500 HP, 440V motor

[unclebob]

What happens if you try to use a 500 hp motor, rated at 440 V , with a 6-pulse drive, rated at 600 A?

 

[LittleInch]

 

[wayne440]

Claiming no expertise, I will guess that 600A is close to the FLC of that motor. To me, you do not have enough drive capacity.

 

[unclebob]

I would use, at a minimum, a 12-pulse drive.

 

[LittleInch]

If your motor wasn't designed for VFD, then you will have big problems apart from the very rough nature of a 6 pulse drive unit.

 

[waross]

Discounting the 6 pulse drive and considering any VFD:
As far as I know, 440 Volt rated motors haven't been made for over 50 years.
Expect early failure from the old, non-inverter rated, insulation.

 

[jraef]

The output voltage of a VFD can be tailored to be whatever the motor nameplate voltage is. So when you program the motor nameplate data into the drive as it being a 440V motor, the drive will (should) limit the voltage at full speed to 440V.

That said, the other concerns raised are very valid and concerning. 440V as a motor voltage has not been a standard for decades, long BEFORE the advent of VFDs and the associated voltage stresses they can impose on motor winding insulation. So it is HIGHLY UNLIKELY that this motor is designed to run from an inverter and will not be able to handle that. Making matters worse, the 600V source means that the individual pulses in the PWM output if the drive will be at the DC bus voltage of the 600VAC input, so 846VDC, instead of that of a 480V input, 677VDC. So the voltage stresses on the windings will be even worse.

I would give it a week to fail on winding insulation breakdown. You could if course add a Sine Wave Filter to the output of the VFD to mitigate that risk. It will likely cost you as much as a VFD.

 

[Gr8blu]

Hmm. I see a lot of assumptions being made here. The original post did not mention whether the machine was AC or DC - in which case a 440 V(dc) design could be fairly recent manufacture, for a very specific application and/or installation. Also - OP did not mention a nameplate current or speed: a typical three-phase AC machine would be drawing in the neighborhood of 580 A at 440 V; a comparable DC unit would draw around 890 A. A 600 A(ac) drive might have enough to run flat out ... a 600 A(dc) drive won't.

If it IS an older machine (AC or DC), the concern for winding damage from the electrical stresses occurring due to the drive output voltage waveform is valid. Additional thermal stress from the harmonics being produced in the drive output current waveform will also accelerate failure.

 

[jraef]

Hmm. I see a lot of assumptions being made here. The original post did not mention whether the machine was AC or DC - in which case a 440 V(dc) design could be fairly recent manufacture, for a very specific application and/or installation. Also - OP did not mention a nameplate current or speed: a typical three-phase AC machine would be drawing in the neighborhood of 580 A at 440 V; a comparable DC unit would draw around 890 A. A 600 A(ac) drive might have enough to run flat out ... a 600 A(dc) drive won't.

If it IS an older machine (AC or DC), the concern for winding damage from the electrical stresses occurring due to the drive output voltage waveform is valid. Additional thermal stress from the harmonics being produced in the drive output current waveform will also accelerate failure.

“6 pulse drive” is a clue that this is AC…