Where do I find a 220v to 440v 3 phase transformer?

Where do I find a 220v to 440v 3 phase transformer? Can anyone post me a web address for such? I need to boost 220v to 440v for a Hardinge lathe. Thanks.

Greg

Hi Greg,

Grainger www.grainger.com stocks a range of transformers. You need to know the amperage or kva rating.

- Leigh

I got my 3KVA for 1 1/2 HP 440 motor at:

http://www.acmepowerdist.com/

It was just a Three Phase General Purpose Dry Type

Not as a 220/440, but as a 480/240

You hook them up "backwards" for step up service

John

surplus center

check http://www.surpluscenter.com. Their stock changes daily, so check back if you do not find what you want.

johnoder said:

You hook them up "backwards" for step up service

Click to expand...

Transformers don't always work correctly when wired backwards.

It's best to buy one designed to do what you want.

- Leigh

i get alot of good pricing on used stuff at EMSCO 763-571-9005

I'll agree... but disagree...

Leigh suggests finding one made for step-up service... I checked Grainger, and they have one (just ONE) for three-phase step-up service, 30kva, 208D to 480Y/277, for a meager $3600.

http://www.grainger.com/Grainger/items/1TBU7

Since it's WAY overkill, and you could throw away your lathe and buy a new Chineeeese one for that, I'd say no to that option.

There's a possibility you'd find such a unit surplus, but it's not easy, and even surplus, it won't be cheap.

Now, his reference to running one 'backwards'... sometimes that's the case, and sometimes not. An ordinary transformer doesn't know which way the power's going- it's a coil, inducing a field in a core, and another coil around same core, into which a current is being induced. in MOST cases, it doesn't matter.

Where it DOES matter, is when you have a specialty transformer that is designed to LIMIT it's own primary current... usually it is by having calculated, intentional resistance in one of (the primary side) the two windings... and sometimes they'll have specially made cores and even 'shunt windings' in the core. They're typically found in devices that require current-limiting over long-term, but surge currents in short-term. One of the applications that comes to mind is the Microwave Oven Transformer... and another is the Pole Pig (pole-top transformer). I've run these backwards, too (4CX250B, 4-1000A)... just hafta understand that they ARE 'special'.

But ordinary dry-types aren't current limiting... or if they are, I've never found one... I've found a few that naturally limited current because of a Non-Design related issue (burned out windings), but they had a diSTINKtive smell.

A 3kva 3-phase transformer will do fine... a trio of 1kva's MIGHT be easier and cheaper to find if you happen across an auction that has one lot of 'em... You'll have lots'a wires to figure out, but it'll work fine.

I suspect Leigh is referring to the type of transformer which has various losses "discounted" up front by adjusting the ratios to compensate for them. The secondary voltage may be made higher than the nominal ratio because of losses under load. If reversed, the step-up will be LOWER than expected.

That can throw the voltage ratio off when used in reverse, but the device does not "fail to work".

Greg:

You can use 2 or 3 single phase transformers.

As an approximation the KVA for delta connection per transformer for 3 transformers, assuming a balanced load, is full load leg current times leg-to-leg voltage divided by 1.732. For 2 transformers it its 3/2 times the value calculated for 3 transformers.

A high efficiency transformer will have fairly good reciprocity between primary and secondary interchange.

If a transformer has been given a voltage ratio different than the turns ratio, then you need to know if the difference is significant.

.

Might be a bit big but we have a few 15 kva 240/480 transformers in Rockford.

JST said:

I suspect Leigh is referring to the type of transformer which has various losses "discounted" up front by adjusting the ratios to compensate for them. The secondary voltage may be made higher than the nominal ratio because of losses under load. If reversed, the step-up will be LOWER than expected.
That can throw the voltage ratio off when used in reverse, but the device does not "fail to work".

Click to expand...

That's correct.

Transformers are designed with an open-circuit secondary voltage significantly higher than nominal loaded voltage, to account for IR losses internal to the transformer. If reversed, the output voltage will be lower than expected.

There's also an efficiency effect for transformers of standard design, i.e. primary on the inside and secondary on the outside. In this configuration, all flux lines developed by the primary cut the secondary. If you reverse the connections, some flux lines of the new "primary" will radiate out into space, not coupling any energy to the new "secondary".

And yes, the attached device will probably work, since the errors created are not large. But it may be of concern if the load current varies inversely with voltage.

- Leigh