60 Hz motor in 50 Hz, half speed operation with VFD

[edison123]

My client is importing an used, 460 V, 250 HP, 1750 RPM motor from US and intends to use it with a 415 V, 50 Hz supply at half the speed of 875 RPM with a VFD. The VFD will be rated for 125 HP due to cost reasons.

How should he program the motor details in his VFD ? 460 V, 60 Hz or 415 V, 50 Hz ?

How should he set the desired speed in each case ?



* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[LionelHutz]

Set the drive so the motor has a V/Hz ratio of 7.67. So, he could use put the motor settings into the VFD of 460V 60Hz or 415V 54Hz or 230V 30hz any other combination that creates the correct ratio.

Then, he has to set the maximum allowed frequency to 30hz.

 

[edison123]

Thanks Lionel. My thoughts exactly. Will the auto-tune function of the drive pose a problem if you input any of these inputs ?

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[DickDV]

Enter the motor nameplate data into the drive exactly as it is on the nameplate. Then set the max speed for any speed up to a max of 1480rpm. Above that speed the motor will starve for voltage.

If all you want is 875rpm and 125hp, I think the motor is an overly expensive choice for the application.

 

[jraef]

Assuming you (and he) know that the load HP requirement is commensurate with what you will be able to deliver at that speed, plus the lack of needing any extra accelerating torque, I see no problem with this. But use the recommended settings.

 

[edison123]

Thanks DickDV and jraef

The motor is package of vertical turning center, of which the client has many. They are all running at around 125 to 150 RPM at around 60 to 75 HP.

This used machine has an inbuilt gear box outputting 370 RPM at 60 Hz. Hence, the motor speed reduction to half to get around 150 RPM at 50 Hz.

With 50% output reduction due to reduced speed, the client still has a margin of 50 hp to play around.

So, to understand all of you, it doesn't matter which set of data we input (460/60, 415/54, 230/30), right ?

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[LionelHutz]

I was thinking about this more and the frequency you enter for the motor data is typically the point where the VFD stops maintaining the V/Hz ratio and switches to a constant voltage output. In other words, the motor goes from constant torque to constant hp. So, all will work but if you do chose 230/30 then you will not want to run the motor over 30hz.

My initial thought was that since you wanted to run a 250hp at 125hp that you wouldn't want to go over 30hz anyways but that may not be true.