Lenze L Force MD/MH motors...inverter connection question

Getting back into the controls field after a long hiatus going to school. Due to unforeseen circumstances I have been suddenly placed into commissioning a machine someone else designed, which I have no experience with.

Basically I am connecting several Lenze L Force MD/MH motor to PF755 drives using CIP motion. The drives are powered by 460VAC/60Hz. I wasn't previously familiar with the 87hz technique but quickly am. My question is: these AC motors have on the data plate specifications for 400wye/230delta, at 50hz, 460wye/265delta at 60Hz and 87Hz at 400V as well as being specified as an "inverter duty motor". According to the data sheet:

"MD/MH three-phase AC motors are designed for operation
on a fixed mains and for inverter operation.
For operation at 50 Hz, the motors should be operated in a
Δconnection at 230 V or in a star connection at 400 V.
For inverter operation, the base frequency has been set at
87 Hz at a rated voltage of 400 V in a Δconnection."

According to the supplier I should still be setting the motor windings to a Wye configuration despite using the PowerFlex drive. He states that the 87Hz is only needed for constant torque applications, whereas the hoisting application we are using it for doesn't. Other engineers in my office have verified his statement. Is the inverter connection mentioned in the Lenze data sheet only for an inverter connected to a 230-50/265-60 volt mains?

First, every hoisting application I've seen is or should be a constant torque device. That means that you will need a constant V/Hz ratio regardless of which way the motor is connected.

If your power train is already specified, then you have determined what the maximum speed must be for the motor. That will fix the maximum frequency that you can use.

You can see from the motor nameplate data that the motor in wye configuration needs a V/Hz ratio of 8 (480/60, 400/50). In delta, the motor requires a ratio of 4.6 (400/87, 265/60, 230,50).

So, you can go either way here. The difference is the max frequency and the available torque. In wye the torque is less but it is constant up to 87hz. In delta, the torque is greater but only holds constant to 60hz. The choice is determined by the reduction ratio of the drive train and the torque required on the winding drum. The hp ends up being the same at 60hz delta and 87hz wye.

Hi Dick,

Thanks for the answers but your ending examples have left me a bit more confused.
"In delta, the motor requires a ratio of 4.6 (400/87, 265/60, 230,50)."
"In delta, the torque is greater but only holds constant to 60hz."

So if I wanted 87Hz using Delta the motor drive requires a 400V mains and has a 4.6 (400/87) ratio but wouldn't have the constant torque the 265/60 or 230,50 would have.

"The hp ends up being the same at 60hz delta and 87hz wye."
How does one drive the motor to 87Hz in a wye configuration if 480V only gives 60Hz for the ratio of 8?

Since, in wye the base frequency is 87hz and in delta the base frequency is 60hz and the nameplate hp is the same at both points, solving the hp formula (hp=TxR/5250) for torque at both frequencies, you can see that the torque is lower on the 87hz configuration. With a constant V/Hz ratio below the base frequencies, you will have available from the motor the base frequency torque down to nearly zero speed.

Just one other curious observation: Since the motor clearly has insulation rated for 480VAC, in the delta configuration I wouldn't have to stop at 400V at 87hz. I could continue up to 480V at 104hz. At this point, since I have maintained the V/Hz ratio constant, the torque would also be constant up to 104hz and the hp would be 104/87 x the nameplate hp or, more hp than the nameplate value.

This is a common European trick to get more hp out of a motor than it is nameplated for.