run the Phase converter. I have not installed buck transformers and am not sure if they simply are wired in series with the input line, or what.

Is my explanation clear enough with enough facts to get some advice?
Thanks.
 
Step 1) Look very closely at exactly what the motor nameplate says. Does it really say specifically 240V? Or does it say 230, or 220? It makes a difference.

If it says 220 or 230V, it may be fine to run it at 208. Most motors can tolerate +- 10% of nameplate rating. So 230 * .9 = 207V but 240 * .9 = 216, so if the nameplate truly says 240V, then you have to go with the Buck/Boost XFMR.

Step 2) Again with the nameplate, double check the frequency. Some Heidelbergs came from Germany direct with 230V 50Hz motors. If you put 60Hz on it, the speed will go up 20%, and that can be problematic on a press.

Step 3) If you need a XFMR, buy a new one that comes with a manual on how to connect it. Flea-bay stuff often is missing the manual and the money you save needs to be compared to the value of your time. It's not difficult, but it is time consuming to try to figure out which lead is which on a buck/boost transformer connection if you don't have the manual.
 
Smart beat me to it. If you've got 3-phase already, use it, even if you have to add the third phase. If you're getting 208 and not 240, there's 3-phase real close by.

I was gonna say (so I will) that I wouldn't try cascading rotary converters and BB transformers. It's so Frankenstein!
frankenstein-smiley-02.gif
Use the one device that does what you need.
 
Smart $ said:
Please clarify shop's power configuration...

120/208 1? 3W

or

208Y/120 3? 4W
Click to expand...

It is absolutely imperative that nameplate specs of the machine match up to the power supply it is installed on. Pay attention to control voltage requirement.

But, because the OP said he was using a 'phase convertor', I am going to work on the premise that he knows he has single phase power.

Many European machines are actually built with 60Hz equipment when their final destination is the US and 240V 3PH is not a common industrial voltage in Germany.

Now back to the original question - How/where to install a buck-boost transformer.
Yes, effectively it is installed in series with your load.

I do not like using buck-boost transformers or phase convertors to supply loads that require a L-N voltage for their control power (i.e. they are 3PH 4W). I also prefer the new generation of 'digital' phase convertors (I have use some from Phase Perfect) to power machines with drives and servos, I only the rotary kind on pure motor loads.
 
jim dungar said:
...
But, because the OP said he was using a 'phase convertor', I am going to work on the premise that he knows he has single phase power.
...
Now back to the original question - How/where to install a buck-boost transformer.
Yes, effectively it is installed in series with your load.

I do not like using buck-boost transformers or phase convertors to supply loads that require a L-N voltage for their control power (i.e. they are 3PH 4W). ...
Click to expand...
I just want to verify he is working with 120/208V 1? 3W... because I'm of the impression BB xfmr(s) will not solve the problem if the machine needs 240V 3? 3W.

Can a BB xfmr be connected on a 120/208V 1? 3W system to get a 240V 3? 3W output?

I'm more inclined to go with two 120-240 1? step-up xfmrs connected for an open-delta 240V 3? 3W ouput. To get phase angles correct, one xfmr has to be connected reverse polarity.
 
Smart $ said:
Can a BB xfmr be connected on a 120/208V 1? 3W system to get a 240V 3? 3W output?
Click to expand...
No way. That idea was to use a BB to step the 208v up to 240v, then a rotary converter to derive the 3-phase power. There would be no true neutral available with a single BB.

I don't like the sound of it, but I guess there's no electrical reason it couldn't work.

I'm more inclined to go with two 120-240 1? step-up xfmrs connected for an open-delta 240V 3? 3W ouput. To get phase angles correct, one xfmr has to be connected reverse polarity.
Click to expand...
Now, that sounds more like fun. This would also provide no neutral, unleee you create a high-leg, but I think you'd get a better 3-phase supply.

A VFD maybe?
 
LarryFine said:
... There would be no true neutral available with a single BB.

... This would also provide no neutral, unleee(< ?) ...
Click to expand...

So far he's not indicated a neutral is required... besides, most 3? 3W machinery utilize its own control xfmr with a line-to-line primary and one leg or a center tap grounded for the control common/neutral.
 
Update on phase converter and buck-boost transformer.

Update on phase converter and buck-boost transformer.

Thanks for your responses. Sorry for the delay. We,ve been a little pre-occupied, what with Mount Redoubt puffing ashes all over the Kenai peninsula.

The Heidelburg press: Previous installation was served by 120-240 4 Wire. The 3 phase motor is made by Siemens. I have communicated with them and they say: "This motor cannot be run at 209, you must use 230V". It does include a control system which needs 2-wire, 120 volt.

The shop: Is located in a complex of eight small businesses. The initial installation was supposed to be 120-240, 4 wire, delta. But it turned out differently. All businesses have single phase, 120-208. I've interviewed some of them and they don't realize that they have 208, not 240. No body every cared until my customer came along, with a three phase press. To properly supply this customer, the power company would have to put in a 3 phase meter, and run another wire the length of the building. Not going to happen.

ARCO has supplied drawings that show how to install the Roto-Phase with a Buck/Boost transformer.

I'm uncomfortable with the neutral situation and the single phase control feed.

The customer already has the Roto-Phase. By the time he pays for a buck/boost, a mag. starter, disconnect switch, cabinet, and wiring he is going to be in for a lot more bucks than he figured on.

Thanks again. All advice gladly accepted.

Maynard.
 
RE: 2 phase 208 to 3 phase 230

Thanks for your replies. Sorry I didn't get back to you all right away. We have been a bit distracted up here, what with Mount Redoubt volcano blowing it's top.

You are right, the service is rightly named "120/208 single phase". I called it "2 phase" because if I could get one more wire in there, I could get "3 phase".
The customer has a "unit" in a multi-business commercial mall. According to the power company the mall was supposed to be wired 120/240 3 phase, 4 wire delta. But it didn't turn out that way. None of the other businesses in the mall were aware what service they had, and did not care. Even the mall manager did not know what he had.

I copied the Heidelburg press motor name-plate info to Seimens. They said simply: "The motor cannot be run at 208, you must use 230V".

The press was previously installed in a shop with 120/240, 3 phase, 4 wire, open-delta. The press is designed for 60 hz operation.

ARCO has supplied wiring diagrams for the Roto-Phase connection with a Buck/Boost transformer.

My concern now is with the feed to the 120v control system. I have to have a neutral for that hookup.

This is getting more complicated and expensive than my customer counted on. I'll need a mag starter, a disconnect switch, a cabinet, plus commercial-grade wiring, all in conduit.

Thanks again,
Maynard
 
Is the machine fed with two different sources?
If so, you can continue to feed it with two different sources.

If it is fed with one source, and it contains a control power transfromer you can continue to feed it with one source.

But if it is fed with a single 4 wire source now, you need to be careful in how you create your 120V source. Can you change it into a two feed machine? Can you keep it a single feed and add a control power transformer? It will be all but impossible for you to use a rotary phase generator to create a 240/120 3PH 4W supply.
 
jim dungar said:
Is the machine fed with two different sources?
If so, you can continue to feed it with two different sources.

If it is fed with one source, and it contains a control power transfromer you can continue to feed it with one source.

But if it is fed with a single 4 wire source now, you need to be careful in how you create your 120V source. Can you change it into a two feed machine? Can you keep it a single feed and add a control power transformer? It will be all but impossible for you to use a rotary phase generator to create a 240/120 3PH 4W supply.
Click to expand...

Aside from sizing and availability, what do you think about a two-transformer solution?

2XFMRsolution.gif
 
Smart $ said:
Aside from sizing and availability, what do you think about a two-transformer solution?

2XFMRsolution.gif
Click to expand...
You list your transformers with 208V primaries but you are connecting them to 120V sources. But yes, in theory, you should be able to go from an open-wye to an open-delta.
 
Smart$,

That is almost exactly the configuration that I was going to suggest. However I believe that the transformers need to have 120V primaries, not 208V primaries; the L-N voltage is only 120V. Also I believe that you need to swap the polarity of one of the transformers; as drawn you have an open wye to open wye configuration, with a center tap on one of the legs of the secondary wye.

Maynard,

The term '2 phase' raises red flags in discussions because it is often misused. However, while you nominally have 'single phase' service to these businesses, this 'single phase' service is really composed of two legs of a three phase service. Because you have two legs of the three phase service, you can use transformers to 'regenerate' the third leg.

As you note, if you use buck-boost transformers, the relationship between the phase terminals and neutral can become quite asymmetrical; if you only need the line-line voltages then this may be acceptable. But if you have line-neutral control circuits, then you must be very careful about using buck-boost transformers. Often is makes more sense to use a simpler fully rated transformer arrangement rather than use buck-boost transformers; this makes the wiring clearer and simplifies OCPD layout...but means larger transformers with greater losses.

In any case, if the 3 phase load is really only 1.65kW, you can produce proper 3 phase 240/120V with a grounded center tap, using a couple of small transformers.

-Jon
 
jim dungar said:
You list your transformers with 208V primaries but you are connecting them to 120V sources. But yes, in theory, you should be able to go from an open-wye to an open-delta.
Click to expand...

Ooops.... I was in a rush to get the drawing done. Nonetheless, you are correct, it should be 120V primaries.
 
winnie said:
...Also I believe that you need to swap the polarity of one of the transformers; as drawn you have an open wye to open wye configuration, with a center tap on one of the legs of the secondary wye.
Click to expand...

Are you sure? The primaries are wired reversed polarity. Note N connects bottom of T1 primary and top of T2 primary. In essence, that inverts the L2-N winding from -120? to +60?. See diagram below (primary voltage corrected)...

2XFMRsolution2.gif
 
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