WYE vs Delta Motor Windings

[EmagSamurai]

Is there a performance and/or reliability difference to consider when choosing a WYE wound vs delta wound motor? I was told last week that a WYE wound motor acts like three separate windings and pushes the rotor while a delta wound motor acts like one continuous window and drags the rotor. Also, in this same conversation I was told that wye wound motors are less efficient than a comparable delta wound motor.

I've never heard anything like this before. The business about pushing or pulling the rotor seems to completely ignore the physics of how a motor works. The stator field is always rotating faster than the rotor, correct?

My understanding is WYE wound motors can be built a little smaller, hence they tend to be used in smaller motors (say somewhere around 25 hp and below, but not a fixed rule). Otherwise, the characteristics between the two are similar.

Did is I miss the day this was covered in Power class? ?

 

[Smart $]

Let's put this myth to bed.

Consider a 240V 3Ø 6-lead motor connected to a 240V 3Ø 4W high-leg delta. Now consider connecting that very same motor to a 415Y/240V 3Ø 4W (60Hz) system.. How would you connect it? What difference would there be in motor performance?

 

[Jraef]

Whomever told you that was likely making it up.

There is no real difference in the way it operates. Whether the rotor is pushed or pulled is totally irrelevant. Forget that crap. But if you are curious, technically it's both. You can't have less than two poles, so as one field is pushing one pole, it's also pulling the next one.

Torque is created by current. So if you want more torque, you need more current. If a motor is delta wound, it pulls the necessary current for the torque you need with smaller wire compared to a wye wound motor, favoring delta wound for larger motors. But if the incoming line voltage is unbalanced, a wye wound motor will help decrease the effects of that imbalance across the coils, so it will run cooler in that circumstance. In smaller frames, the curent values are low anyway so the consequences of the conductor size are less, and the consequences of having unbalanced voltages causing heating are higher. So wye is typically selected for small motors. How small is a matter of economics, different for each manufacturer because it affects the slot geometry, which affects the frame decisions etc.

Bottom line, you often have no real choice anyway.

What smart$ is referring to is that outside of North America, dual voltage motors are wound so that you can connect it in wye for the higher voltage, delta for the lower, so again, you really have no choice.

 

[Besoeker]

Whomever told you that was likely making it up.

Don't think likely comes into it.

 

[Sahib]

Is there a performance and/or reliability difference to consider when choosing a WYE wound vs delta wound motor? I was told last week that a WYE wound motor acts like three separate windings and pushes the rotor while a delta wound motor acts like one continuous window and drags the rotor. Also, in this same conversation I was told that wye wound motors are lesubs efficient than a comparable delta wound motor.

I've never heard anything like this before. The business about pushing or pulling the rotor seems to completely ignore the physics of how a motor works. The stator field is always rotating faster than the rotor, correct?

My understanding is WYE wound motors can be built a little smaller, hence they tend to be used in smaller motors (say somewhere around 25 hp and below, but not a fixed rule). Otherwise, the characteristics between the two are similar.

Did is I miss the day this was covered in Power class? ?

Yes there is a difference in performance. If both star and delta motors are wound for same line voltage and same rated speed ,the star connected motor will develop lower
torque and so lower HP rating.

 

[Besoeker]

Yes there is a difference in performance. If both star and delta motors are wound for same line voltage and same rated speed ,the star connected motor will develop lower
torque and so lower HP rating.

That wasn't the point.
And they wouldn't be anyway.

 

[EmagSamurai]

This forum is awesome! It's taken me a long time to join because I usually find the answers I'm looking for on here without having to post.

I appteciate all the feedback!

 

[Smart $]

...
What smart$ is referring to is that outside of North America, dual voltage motors are wound so that you can connect it in wye for the higher voltage, delta for the lower, so again, you really have no choice.

No, I'm not referring to anything regional. What I'm saying is a 3Ø motor powered by 240V 60Hz displaced 120° across each of its 3 windings has the same performance whether it is getting that power via a delta or wye connection.

 

[ATSman]

I found this interesting discussion on the subject:

http://forum.allaboutcircuits.com/threads/pros-cons-of-wye-vs-delta-motor-windings.64187/

 

[Jraef]

No, I'm not referring to anything regional. What I'm saying is a 3Ø motor powered by 240V 60Hz displaced 120° across each of its 3 windings has the same performance whether it is getting that power via a delta or wye connection.

Ah, sorry.

But now that you say that, what I think you are doing is referring to the INCOMING SOURCE power configuration being Wye or Delta for a give voltage, and you are absolutely correct.

I had interpreted the OP's question however to be referring to the INTERNAL configuration of the motor windings, which can be Wye or Delta as I described, but has zero relationship to what the SOURCE is.

 

[Smart $]

...
But now that you say that, what I think you are doing is referring to the INCOMING SOURCE power configuration being Wye or Delta for a give voltage, and you are absolutely correct.
...

No.... I think. Not quite sure what you are saying.

My incoming source power is only different to force the connection to be different, i.e. to keep the same voltage and relative phase angle across each internal winding.



Note the depicted system neutral connection is not required.

 

[ryknroll]

Motor Man Mark

Motor Man Mark

Just a little side note. Most of "US" motors(you know Company owned by Japan/Emmerson) come 6 lead "Wye/Delta". Start in Wye, Run in Delta. Not to say one is better then the other. Grew up in Motor shops since '77. True all small motors are Wye while larger 30HP and up are mostly Delta connected buggers. If you watch the windings going in they are all the same until you do the "grab one, skip 3" coil group connection ends. On and about "Why the Wye?". Small motors tend to be 220/440 Dual V. Wye circuits use all 9-leads same size. Whereas, Delta you would have 3 larger leads(#'s 1,2,and3) out of 9 pulling from a different spool. Easier to grab 1 spool, lol. Larger HP motors obviously don't use 220 Volt ie....Large leads, Starters, Protection etc. Sorry to barge in, just thought this hit home a bit. My opinion is they are close and is usually a product of Wires in hand,Turns in coil, Coils in group, and Coil tooth span giving the connection favorite. New motors are getting, well... efficient in their material procured. So final answer, to make a short story long, the real question is which one has the proper Back Iron, Tooth Width, and length to create the proper Flux Densities for it's torque and Horse Power Rating?:thumbsup: