# VFD connection



## magmash (Jul 20, 2012)

Hi

I am sure this question have been asked before, but i am not able to find a thread about it using google .

How should a motor be wired to a VFD, In WYE or Delta configuration ?


I understand it like this. If the supply voltage is 230V then the motor should be wired Delta to the VFD if the motor states 230V for Delta, or if the supply Voltage is 380V it should go Wye to the VFD if motor states 380V for Wye.


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## JRaef (Mar 23, 2009)

Wye or Delta internal motor connections can ONLY be determined by the motor connection diagram, often on the motor nameplate or on a label on the inside of the connection box lid. There are multiple possibilities, so no generalities can be applied with any reasonable certainty.

Shorter version: RTFM


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## magmash (Jul 20, 2012)

JRaef said:


> Wye or Delta internal motor connections can ONLY be determined by the motor connection diagram, often on the motor nameplate or on a label on the inside of the connection box lid. There are multiple possibilities, so no generalities can be applied with any reasonable certainty.
> 
> Shorter version: RTFM


Shouldn't one wire the motor in a configuration so it matches its input voltage ?, I mean if the VFD is putting out 380V and the motor is rated for 380V in DELTA it should be wired in DELTA and not in WYE which lets assume is rated for 460V ?


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## AK_sparky (Aug 13, 2013)

Some motors have all the winding connections accessible so they can be configured wye or delta. The VFD doesn't care, but you have match the VFD output voltage to the motor configuration with the same voltage.


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## DriveGuru (Jul 29, 2012)

magmash said:


> Shouldn't one wire the motor in a configuration so it matches its input voltage ?, I mean if the VFD is putting out 380V and the motor is rated for 380V in DELTA it should be wired in DELTA and not in WYE which lets assume is rated for 460V ?


 There is more to take into consideration that just the motor voltage. Can we get a motor nameplate and the model drive you are using? You have to be careful with wye and delta connections, you can easily starve the motor for torque or overexcite the winding which is just as bad, both can let the magical smoke out of your motor.


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## Big John (May 23, 2010)

DriveGuru said:


> ...You have to be careful with wye and delta connections, you can easily starve the motor for torque or overexcite the winding which is just as bad, both can let the magical smoke out of your motor.


 Is that a fancy way of saying you'll under- or over-voltage the motor? 

I've never heard of motor winding configuration mattering beyond selecting the configuration for the applied voltage.


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## DriveGuru (Jul 29, 2012)

Big John said:


> Is that a fancy way of saying you'll under- or over-voltage the motor? I've never heard of motor winding configuration mattering beyond selecting the configuration for the applied voltage.


 Sorry I tend to think of things in terms of what it's actually doing to the motor, yes you can over and under voltage a motor. Once you introduce drives into the equation you now have to also consider the applied frequency. A 380v/50hz motor for example will not be very happy about having 60hz applied to it. Also in certain circumstances, it's possible to wire say a 230/460 motor for 230, and feed it 460v/120hz and essentially double its horsepower rating, I've done this on several fan dyno's. A drive introduces another dynamic, as opposed to fixed 50/60hz. It's all about the applied V/HZ ratio. With the proper drive configured properly, you can wire that motor either way, with no difference in performance.


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## Big John (May 23, 2010)

DriveGuru said:


> ...Also in certain circumstances, it's possible to wire say a 230/460 motor for 230, and feed it 460v/120hz and essentially double its horsepower rating, I've done this on several fan dyno's....


 Interesting, I've never seen that. What's the limit there, magnetic saturation? Why wouldn't it be in everyone's interest to drive a smaller motor at a higher frequency? It would reduce the cost of a lot of VFD installs.


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## Cow (Jan 16, 2008)

DriveGuru said:


> Also in certain circumstances, it's possible to wire say a 230/460 motor for 230, and feed it 460v/120hz and essentially double its horsepower rating, I've done this on several fan dyno's.


I've seen that on a 125HP air compressor once, makes a guy go:blink:. Seems like a weird way to go about running a motor.


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## ScooterMcGavin (Jan 24, 2011)

Big John said:


> Interesting, I've never seen that. What's the limit there, magnetic saturation? Why wouldn't it be in everyone's interest to drive a smaller motor at a higher frequency? It would reduce the cost of a lot of VFD installs.


The limit is voltage. Once you hit your 60hz at full voltage you cant increase voltage anymore so your v/hz ratio starts to drop and you begin to lose torque ( I think). By doing the 230 trick the you keep your v/hz ratio all the way up to 120hz @ 480v


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## DriveGuru (Jul 29, 2012)

Big John said:


> Interesting, I've never seen that. What's the limit there, magnetic saturation? Why wouldn't it be in everyone's interest to drive a smaller motor at a higher frequency? It would reduce the cost of a lot of VFD installs.


Limits are speed, torque curve, heat, mechanical limits, you are limited by the dynamics of the motor. You are not saving anything on the drive side, in the instance I gave an example of, the drive still needs to be sized at twice the horsepower rating. You can't get something for nothing. Otherwise perpetual motion would be possible


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## JRaef (Mar 23, 2009)

DriveGuru said:


> Limits are speed, torque curve, heat, mechanical limits, you are limited by the dynamics of the motor. You are not saving anything on the drive side, in the instance I gave an example of, the drive still needs to be sized at twice the horsepower rating. You can't get something for nothing. Otherwise perpetual motion would be possible


That's right. The only time it is done is when the required speed adjustment range needs to be wider than what you can get from 0-60Hz, often the case when the gear ratio is so low that running a motor at very low frequency might require too much external cooling to be cost effective.

Example: I once did a system for an ice maker OEM system in which the ice was formed on a rotating drum with refrigerant pumped through it and raked off. The drum had to turn extremely slow or the ice would not form. So they used a 450:1 gear box ratio and could run the motor faster, but that was the fixed speed version. When they wanted to offer adjustable speeds to change the thickness of the ice flakes, it meant going SLOWER at a 4:1 adjustment range and if I used a 4 pole motor at 1725 RPM, I would have to try to run it at less than 15RPM in some cases. So we did the doubling trick and changed to a 900:1 gear ratio, that way the VFD was running the motor from 30-120Hz (50-200% of base speed) all of the time, never so slow that it needed external cooling. So originally this had been a 1/4HP motor, so we had to put in a 1/2HP VFD, but no big deal on cost there. At 125HP however, it would be.


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## JRaef (Mar 23, 2009)

magmash said:


> Shouldn't one wire the motor in a configuration so it matches its input voltage ?, I mean if the VFD is putting out 380V and the motor is rated for 380V in DELTA it should be wired in DELTA and not in WYE which lets assume is rated for 460V ?


Yes, you must wire the motor to match the input voltage, of course. What I was saying is that you cannot ASSume in advance that this is going to be Wye or Delta, it depends on how THAT motor was designed to operate. For example if you want to run it at 380V, that is going to be a Wye pattern if the motor is designed as 220/380, but if the motor was designed as 380/690, then you would connect it in Delta for a 380 V supply. So again, go by what the MOTOR says it needs to have, not some ASSumed convention.

Don't know how 460V crept into this, but here's a little side note trick on that; if you have a 380V 50Hz motor, it is essentially the same V/Hz ratio as 460V 60Hz. Irrelevant when a VFD is involved really, but if not, do NOT run out and buy a 480-380V transformer as most people jump into doing, it will starve the motor for voltage at 60Hz operation and smoke it. Just feed it 480, it will be fine, although it will spin 20% faster. That higher speed will be a factor if it's a centrifugal pump or fan however, because the LOAD on the motor (power requirement) will increase at the cube of the speed increase, but the motor power only increases in a straight linear fashion. So be prepared to adjust flow to avoid overloading the motor (or use a VFD).


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