wye - Delta -> differences and stereotypes

[Punx0r]

I don't know if it helps, but there's some info here
https://endless-sphere.com/forums/viewtopic.php?f=28&t=15344#p254773
about overlapping poles not working in delta very well; perhaps this is part of that "optimization" for wye?

Good link If nothing else it high-lights the variable of how some motors use overlapping winds and shared poles and others do not.

A quick google for "delta circulating currents" also brings up some illuminating information on why this occurs and the significance of the 3rd order harmonic.

Regarding some of the other points, I've not seen (or heard of) an industrial 3 phase induction motor with hall sensors (or similar feedback) but doesn't mean they don't exist. Uncommon/non-standard usually indicates something is an exception to rules of good practice. Same with caps on a 3 phase motor. Start & run caps on a single phase machine make sense as the phase difference produces a rotating magnetic field - something you get automatically on a poly-phase machine.

Basic theory, rules of thumb and standard practice are usually suitable to provide a first-order indication of whether an idea is good or not. Then delve deeper into the technical details if it looks promising, or the potential rewards are so great it's worth chasing even though it's unlikely to subsequently turn out to be good.

In this case, the starting claim is "significant performance gains between wye & delta"

First order assessment: Basic theory says same motor/windings/iron = same performance for both
Second order assessment: Actually, there are circulating currents in delta, so potentially there is a difference
Third order assessment: Actually, this depends on the specific motor construction and ranges from a small difference in efficiency to unusuable
Fourth order(?): Check out specific motor designs to see what difference there is.

Each steps takes more time/money/effort and narrows the potential benefit and my personal preference is to filter out a lot of ideas at the first step. There is a chance of missing one that's actually good, but it saves a lot of time (which can be spent productively developing other ideas).

 

[ElectricGod]

I don't know if it helps, but there's some info here
https://endless-sphere.com/forums/viewtopic.php?f=28&t=15344#p254773
about overlapping poles not working in delta very well; perhaps this is part of that "optimization" for wye?

Good link If nothing else it high-lights the variable of how some motors use overlapping winds and shared poles and others do not.

A quick google for "delta circulating currents" also brings up some illuminating information on why this occurs and the significance of the 3rd order harmonic.

Regarding some of the other points, I've not seen (or heard of) an industrial 3 phase induction motor with hall sensors (or similar feedback) but doesn't mean they don't exist. Uncommon/non-standard usually indicates something is an exception to rules of good practice. Same with caps on a 3 phase motor. Start & run caps on a single phase machine make sense as the phase difference produces a rotating magnetic field - something you get automatically on a poly-phase machine.

Basic theory, rules of thumb and standard practice are usually suitable to provide a first-order indication of whether an idea is good or not. Then delve deeper into the technical details if it looks promising, or the potential rewards are so great it's worth chasing even though it's unlikely to subsequently turn out to be good.

In this case, the starting claim is "significant performance gains between wye & delta"

First order assessment: Basic theory says same motor/windings/iron = same performance for both
Second order assessment: Actually, there are circulating currents in delta, so potentially there is a difference
Third order assessment: Actually, this depends on the specific motor construction and ranges from a small difference in efficiency to unusuable
Fourth order(?): Check out specific motor designs to see what difference there is.

Each steps takes more time/money/effort and narrows the potential benefit and my personal preference is to filter out a lot of ideas at the first step. There is a chance of missing one that's actually good, but it saves a lot of time (which can be spent productively developing other ideas).

I like your 4 orders of assessment. In the case of wye/delta switching it definitely passed number 1. The theory was good and actually trying it out initially worked out too.

I do have a question for you. You posted some thing much earlier in this thread and then just now too. I didn't respond to it the first time since I thought it wasn't applicable to wye/delta switching.

Two motors, one wye and one delta wound for the same Kv should use the same amount of current and develop the same amount of torque. That's assuming all else is equal in the two motors.

Let's ignore the circulating currents, back EMF or other issues involved with how a motor may or may not be optimized for wye or delta. In my experiments it is the same motor all the way through running at 2 different Kv's so it seems to me that the above statement isn't applicable. The Kv is 1.7X more in delta than it is in WYE. The winding's are the same, but how they are connected together in the same motor is very different. I would think that changed quite a few things such as the fact that in WYE two phases are in series, but in delta they are in parallel with the third phase. All of a sudden the motor on the same voltage has a higher top RPM and probably wouldn't consume current the same as it did in WYE. I'm pretty sure I've read this in several places that people reported that their motors used more current in delta than they did in WYE. Is that due to the significantly increased KV in the same motor or 100% because the motor was optimized for WYE? It seems to me that significant change in KV would effect current draw all by itself.

 

[ElectricGod]

I don't know if it helps, but there's some info here
https://endless-sphere.com/forums/viewtopic.php?f=28&t=15344#p254773
about overlapping poles not working in delta very well; perhaps this is part of that "optimization" for wye?

Thanks for posting this other thread. Lots of good stuff in there and then the article at the end is good stuff too.

 

[toolman2]

If the motor was built to be optimized in Wye, it will run like crap in Delta and make lots of heat. (No matter where your halls are timed)

If the motor was designed to be optimized in Delta, terminating it in Wye will result in poor performance. (No matter where your halls are timed)

If a Delta/wye switch works well for your motor, then your motor is unoptimized rubbish (like most Ebike and hobby grade motors).

Thanks Luke...

You confirmed everything I am seeing and why. Thanks so much for your input and for confirming that hall placement wasn't the issue. That's what I thought despite people saying otherwise. Now I would say this thread has served it's purpose. I unwittingly proved that a motor that runs well in WYE is crap in delta. I also feel exonerated that physical hall placement if correct is always correct wye or delta. It was suggested that hall/phase combinations changed when you switch from wye to delta. I think that is also false if the phase ends are connected correctly. In my case, with or without the relay in place, I saw the exact same behavior (3X more current draw in delta) with the same hall setup as WYE or in trying to find a "better" combination. It didn't make a difference. IE: reordering the halls for delta was not the issue. People who have experienced the need to reorder their halls when they switch from WYE to delta have had to do so because their phase ends were not connected correctly. I did not have this issue. My motor as seen in my wye/delta videos ran with the same hall combination before and after the switch over. I already had the optimal hall/phase combination.

This is one of those times where Luke swoops in...red cape flapping in the wind behind him while singing in a baritone voice "Here I come to save the day!!!"

Not sure why no-one has chimed in to correct the record on this, 5 or so years back here it seemed like common knowledge: Shifting from wye to delta (and vice versa) gives you a 30deg phase shift in timing, on every PM motor (and also transformers i believe).

The halls can only be in the correct position for one of these, it will then be wrong by 30deg for the other, and the halls being centered in between teeth is often the right spot but never a guarantee of correct placement.
Any no load draw testing will be massively influenced by hall timing so without correcting this first it would be difficult to conclude anything useful.

 

[Altair]

Electricgod, you made an error in your second post of this thread, in this phrase:
"So for this explanation, lets pretend you are using a single strand of 14 awg wire on this hypothetical motor. You wind each stator tooth with 10 turns and that gets you 200 Kv in WYE and 340 Kv in delta. Now you rewind the motor with 14 awg wire, but do 12 turns per stator tooth and now you get 240 Kv in WYE and 408 Kv in delta."

The Kv will be LOWER with more turns.
However, your subsequent explanations are correct on this particularity of motor winding.

 

[ElectricGod]

Electricgod, you made an error in your second post of this thread, in this phrase:
"So for this explanation, lets pretend you are using a single strand of 14 awg wire on this hypothetical motor. You wind each stator tooth with 10 turns and that gets you 200 Kv in WYE and 340 Kv in delta. Now you rewind the motor with 14 awg wire, but do 12 turns per stator tooth and now you get 240 Kv in WYE and 408 Kv in delta."

The Kv will be LOWER with more turns.
However, your subsequent explanations are correct on this particularity of motor winding.

Yup...totally did that backwards...lol. Dumb mistake. I knew better.

 

[liveforphysics]

Getting hall timing right is still critical, has a major effect on motor heating, and some motor designs will shift neutral timing location when delta-wye termination change is made.

I was merely saying, if the motor was designed for Delta and you Wye terminate it (or visa-versa), it doesn't matter so much that you can correct the hall timing if the motors BEMF waveform is compromised terribly (as it would be in an optimized motor).

I agree getting the halls in the right places is important, but there's no difference wye or delta for that hall placement.

How does one "optimize a motor" for WYE or delta? Please give me some articles to read on this subject.

Thanks

A motor is optimized by simulating various stator tooth geometrys with varous available magnet shapes on the rotor until the simulated BEMF appears as close to sinus as possible >99% is possible. The second part of optimization just removing the excessive back iron that isn't swinging in flux uniformly.

 

[Ianhill]

This is only my experiments and what I've been reading, The stator tooth area guides the field lines and depending on what power levels the motor is designed to handle and magnetic gauss of rotor etc the width of these teeth is critical, When putting to much current through the motors coils it's the tooth tip areas saturation that has the most effect, the stator laminations have no more area for magnetic gain its at its magnetized peak it's area is saturated the tooth tip needs more width, total lamination area.

Adding a higher voltage/larger peak to peak wave to the Inductior/coil in a motor then it's going to spin faster as we spin the motor faster the coils will reach a point at higher frequencys where the larger the inductance/more copper on each phase, the more it is going to limit the current, its the reverse of low speed high current saturation, at high speeds the magnetic field is not fully building and a switch happens first, because it's switching frequency is becoming to fast any load applied here will drop the rpm back down there's no torque to hold a load.

I think this is why my stock boma motor overheated at slow speeds on lower voltages, It's inductance was high and kv low so the stock controller didnt have the power to get full torque or the volts to get it out of its inefficent area so it stayed at low speeds, the wave form being slower had greater heating effect, but now with over double the total power, 1/3rd more volts and nearly double the amps its not getting so hot at full speed, So I think the chinesse put more copper in than needed in poor formation and run the motor from a controller to weak and the lead acids helped to give the voltage drop needed to slow the wave form to a point it's heating the motor with the pulses being too long a duration it's not using the motors full torque or is theres enough volts to get the pulses shorter.

If I'm wrong anywhere please feel free to correct me the more i learn the better. Just trying to work out how I can run a 1600w motor at 3.7kw and it's cooler at full speed and with constant stop starting.

Stock was 48v lead acid 33 amp, and now it's 60v 16s lipo and 58 amps took many a thumping and loves it was screaming up my road today like a angry dremil.

 

[Ianhill]

I think this is why my stock boma motor overheated at slow speeds on lower voltages, It's inductance was high and kv low so the stock controller didnt have the power to get full torque or the volts to get it out of its inefficent area so it stayed at low speeds, the wave form being slower had greater heating effect,

I must stop posting crap when I'm tired, the inductance is too low for the controller not enough chooching too get the full motion, and the new controller has better switching efficency so it had better control over the waveform proberly less current ripple etc, but without an oscilloscope and a brain I'll never know.

 

[jonnyc1986]

https://drive.google.com/file/d/10DRu0bGx2FkDbA7fYXo27U-48TqcDiol/view?usp=share_link

I registered for this forum SPECIFICALLY to throw in my 2 cents on a 6 year old dead thread. Apparently I enjoy screaming into the void. Okay, I wanted to add a few finer points to the difference between Delta and Wye with special consideration to how they are switched using a 3 phase bridge. If you take a look at my shitty picture I tried to show:
1. the phase sequence (not including FOC, just basic) is equivalent between Delta and Wye
2. Delta the phases are in parallel and Wye phases are in series (impedance in Wye is twice as high as Delta for the same battery voltage. So current is half(ish) that of Delta for the same battery voltage)
3. For Delta, for steps where only 1 low side Mosfet is on, that low side Mosfet will be passing twice the current due to two phases being in parallel.
4. Since the above is true, there will be a higher torque ripple for Delta connected motors.

So if you think in terms of the maximum amount of current a Mosfet will possibly have to pass running a Wye connected motor at a given voltage... the low side Mosfets running a Delta connected motor will have to pass 4 TIMES AS MUCH. VERY unbalanced switch loading.
To speak on the 1.7 times as much current instead of 2, it hasn't jumped out at me, if you want to tell me, I will happily learn. Possibly Wye coils being in series and sharing the same current for its inductor amp turns works out so its more efficient by %30. But if that were the case... wouldn't you be able to reduce the amount of turns in the Wye motor by half and get the same top speed as the Delta with a power savings of %30????? (and the equal mosfet loading and less torque ripple for free??)