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  #1  
Old 01-02-2012, 02:00 PM
Blue-Photon Blue-Photon is offline
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Default Pros & Cons of Wye vs. Delta motor windings.

What are the advantages / disadvantages of connecting a 3Phase motor in Delta vs. Wye?

(I have been searching for answers to this question for some time. All forums I've visited gave only half baked answers, so I'm hoping this one will be a little more professional.)

I have a small (0.75HP) 6 wire motor - currently connected as Y with center floating. The name plate states: Y/Δ, 230/380 VAC, which tells me I can configure it both ways. If possible I'd like to get more power out of it, so the question is will a Delta connection achieve this?

Many people have stated that there is no power (or other) advantage or disadvantage between the two connections, but if that is the case, why would so many (larger) motors use Wye-Delta starters? These motors clearly "kick-in" when they switch from Y to Δ. If there is no advantage, then why aren't all motors simple connected in Y, and left that way (Y/Δ starters are much more complex and expensive)?

Blue-Photon
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Old 01-02-2012, 02:38 PM
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strantor strantor is offline
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Your motor is meant to be connected Δ 230 or Y 380. When you connect Δ, you get full applied voltage across each winding. in Y, you get a voltage divider effect across 2 windings at a time. wye-delta starters are a "soft start" or "reduced voltage start" - they start out in wye, giving less voltage across each winding, and then switch to delta.

more info here http://samplecode.rockwellautomation...p004_-en-p.pdf
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Old 01-02-2012, 02:50 PM
jimkeith jimkeith is offline
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There is no power output advantage when connected Δ.
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Old 01-02-2012, 02:58 PM
Blue-Photon Blue-Photon is offline
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Hi Strantor,

Thanks for your quick answer. I fully realize and understand what you have stated, but this dosen't quite answer my question.

I understand that Vpp in Y = Vpp in Δ, and in Wye Vpn = Vpp/√3, so the voltage from phase to neutral is reduced by √3.

If what you have said is correct (that this motor is designed for Y380 and Δ230), then connecting in Delta 380 would definately increase the power, but it could also run hot and fry the windings. To my knowledge however there is no Δ230 (readily) available in Europe. We only have Y380 phase to phase (230 phase to neutral), and Δ380.

Blue-Photon

Last edited by Blue-Photon; 01-02-2012 at 03:28 PM. Reason: Correction
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Old 01-02-2012, 03:15 PM
jimkeith jimkeith is offline
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The winding current is unchanged in either connection--the phase current does change by the √3 factor.

The only advantage is being able to match your mains voltage.
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Old 01-02-2012, 03:25 PM
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GetDeviceInfo GetDeviceInfo is offline
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your question on wye/delta start has more to do with the nature of the load. The motor just converts electrical energy to mechanical energy. Considering Stantors comments, with a Delta configuration you'll have full torque applied instantaneously to the load. If the load has high inertia, this can be very hard on transmission components, and will result in extended starting currents on the motor, causing high heat generation. Motor overload devices are placed inline to protect motors from extended current draws and when properly sized, will prevent such starts. With the Wye connection and the subsequent reduction of voltage on the windings, your available horsepower is cut to 1/3 rating. This greatly reduces the strain on the drive on start up. Once the drive is up to some speed, it is switched over to Delta to obtain full rated HP.

Not all loads are of this nature. In fact most loads in industry can be started without HP reduction. Electronic softstarters are now being integrated with power contactors and the costs are giving them wider usage. I've seen Wye/Delta starters applied to drives down to 1 Hp.

The other concept is as Stantor mentioned. By reconnecting your windings, you have an option of source voltages that you can connect to. Some of the most useful motors in industry are dual voltage motors. These are not Wye/Delta, but the optional voltage is immensly usefull.

Quote:
I have a small (0.75HP) 6 wire motor - currently connected as Y with center floating. The name plate states: Y/Δ, 230/380 VAC, which tells me I can configure it both ways. If possible I'd like to get more power out of it, so the question is will a Delta connection achieve this?
Yes, but you cannot exceed your current ratings, so again it's more of a question, can you drive a bigger load? Yes, within the ratings of the motor.

With all that being said, you should probably give us full nameplate data, as you may have a multispeed motor.
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Last edited by GetDeviceInfo; 01-02-2012 at 03:34 PM.
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Old 01-02-2012, 03:47 PM
Blue-Photon Blue-Photon is offline
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Quote:
Originally Posted by GetDeviceInfo View Post
your question on wye/delta start has more to do with the nature of the load. ...
Yes (you will get more power), but you cannot exceed your current ratings, so again it's more of a question, can you drive a bigger load? Yes, within the ratings of the motor.
So if I understood correctly:

If I connect this motor in Δ(380) I will theoretically increase the possible power output.

If however in Y connection it is already reaching its maximum power rating, pushing it to Δ to deliver more power could (will) cause it to overheat.

This makes more sense to me.
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Old 01-02-2012, 04:28 PM
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Quote:
Originally Posted by Blue-Photon View Post
So if I understood correctly:

If I connect this motor in Δ(380) I will theoretically increase the possible power output.

If however in Y connection it is already reaching its maximum power rating, pushing it to Δ to deliver more power could (will) cause it to overheat.

This makes more sense to me.
yes. you could theoretically wire it in delta at 380V but you would have to derate it.
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Old 01-03-2012, 08:09 AM
Blue-Photon Blue-Photon is offline
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Thanks to all for your input & comments.

Things are much clearer for me now. It's nice to clear out a few cobwebs, since my EE courses date back 30+ years (I'm mechanical not electrical, but don't hold it against me).

Cheers, and happy new year!

Blue Photon

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Old 01-03-2012, 11:09 AM
jimkeith jimkeith is offline
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Quote:
Originally Posted by strantor View Post
yes. you could theoretically wire it in delta at 380V but you would have to derate it.
This will saturate the magnetics and probably will not provide significant additional torque. In saturation, the current will dramatically increase and overheat the motor. You must derate the voltage in this case--back to 230VAC.
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