# Wye connected motor on VFD?



## micromind (Aug 11, 2007)

If the motor is designed to be started on Y and run on ∆, it'll produce roughly 1/3 of its rated HP on the Y connection. 

Since this is a large motor, look at the nameplate and connection diagram carefully. Some large motors are designed to operate on Y at 460 volts 60HZ. 

If it is indeed designed for Y start and ∆ run, and it is connected Y, most likely it never got up to speed and therefore drew more current than it could handle. 

If it's a Y start ∆ run, it needs to be connected ∆ for a VFD. 

I've seen more than a few of these motors connected Y because the power system is a Y. The motor does not care what the power system connection is, it cares only what the phase-to-phase voltage is. 

If the motor is Y start ∆ run and it's connected Y, the proper voltage to run it would be 796. This is why when 480 is applied, it'll start with less torque and lower current.


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## John Valdes (May 17, 2007)

Blaren said:


> We have a 500hp motor on a VFD. The construction crew left the motor wired wye instead of delta and the motor started shutting down on over temp after running for almost a week.
> what would be the cause of this overtemp? I can't figure out if it is from the lower "ratings" in wye or the setup/functionality of a drive that has a wye connected motor attached?
> 
> thanks for any help!


You are lucky this motor survived this. I had this happen to a customer of mine. He went through two 60 HP vertical pump motors until we went out there to see what was wrong.
It was hooked up in the wye config. DOL start.
The VFD is what saved your motor. Had it been a line connection you would be looking for a new motor.

Everything Rob posted above is correct and should answer all your questions.


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## frenchelectrican (Mar 15, 2007)

Blaren said:


> We have a 500hp motor on a VFD. The construction crew left the motor wired wye instead of delta and the motor started shutting down on over temp after running for almost a week.
> what would be the cause of this overtemp? I can't figure out if it is from the lower "ratings" in wye or the setup/functionality of a drive that has a wye connected motor attached?
> 
> thanks for any help!


Those guys posted the correct info on them.

I will add this part .,, the motor dont care what supply system it is feeding to the motor.

The moot point is you check the name plate for proper connection.

500 HP is pretty big motor for some peoples but for me that is a run of mill size.,

did you or your crew verify the connection at the peckerhead to confirm if it is on straight delta connection ( this is a common way to hook up to VSD ) 

If you did have Wye - Delta system on the motor you will have to reconferation to straight Delta. 

Check the supply voltage to make sure it do meet the VSD requirement espcally if you are running on 480 or 600 volt system. once you verify it then check the VSD parmaiter to make sure it match the motor specs on nameplate.

again please check the connection at the peckerhead to make sure it is correct. this part is kinda semi common mistake when some peoples hook up the Y-D motor in wye setting.

This topic is simauir what we did talk sometime back not too long ago.


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## micromind (Aug 11, 2007)

The current curve of just about every motor is such that it draws a lot of current, way more than full-load, from a standstill until it's pretty close to full speed. 

This current is generally about 6X the full-load current. 

With a Y-∆ motor connected Y, it'll be around 2X. 

In your case, if the motor never reached the speed the VFD wanted, it'd continue to draw up to 2X its full-load current, less as it got closer to the commanded speed. 

The VFD will maintain close to the proper V/HZ ratio based of the speed feedback it gets but it'll pour as many amps to the motor as it is allowed to in order to increase the speed.


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## frenchelectrican (Mar 15, 2007)

micromind said:


> The current curve of just about every motor is such that it draws a lot of current, way more than full-load, from a standstill until it's pretty close to full speed.
> 
> This current is generally about 6X the full-load current.
> 
> ...


That is true Micromind.,

but the issue with OP's part I do not know what speed they did set for that motor so I am assuming if they ran lower than nameplate speed it can get overheated especially under 50% of base speed.. 

second thing I do not know if they did have very high intera load that can play other factor in there. 

But I am feeling that something is missing in there. 

The OP did not mention what type of VSD is there and how they got it setting currentally., ( beside a goof of wye connection instead of delta connection at peckerhead ) 

Most 500 HP motors I ran into typically have either 3 or 6 or 9 but some case 12 if Y-D set up. but first three is most common I know. ( for single speed set up )


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## paulengr (Oct 8, 2017)

Aside from 6 or 12 lead motors with access to both ends of the coils for wye/delta starters as mentioned the motor doesn’t care what feeds it and vice versa the drive doesn’t care if the motor is wye or delta. All that matters is that the proper voltage is set up on each one.

I ran into a warehouse operation in Florida not too long ago that purposely used the low voltage (230) configuration on a VFD then set the VFD up so the base speed was 120 Hz and nameplate voltage 460 V. This effectively fooled the VFD into running V/Hetz mode with twice the speed and double the correct voltage which roughly doubled the current. Fortunately the cool down time is long so this screwy setup “works” even though it’s obviously pushing more torque out of the motor than design.


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## Mike_kilroy (Sep 2, 2016)

paulengr said:


> Aside from 6 or 12 lead motors with access to both ends of the coils for wye/delta starters as mentioned the motor doesn’t care what feeds it and vice versa the drive doesn’t care if the motor is wye or delta. All that matters is that the proper voltage is set up on each one.
> 
> I ran into a warehouse operation in Florida not too long ago that purposely used the low voltage (230) configuration on a VFD then set the VFD up so the base speed was 120 Hz and nameplate voltage 460 V. This effectively fooled the VFD into running V/Hetz mode with twice the speed and double the correct voltage which roughly doubled the current. Fortunately the cool down time is long so this screwy setup “works” even though it’s obviously pushing more torque out of the motor than design.
> 
> ...


No fooling vfd here. Simply letting SAME v/hz curve continue to 2x base speed. Current did NOT increase at all: it will be same all the way up. Unless of course the load increased. And last, the torque output did NOT increase: it remained the same nameplate rating, just like the current. The motor HP became double at 480v speed, and as long as the motor bearings are good for 2x speed it can run forever at that rated torque, 2x HP, and 2x speed. No extra motor heating doing this.

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## paulengr (Oct 8, 2017)

Mike_kilroy said:


> No fooling vfd here. Simply letting SAME v/hz curve continue to 2x base speed. Current did NOT increase at all: it will be same all the way up. Unless of course the load increased. And last, the torque output did NOT increase: it remained the same nameplate rating, just like the current. The motor HP became double at 480v speed, and as long as the motor bearings are good for 2x speed it can run forever at that rated torque, 2x HP, and 2x speed. No extra motor heating doing this.
> 
> Sent from my SM-G900V using Tapatalk


So let me see here. We are at double the horsepower with the same current and same torque but double the speed, with NO thermal penalty? Not quite.

HP = Torque x Speed / 5252

That's just basic mechanics in that formula and clearly if we don't change torque but we do change the speed, then the horsepower has to change by the same amount. In this case 2X speed and 2X HP.

But working back from the electrical side we get:

HP = Input Power x efficiency x 0.746

So if the horsepower now doubles then something has to give and that means that the input power now doubles. Although I've WIRED the motor for half the voltage I'm now driving it at twice it's rated voltage. So correct that current does not change from name plate because we have:

V * I *1.732 * PF = Power

And with a drive PF is roughly 1.0 and at the motor it gets pretty close to that when we're running at 100% of name plate.

BUT getting back to that first number....HP = power x efficiency, efficiency has not changed. We now have twice the power going through that motor so we have twice the thermal heat in losses because efficiency hasn't somehow doubled as well. So we CANNOT operate at that point continuously. By NEMA standard MG-1 we can operate there for about 2 minutes without damage.


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## Mike_kilroy (Sep 2, 2016)

paulengr said:


> So let me see here. We are at double the horsepower with the same current and same torque but double the speed, with NO thermal penalty? Not quite.
> 
> HP = Torque x Speed / 5252
> 
> ...


Glad we clarified that the torque does NOT double.

Sure there is some more losses since efficiency did not change but now we put 2x volts @ same current into the system. But, but, but...

What motor do you have that does not have a fan of some kind on it? What does the airflow do when you doubled the speed? It went up by the CUBE of the speed, so it is actually not double but rather 9 times more cooling! 

No wonder the motor you saw did not fry itself! It is tickled pink to run that way!

PS: We have literally over 1,000pc 30hp motors wired at 230v running to 460 to make them 60HP spindles. Since 1978. All still happily running and our customers cutting metal sometimes 24/7 at 110, 120% on the load meter (OVER 60hp). These are GE and Reliance motors. Pretty Generic models. But don't feel bad - MOST people will say it is not possible, will overheat the motor, burn it out, etc. EVEN about 70% of the sales engineers for those motor manufacturers!


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## paulengr (Oct 8, 2017)

Ok so I’ll bite that the fan cooling is drastically improved. That certainly helps the stator. We can always increase stator cooling with more heat fins (surface area) or with a better fan if the pesky DOE folks keep their noses out.

But what about the rotor? That’s always the problem anyway...very poor heat transfer across the air gap and the reason that starts per hour for instance is so limited.


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## Mike_kilroy (Sep 2, 2016)

Yes, it is hard to get rotor heat out thru all the stator mass and airgap, but it is not a major portion of the limiting heat (losses) in an induction machine:

What are the various losses in an induction motor?
(See also Energy savings) Full load motor efficiency varies from about 85% to 97%, related motor losses being broken down roughly as follows:
Friction and windage, 5% – 15%
Iron or core losses, 15% – 25%
Stator losses, 25% – 40%
Rotor losses, 15% – 25%
Stray load losses, 10% – 20%.
Induction motor - Wikipedia
https://en.wikipedia.org/wiki/Induction_motor

The majority is I^2R heat losss due to current in the stator - ok, and smaller degree in rotor. As you know, the stator current is identical since we keep the v/hz curve the same, so NO additional losses there. So rotor losses remain the same also.

OK, your rotor:
Why core loss in 3 phase induction motor is neglected?
Usually we operate motor at slip in the range 0.04 ~ 0.06, thus for a stator frequency of 50 Hz , rotor frequncy is around 2~3 Hz. As core losses are proportional to square of frequency(Eddy current losses) or proportional to frequency( Hysteresis losses) , therefore the value of the Core loss is negligible for rotor.

So forget a lot more core losses.

You can see by keeping the current the same, just increasing the voltage did not generate a lot of additional heat to dissipate. Your friend's motor running to 120hz @ 2x base volts will be fine.

Induction machines are not simple linear devices and sorta hard to understand all the different interactions. Just accept that you can run any motor on its v/hz line higher in voltage without major impact - as long as the load and the motor mechanics are ok with the higher speeds. Studying the ins and outs of AC machines is a life long project - I know!


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## varmit (Apr 19, 2009)

This makes perfect sense, even though I had never thought about it. As long as the volt/hertz ratio is correct, everything should work fine. The limiters would be the mechanical speed limitations of the motor and mechanical drive components. You would also need to calculate the speed of the outer circumference of the driven load to avoid going supersonic, as in a large fan.


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## JRaef (Mar 23, 2009)

So back to the OP's issue, I have to inject a bit of clarity; the motor left connected in Wye will actually NOT run slower in terms of the BASE speed, because you have not changed the number of poles and the frequency getting to the motor will be the same regardless of the internal connection. S(rpm) = f/p where S = Synchronous speed, f= frequency, p = # of poles. Nothing changes there.

But what DOES change drastically is the amount of TORQUE the motor is capable of. A motor that was designed for Delta and connected in Wye will be getting 58% of its design voltage, and the torque will be the square of the voltage change. So 58%^2 = .333, which is the 1/3 value micromind stated earlier. 

If however the _*LOAD does not require more than 1/3 of the motor's available torque*_, the speed it spins will in fact not appear abnormal. But the _moment _you apply a load, the lack of torque will increase the slip and the motor will draw more current in the attempt to get back to normal slip speed, but because of the low voltage, that torque is not available. So depending on the amount of load, the SLIP SPEED will end up lower. I have had rock crushers misconnected like this and they ran for weeks before anyone noticed, because the operators would see the current increase and just back off on the infeed, meaning the motors were not loaded to what they were capable of. The call came to me because the OWNERS were complaining to the crusher mfr (my customer) that the performance was poor. I went out and discovered the misconnection of the motor. Had I not done that, it may have gone on like that forever.**

In the case of the VFD added into the mix, what happens is that the VFD will likely go into current limit to protect ITSELF as the current increases with slip, so the VFD was probably backing off on the speed, but still allowing the motor to draw more than rated current for a lengthy period. Because of the reduced speed and thereby reduced cooling fan effect at the higher current, the Over Temperature switch in the motor likely acted before the Over Load function in the drive did. So as mentioned, the VFD likely saved your motor for you.

**Side note: these were WEG motors from Brazil, where they do in fact use 762V for trailing mining equipment, so the motors were 762/440V rated. But the guys connecting the motors in the field didn't know any of this because WEG's nameplate just said "High / Low" connection patterns and they were used to connecting to the HIGH voltage pattern on 460V motors, meaning they were connecting them in Wye when they should have been Delta.


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## Mike_kilroy (Sep 2, 2016)

Thanks Jraef for clarification on OP delta vs wye; After addressing the other misconceptions brought up, I was going to write:

"With motor connected in Wye -- The inverter output would need to 1.73 voltage (460*1.73 = 796v) to produce rated torque (and power) at rated current.

So if they wanted to keep the Wye configuration they should set the VFD to 120/1.73= 69hz for 460v max output"

but didn't want to confuse people, so did not.


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## Oceanobob (Aug 14, 2021)

I read alot on this forum, and I just joined .... I see this last post was 2+ yrs ago, hoping I can add since my inquiry is directly related.

I have to hookup quite a few machines with motors that are 6 lead, with nameplate: 5.5 kw (7.5 hp), 220V, 60hz, 21.6A, 1170rpm, mfg by Jangsu in around 2014. 
These were previously operated with a Delta VSD/VFD on a 208 three phase system. I would like to run these on a 480 three phase system with a 10 HP Rockwell ABradley VSD/VFD.

Ergo: 220 motor connected to 480 VFD.

I much appreciate the information that the type of power system and the type of hookup to the motor are separate topics.

Alas: 
I did not gather from post number 10 how the motors (for those spindles) were connected, but I am thinking in my situation since the voltage is no longer at 220 and the VFD is connected to 480, should I connect using a wye? 
And yes I plan on operating these motors at [a self imposed limit of] around 1400 rpm.

With kind regards and thanks.


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## micromind (Aug 11, 2007)

A 220 volt motor connected ∆ would want to see 380 volts when it's connected Y. 

One way is to program the VFD to output 440 volts at 120 HZ then limit the HZ to 60, you'll have 220 volts at 60HZ going to the motor.


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## Oceanobob (Aug 14, 2021)

Will keep motor in the delta and adjust the VFD as recommended
Thanks!


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