Star-delta verse Dahlander 2

[itsmoked]

Got someone asking me to change a 460V 30HP screw air compressor over to 230V. Ugh!

No manual.

So I pull the cover and instead of a VFD I'm granted this:

The motor, being hard to get to, I'm trying to figure out if they're doing a low/high Dahlander or this is just a S/D since it's 30HP (94A @ 460).

I figure I can look up the two and quickly figure out which one I'm looking at.

But noooOOOOooOOoOOooo!

Here's the Dahlander

And here's the S/Delta

They're identical! Except inside the motor.

Yes, I see that they swapped two phases in the S/D but the same drawing is around without those two not swapped as they do it at the motor terminals instead.

I figured, "well if it's S/D then they need a timer, I'll find that to confirm it".
No joy, as the whole thing is run from a black box which is the front control panel. Could be a timer could be a Dahlander load adjuster.

Back to the entire point though. In either case would this thing be dual voltage if it has only six leads? Can't be can it?



Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Star delta:
There will be continuity between U1 and U2.
There will be continuity between V1 and V2.
There will be continuity between W1 and W2.
Dahlander:
There will be continuity between all six leads.
Was that the question?

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[che12345]

Dear Mr itsmoked,
1. It is likely to be a S/D as it has only one (1) [thermal over-load unit] located at the extremely right hand side. But, I don't see a timer.
1.1 Could it be that the (change-over time) is "manually" controlled by a [drum or S/D switch]?
2. If it is in Dahlander formation, it would have two (2) thermal over-load units as shown in your circuit.
3. It would be essential to read the motor name-plate data, no matter how difficult is to access it. All what we can say are guessing.
Che Kuan Yau (Singapore)

 

[itsmoked]

I don't know if that was the question Bill.. But you make an excellent point. I could check that.


Hello Mr Yau. I don't see any overload..? The far right thing is the control transformer with a couple of fuses and some additional fuses between the transformer and the right contactor.

No drum switch, an electronic control unit.

I don't see an overload anywhere nor even a current coil.


I'm afraid you're right about seeing the motor plate.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Found a manual for the machine but of course the ONLY thing left out is the schematic.

I did see this:

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

It looks like transformer time, Keith.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Palletjack]

Found a manual for the machine but of course the ONLY thing left out is the schematic.

I did see this:

I don’t think 6 seconds is a long time for an air compressor. Is it?
Some fans are 10-15 seconds.

 

[TugboatEng]

If this is a one off project, surplus transformers are CHEAP, like $10 per KVA.

 

[badservo]

94A @ 460V doesn't sound right for a 30HP motor so you may want to verify that if picking a transformer.

 

[jraef]

Yeah, your current is way off, either that's the current at 230V, or it's a 75HP motor at 460V.

That panel does not appear to be built to NEMA / UL standards, it was likely built to IEC standards. So under IEC rules, they can have an adjustable thermal-mag circuit breaker feeding this starter unit and the adjustable thermal setting will function as the motor thermal OL protection. We couldn't do that here under UL rules until very recently (the breakers are now called Motor Protection Circuit Breakers or MPCBs and are listed under UL489, so they can be used as Branch OCPDs). But to use an MPCB in that manner, it would have to be in the same box as the motor starter, otherwise it is a "feeder" and is not listed as such. Anyway, this is just to explain why you may not be seeing an OL relay, it might be up stream.

The lack of a transition timer would be the tell-tale sign of it not being Star-Delta, but then you posted the controller, which may be handling that function too. So finally, that data sheet showing the "Star/Delta time" is likely the determining factor, that and the fact that having a 2 speed Dahlander motor on a compressor is somewhat pointless.

Now... whether that motor can be reconnected as 230V is another story... It would have to be 12 lead for an IEC motor to be capable of being connected as dual voltage. If that's the case, you would have to up-size the contactors , conductors and circuit breaker.

If it only has 6 leads, it can be Star-Delta start for a single voltage (usually High), or Dual voltage by connecting Start for High voltage, Delta for Low voltage, however it cannot be used both ways (dual voltage AND Star-Delta starting).

If it is dual voltage capable, then you have another problem: the V/Hz ratio is going to be wrong. IEC motors designed for (nominal) 400V 50Hz have the same V/Hz ratio as 480V 60Hz, 8:1. But if you reconnect the motor for 230V, that is 230V 50Hz, so the ratio is 4.6:1, and you will be giving it 240V 60Hz, with a ratio of 4:1. The result will be under flux in the motor, so significantly less peak torque (75% of design) and about 86% of running torque, so more slip and higher current / heat under load. That's not to say it wont work, it probably will (unless the OEM designed the motor size too close to the bone), but it will likely fail earlier than normal.

So to Bill's point if you put a transformer ahead of it and leave it as a 480V system, you don't need to change anything else and can expect normal life from the motor. That's what I would recommend. If the motor really is 30HP, I would put a 75kVA transformer ahead of it (minimum). If it is 96A, I would go yo 150kVA.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[waross]

If this is a star delta start, for a 460 Volt motor, the delta voltage will be 460 Volts.
If you use the star delta for dual voltages the voltages will be delta:- 460 Volts, star:- 797 Volts.
Not really useful.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

badservo et al; 94A seems way off-base right?

It has a separate fan for the heat exchanger but I doubt it's more than 1hp.

This label is inside and you can see the edge of it in my first picture at the top of the thread.

And here's the EXTERNAL plate:

I looked at the outside "460V" then opened the machine and saw the "93A".
Now I see the inside plate stating "200V".

30hp @ 200V = 80A.
Yet you feed this machine 460.. There are no transformers anywhere.
Why oh why would they label it 460 outside and 200 inside?

This is in the manual. I think this is what Jeff's talking about. No protection in the machine at all and you're supposed to follow these instructions and reading carefully between the lines provide it outside. "if the 'switch' doesn't provide overload protection add fuses". Cripes!

I so love Chinese quality work.

Thanks all for the great info. Thanks Jeff for the detail.


Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Dahlander changes speed, star/delta doesn't. That's all I got.

Muthu

http://www.edison.co.in

 

[itsmoked]

edison123... You've got a lot more than that!


Back at college I wouldn't have agreed with your statement!
A lab I inhabited in the basement had two big CenTraVac chillers next to it. It was my introduction to star-delta starting. Those babies would start up in star sounding like a monster vacuum cleaner and just as the speed topped off at some crazy high speed there was a loud 'CLACK' and they'd spool up to what sounded like three times faster yet, finishing out at an idling jet engine sounding speed.

Keith Cress
kcress -

http://www.flaminsystems.com