How does the Delta Wye Switch Work? Help! 4

[DKirkham]

Dear Gods of Electrical Motor Theory,

I am just a lowly automotive/manufacturing guy most humbly petitioning you, the Gods of Electrical Motor Theory, to grace me with your knowledge on how the delta wye switch works.

Yes, I have searched Google. I have searched this site (you guys understandably gloss over it). I have searched high and low but can not find the answer to my question. I recognize my own electrical stupidity is probably hindering me.

If anyone had a few minutes, I would be most grateful.

I just read this

http://www.mmsonline.com/articles/wyedelta-in-perspective.aspx

My question is, does the delta/wye extend the torque range in a VFD 3 phase motor? How? and most importantly, why?

From the Haas website:

On-The-Fly WYE-DELTA Switching
Many Haas VMCs feature the Haas Dual-Drive
system, which consists of a dual-winding motor –
Wye and Delta – and an electronic switch to change
between the two windings. Selecting the best
winding for low-rpm cutting and the best winding
for high-rpm cutting yields higher torque over a
wider rpm range. The Haas Dual-Drive system also
provides constant horsepower over a much wider
rpm range, and on-the-fly winding change
provides the wide power range necessary for
constant surface speed cuts.

David

http://www.kirkhammotorsports.com

 

[itsmoked]

Yeah? I'll say this crazy scheme is there for one purpose. Marketing! It's to lock you into a strange Haas controller that makes it impossible to use anyone else's VFDs. I see these "better ideas" that are nothing more than customer traps all the time. I have worked for companies that struggled to put up these one-way doors. The "grand improvement" may actually be some tiny improvement over the 'common method' but often you are trading away all competition and eventually any access to 'new and improved' developments made by other companies. Improvements you can't switch to without prohibitive expenditures.

I certainly wouldn't go this route.

But to each his own.

And... Presently I'm listening to Beethoven - Symphony - No.5 Allegro Con Brio You know: DAH-DAH-DAH--Dahhhhh

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Keith;
Normally the power of a motor flat-lines when running above base speed.
If you can continue to increase the voltage to maintain the V/H ratio the power will increase above base speed. But you know that.
But, if you can't raise the voltage, how about dropping the voltage rating of the motor.
Example;
Motor rated at 230 volts.
Power maxes out at 230 volts/60 Hz.
Now connect in delta and drop the inverter output to 133 volts at 60Hz. The motor will draw more current but will produce the same power at the same speed. Now run the inverter up to 230V/104 Hz and 173% of base power. More power and speed out of the same motor.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Thanks Bill. I have that. But I would still ask why not use say a 130V motor with 240V safe wiring and OTS VFDs?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

There are situations where you want a high torque at low speeds and less torque when you get up in speed. That is especially true in many machine-tool applications.

Usually you use a gearbox for that. But if you try to shift gears while turning a circular surface, you will get nasty traces in that surface. I can imagine that some kind of a complicated clutch can do the shifting without stopping the lathe. But it sounds expensive and complicated.

If you want full torque and full speed out of a drive system, it has to be diesigned for maximum spedd times maximum torque. By using some kind of gear (my guess is winding switching in this case), you can have full torque at low speeds and full speed at low torques and still use a drive system that is, perhaps, one fourth of what you need if you design for "the whole square" so to say.



Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DKirkham]

Bill,

I always liked Bach more than Beethoven.



Thank you all for your responses!

David

http://www.kirkhammotorsports.com

 

[Skogsgurra]

Beethoven isn't baroque - is he? I thought more classisistic/romantic.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DKirkham]

Gunnar,

I is late and I am still awake

Gunnar hit the nail square on the head. The switch must be extremely smooth as gears introduce vibrations in the milling head and leave witness marks (traces) on the part that is being machined. Such marks can ruin a part (I am thinking of a custom steering rack and pinion I made only yesterday out of 300 Maraging steel.)

I am confident this works. Now, I ask the electric motor theory gods to answer the ultimate question...How? Why?

David

http://www.kirkhammotorsports.com

 

[Skogsgurra]

I think I answered that? To some extent, at least. A complete answer would mean one examines the equipment first. Guessing is a nice game, but doesn't produce answers.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DKirkham]

Gunnar,

Yes, you did!

I was dreaming more about "how" the actual electrons are moving in the wires and how this affects a given system...a question like you would ask your physics professor in class and drive all the other students crazy (who are only trying to memorize equations) as your professor delights in pontificating on the process.

I guess I should not drive the engineers on this site crazy with such ruminations.

Thank you all so very much! You have been a great help.

David

http://www.kirkhammotorsports.com

 

[cswilson]

This type of switching scheme is quite standard for high-speed spindles. There are even fancier schemes in the literature; I don't know if they are in common usage.

Let me see if I can amplify skogs' and waross' comments to make it clearer.

Very basic 3-phase AC circuit analysis:

For a Wye-connected load:

Vphase = (1/sqrt(3))*Vline
Iphase = Iline
For a Delta-connected load:

Vphase = Vline
Iphase = (1/sqrt(3))*Iline

So when you switch the motor from Wye to Delta, you bump up the voltage to the phase by a factor of 1.732, but reduce the current through the phase by the same factor.

The higher available phase voltage permits higher speeds, but the reduced phase current means less torque capability. As skogs says, this is equivalent to a change in mechanical gear ratio of this same factor. Delta connection provides a "higher gear".

As a possibly relevant aside, the prototype Tesla electric sports cars had a 2-speed gearbox. Unfortunately, these got ground up very quickly in endurance testing (my guess is that they were not up to handling full torque at zero speed, which a vector-controlled induction motor can provide, but an internal combustion engine cannot). The production version has a single-speed gearbox, and Tesla says it is now using electrical means to get the full torque/speed range. I wonder if they are pulling the Wye/Delta switch?

Curt Wilson
Delta Tau Data Systems