OT: 208 boost to 240 or 480 step down?

[monkeyhead]

This is off topic, but I'd appreciate any insight you guys have.

We just got a new lathe for our shop that needs 3 phase 240VAC. I'm familiar with using buck/boost transformers to boost a 208 circuit for this purpose, but I'm damn near at capacity in my 208Y/120 panels, so I'd prefer to step down a 480 circuit instead.

Is the cheapest way to do this with three single phase step down transformers in wye-delta like the above diagram (source page: http://www.elec-toolbox.com/usefulinfo/xfmr-3ph.htm)? Or is there a better [cheap] way to go about this?

 

[TConnolly]

Chances are a transformer made for the purpose will be less expensive. We had to do this once for a 15KVA load and the transformer was surprisingly inexpensive - IIRC it was an acme transformer. Have a look at this:

http://www.acmepowerdist.com/pdf/Page_25.pdf

 

[Thomas Sullens]

Just buy a 480 to 240 3 phase transformer. There are lots of used ones for sale also. We have bought several from Weaver Electric in Denver Co., but frieght has gotten to be an issue.

2 cents

 

[504bloke]

If the 240V 3 phase machine needs a neutral you will need a star (Wye) secondary (not the delta in your pic), You should get about 127 Volts to neutral (star). We did this for a Jap machine a few years back.

I would suggest the nicest/cleanest method is a new 3 phase unit.

 

[DickDV]

I've found that three phase transformers under 7.5KVA are a bit hard to find. If your machine is smaller than that, using three single phase transformers might be cheaper. Otherwise, buy a proper three phase unit.

 

[TConnolly]

If the 240V 3 phase machine needs a neutral you will need a star (Wye) secondary (not the delta in your pic), You should get about 127 Volts to neutral (star). We did this for a Jap machine a few years back.

I would suggest the nicest/cleanest method is a new 3 phase unit.

The ACME transformer on the catalog page I linked has a center tap between two legs on the delta secondary. This can be used as a neutral tap to provide 120VAC if necessary. This is a fairly common method in the US, esp. in residential power distribution, though I'm not sure how often you would see it on your side of the pond in the UK as you are 415/240. The center tap results in a high leg (208 V to neutral) between the junction of the two untapped windings opposite the tap on the delta secondary, which must be marked so that it is not accidentally used.

Here, most common wye transformers with a neutral tap drop to 208V for 120 line/neutral - something the OP already has.

 

[504bloke]

The ACME transformer on the catalog page I linked has a center tap between two legs on the delta secondary. This can be used as a neutral tap to provide 120VAC if necessary. This is a fairly common method in the US, esp. in residential power distribution, though I'm not sure how often you would see it on your side of the pond in the UK as you are 415/240. The center tap results in a 208V high leg between the junction of the two untapped windings opposite the tap on the delta secondary, which must be marked so that it is not accidentally used.

Here, most common wye transformers with a neutral tap drop to 208V for 120 line/neutral - something the OP already has.

The Pond over here is now 400/230.

The majority of transformers i come across are Delta Primary, Star (Wye) secondary with the star point being neutral and earth bonded.

I have seen delta tapped secondarys here, but they are not the norm for power/distribution transformers.

And sorry i missed your link

 

[TConnolly]

The Pond over here is now 400/230.

Thats right, you have been "harmonized." But I think the tolerance was opened up so that you could still have 415/240 and still call it 400/230 without having to actually redo everything.

 

[504bloke]

Thats right, you have been "harmonized." But I think the tolerance was opened up so that you could still have 415/240 and still call it 400/230 without having to actually redo everything.

Thats a nice word "harmonized", complete bollox is another

 

[monkeyhead]

Thanks guys!