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…

 

[edison123]

Jeff, OP mentions 440 V motor, so the source is 440 V.

As long as the motor full load current is within the drive capability, I don't see any issue other than if the winding can withstand dv/dt of the drives. Many of our clients are switching over to ac drives with old windings and the winding failures are rare.

It's high time OP chipped in here with so many replies here.

 

[waross]

Jeff, OP mentions 440 V motor, so the source is 440 V.

Had the OP mentioned 460 Volts (standard motor voltage rating) rather than the very old 440 Volt rating, that would not change the 480 Volts standard North American Source voltage.

 

[edison123]

Whether the supply voltage is 440/460/480 V, the drive can be programmed to output 440 V to suit the motor.

 

[arianaa]

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

Using a 500 hp motor rated at 440 V with a 6-pulse drive rated at 600 A can lead to compatibility issues. The drive may not be able to provide the necessary voltage and current required by the motor, potentially causing inefficient operation or even damage. It's crucial to ensure that the drive and motor ratings match to avoid these problems.

 

[Gr8blu]

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

In the early days, there was just "pulsed DC" - which meant either half-wave or full-wave rectification of a 3-phase source. Full wave produced 6 pulses.
More modern drives may opt for a PWM approach, where a processor controls a specific silicon controlled rectifier wired in series with the motor winding. In this case, it can't really be called an "n pulse" drive, because the timing and width of the pulses varies considerably over the operating range.
There are even some drives out there using MOSFETs that have an H-bridge configuration, as well.