230V Nameplate motor, Running at 455V and 100Hz via VFD

[topgone]

Yes you can, as long as you increase the voltage at the same time. Think of HP as a shorthand notation of "A certain amount of torque at a certain speed". If you increase either value, you increase HP. The trick is to increase one without a corresponding decrease in the other. That's what happens when you MECHANICALLY change speeds, i.e. a gearbox or belt and pulley system. Speed goes up but torque goes down, or vice versa, but HP remains the same (other than added losses in the process). But with a VFD, torque is a product of voltage AND frequency, you can think of it as a V/Hz ratio. If you increase or decrease them together at the same ratio, you can change HP without changing torque. Lower is of course easy, that's what we are essentially seeing with the traditional application of a VFD. At 50% speed we are at 50% voltage, torque remains constant because the V/Hz ratio is unchanged, therefore HP is 50%. But at 100% speed and 100% voltage, you are maxed out. Since you can't make the VFD put out more than 100% voltage, any further increase in frequency begins a DECREASE in torque; we call this "operating in Constant HP mode" because with no additional voltage, you can no longer maintain the V/Hz ratio and torque begins to drop off.

I would like to ask for some more enlightenment on this portion. Please bear with me for a few moments.

You said: "HP as a shorthand notation of "A certain amount of torque at a certain speed"." . I have no problem with that. But when you said it is possible to operate the pump at a higher frequency and not increase the voltage, something seems not right. The OP specifically mentioned the VFD is capable of providing 400V @ 97Hz. Clearly, this VFD maxes out at that voltage and frequency, hence the need for us here to respond whether there will be no problems with him agreeing to the proposed setup - 230V motor-pump to be driven by a 400V-100Hz VFD, that is.

I must agree that your scenario is possible when a 230V VFD was in use and that the VFD capacity was maximum at 230 volts. Further incursion into higher frequency region becomes a constant power mode.

Still, my opinion is that in order for that setup to work, the owner should make sure the motor is rated for inverter duty and that necessary limits be punch-in into the VFD configuration that will protect the motor (VFD settings set to conform with motor capacity). If indeed, the owner want to take advantage of higher output or higher delivery head, I recommend the HP rating of the drive motor be checked and should be bigger than the capacity of the submersible pump else the motor gets toast! I also would like to point out that most motor suppliers to submersible pump makers learned how to over-rate their motors knowing that the motor duty will be that of being submerged under water. That could add to the problem here since we would expect that the motor actual rating will be smaller compared to the pump rating.

 

[T.M.Haja Sahib]

Still, my opinion is that in order for that setup to work, the owner should make sure the motor is rated for inverter duty and that necessary limits be punch-in into the VFD configuration that will protect the motor (VFD settings set to conform with motor capacity). If indeed, the owner want to take advantage of higher output or higher delivery head, I recommend the HP rating of the drive motor be checked and should be bigger than the capacity of the submersible pump else the motor gets toast! I also would like to point out that most motor suppliers to submersible pump makers learned how to over-rate their motors knowing that the motor duty will be that of being submerged under water. That could add to the problem here since we would expect that the motor actual rating will be smaller compared to the pump rating.

Yes.The motor size should be suitable for running the pump above the base speed.The original connection of motor in delta or star should not be changed for this purpose......

 

[Jraef]

I would like to ask for some more enlightenment on this portion. Please bear with me for a few moments.

You said: "HP as a shorthand notation of "A certain amount of torque at a certain speed"." . I have no problem with that. But when you said it is possible to operate the pump at a higher frequency and not increase the voltage, something seems not right. The OP specifically mentioned the VFD is capable of providing 400V @ 97Hz. Clearly, this VFD maxes out at that voltage and frequency, hence the need for us here to respond whether there will be no problems with him agreeing to the proposed setup - 230V motor-pump to be driven by a 400V-100Hz VFD, that is.

Sorry for not being clear enough.
First, as I mentioned, this can only relate to a DUAL VOLTAGE motor, i.e. 230/460 60Hz if it's a NEMA design, 230/400V 50Hz if it is an IEC design. If we go with the 400V as not being a typo or other error, that would suggest that this is am IEC motor. For those, the motor will be dual voltage, where you connect the motor INTERNAL windings in star (wye) for 400V and delta for 230V. So in his scenario, they are proposing using the delta connection inside of the motor, but applying the 400V to it from the VFD. So when connected for 230V (delta), the V/Hz ratio becomes 230 / 50 or 4.6:1 and if they run it up to 100Hz (2X normal speed), in order to maintain the proper V/Hz ratio the voltage will need to be 460V, not 400V. If they stop at 400V, then the maxim um speed could be 400/4.6 = 87Hz, not 97Hz. So that's why I said there is likely an error in the numbers somewhere. What I was addressing however was that this is a VERY common application of VFDs and motors for high speed applications, this is not in and of itself unusual.

I must agree that your scenario is possible when a 230V VFD was in use and that the VFD capacity was maximum at 230 volts. Further incursion into higher frequency region becomes a constant power mode.

No, you aren't following, again I apologize for not making it clear. In order to accomplish this, you CANNOT do it with a 230V drive, because you cannot apply more than 230V to a 230V drive. To do this, you must use a DUAL VOLTAGE motor strapped for the lower voltage, and a VFD and supply voltage that is at the higher voltage. That way as you increase the frequency above the base speed rating, you have more voltage to keep increasing with it and maintain the V/Hz ratio.

Still, my opinion is that in order for that setup to work, the owner should make sure the motor is rated for inverter duty and that necessary limits be punch-in into the VFD configuration that will protect the motor (VFD settings set to conform with motor capacity). If indeed, the owner want to take advantage of higher output or higher delivery head, I recommend the HP rating of the drive motor be checked and should be bigger than the capacity of the submersible pump else the motor gets toast! I also would like to point out that most motor suppliers to submersible pump makers learned how to over-rate their motors knowing that the motor duty will be that of being submerged under water. That could add to the problem here since we would expect that the motor actual rating will be smaller compared to the pump rating.

Agreed, the supplier would have to take responsibility for applying suitable products for this application. From the initial post, they told him "they do this all the time" which to me would imply that they know all these issues, but it never hurts to ask and make sure.

 

[topgone]

@jraef,
Thanks a lot for taking time to clear it up with the above post. Now it's crystal clear.