Go a call to install an air compressor in a shop that I found has a delta system in it. The compressor is 277/480 but the Delta is 120/240 with a wild leg. Ideas?

What size is the motor? Does a frequency converter make any sense?

The motor itself is a three phase load, and doesn't know from wye or delta on the supply. It is _probably_ a dual voltage motor which could be re-connected in the terminal box to operate from a 240V supply. Of of the control/overload/protection hardware would need to be suitably re-configured or upgraded for the increased current and reduced voltage.

-Jon

I'm a little confused by something.


Assuming the compressor is 3Ø 3W, you don't utilize a neutral so there's really no 277V involved.

Assuming the compressor is 480V 3Ø 3W, and assuming it's not a dual voltage motor (480V 3Ø & 240V 3Ø), then with a 240V delta system I think you're pretty much looking at installing a transformer to match the supply voltage to the compressor.

Radar

In Europe a standard 230 / 400 motor can be star wired to match 3 x 400 and delta wired for the rare 3 x 230 grids.

It will mostly have six terminals and three jumpers to adjust it to local situation.

You do that in a different way?

Even when a motor is star connected, the neutral of the motor does not get connected to the neutral of the supply.

Common three phase supply voltages in the US are 208V, 240V and 480V, so there you don't find a common situation where you will want to switch a motor between star and delta.

Instead you see motors where there is a factor of two voltage difference between the different possible motor connections, eg 240V or 480V.

-Jon

@ winnie

mshaw says it is a 277/480 motor. This is nevertheless a typical star / delta ratio. Who knows where it comes from. Only mshaw can tell us whether it's got six terminals.

As a matter of fact I fully agree with you that it might be possible to run the motor delta wired at 240 with a remaining risk that it will burn due to overheating caused by low voltage.

We need some more info on the compressor.
If it's just a motor and belt driven compressor it most likely has a nine lead motor which can be hooked up as 460 volt or 230 volt.

Frequency converter?

We have already installed frequency converters only to adjust local low voltage to motor nominal voltage. This is more a side effect but with small motors easier than a transformer, particularly interesting to run small 3p400V motors on 1p230V.

Ahh, I get it. At least a few variable speed drives are capable of operating at an output voltage that is higher than the input voltage. For some applications it might make sense to install a VSD simply for voltage control, leaving the frequency conversion aspect of the device as a nifty side effect. Note that _most_ VSD systems are not capable of _boosting_ the output voltage significantly above the input.

-Jon

As the converters typically work with an intermediate DC circuit at (root)2*ACvoltage, it is not very difficult to realise. DC is then switched according to what the motor needs, voltage and frequency can (but not necessarily) be varied in wide ranges as long as the motor survives it.
It is a price, space, and EMC discussion.

(edited for Germanism)

[This message has been edited by Wolfgang (edited 02-03-2006).]

This is a small mom and paw shop with a used compressor let me check the leads and get more info. Thanks

Mike, can you get the nameplate info off the motor?

Dnk..

Ah..... A VSD type device, I'm with you now.

I just saw frequency converter and started thinking along the lines of fixed voltage rotary converter, or electronic equivalent.

Btw, Wikipedia doesn't know VSD at all!
But it knows: VFD, frequency converter, frequency changer.

European industry also sells it as (solid) fr. inverter! The older were rotating ones.

What a mess!

480 is a standard voltage. So are 240 and 208.
Why not just use a three-phase transformer? They work both directions, you know!