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.

 

[unclebob]

Adding more details here:

Motor has been tested and is in good shape. The drive however is burning parts on the control board: MOV, capacitors.... The newer drive installed 2 weeks ago is already showing signs of burning. Application is using 47 Hz, its not at full speed. I've been asked to install a power recorder to try to identify the problem.

Main power comes from a 550 to 440 V , 1000 KVA transformer. The 440 V side loads are 5 drives, so the secondary is infected by harmonics. Readings taken upstream of the faulty drive show 50% THD for currents and 5.3 % THD for voltages. Could harmonics created by other drives affect this one ?

Drive is a Parker. And the controller doesn't show any alarms at all.

 

[waross]

I am wondering about the source and history of a 440 Volt rated motor?

That aside, how about scoping the 440 Volt supply, the DC buss and the drive internal control voltage for signs of high voltage transients from harmonics?
Universal practice in North America is to run 460 Volt motors on 480 Volt supplies, I would have chosen a 460 Volt supply for 440 Volt rated motors.
The choice of 440 Volts suggests that the original designer was short of real world experience.
However, in North America 550 Volt supplies from utilities have not been seen for about half a century, more or less.
Your 550 Volt supply may be 600 Volts.
Or
This may be a very old plant with an original 550 Volt supply still in place,
But still;
It may be well to check the 440 Volt supply arrangement, particularly the grounding.
My favourite and often the most economical 550/440 V or 600/440 V transformation leaves 347 Volts to neutral/ground on one phase, rather than 277 Volts.
If the drive is inadvertently taking higher than normal line to neutral voltage for the control transformer, that may explain the board failures.
The solution is to "roll" the supply connections to the drive so that the internal transformer is supplied the expected voltage.
The higher voltage to neutral is only seen on one phase.

 

[edison123]

That's a lot of current THD.

Any reason to go for 440 V motors when the incoming source is already 550 V?

Rewind the motors to VFD duty 550 V with lower current handling and get rid of transformer, which is one more component to maintain and one more source of failure. Or use the transformer for other non-motor loads.

 

[Gr8blu]

@unclebob
To answer your question - multiple drives on a single bus absolutely affect each other in terms of harmonics.
Every drive creates harmonics on the upstream (bus) and downstream (load) side. These are both voltage and current harmonics, with the current harmonic amplitude (as a percentage) often being significantly higher than the voltage.
All drives are also (fairly) linear when it comes to doing their job. If the incoming power is clean, the downstream power output remains reasonably clean (within the harmonic performance of the drive). If, on the other hand, the incoming power is full of harmonics, it gets changed to whatever the downstream output is set to be - and includes all that upstream garbage.

 

[LittleInch]

So in fact it's actually got nothing to do with the motor, it's all about the drives going bang because of all the harmonics?

 

[LionelHutz]

A diode rectifier front end feeding a DC bus capacitor doesn't care at all about about current harmonics from other drives, it doesn't care much about voltage harmonics - 5% certainly won't affect it, and it at most passes a little residual noise from the input side to the load side.