Sometimes you can get that kind of motor behavior when the drive is set up as sensorless vector but the motor ID run has not been made or is defective. If the drive can be configured as a V/Hz drive, see if it will run the motor properly in that mode.
Are these motors running independent pumps or are the two pumps piped in parallel? If in parallel, are the VFD's running independently against independent setpoints or are the two VFD's linked together in some way? If linked, please describe how.
The old MG set motors will likely not be suitable for rectified unfiltered DC power without significant derating. The magnetics were designed for smooth generator DC and will overheat on DC with ripple on top.
The stress on power-up is largely a matter of managing the inrush current to the DC bus capacitors.
I would think that a properly-designed lightning suppression network ahead of the drive would be a better option that frequent power cycling. Whether the inrush current is limited by precharge...
Cycling input power on a VFD is very stressful to its power components and should be avoided whenever possible. Surely, cycling should be limited to not more frequent than once per hour.
A key piece of information is missing here. Is the incoming AC power balanced to ground, floating to ground, or deliberately offset to ground as in 120/208 or 460V corner-grounded delta.
Floating or unbalanced input power can cause the output side capacitance to charge up the DC bus. I've...
The capacitance between the phase leads or maybe between the leads and ground are likely different. At such long lead lengths, that can be the difference.
While haven't personnally done this, I believe that the addition of a 90VAC bucking autotransformer in the 480VAC supply lines would do the same thing = 380-400VAC at the motor.
jraef, first, thanks for the CB recommendations on the individual motor leads. I've always recommended a fused disconnect with overload relay but yours sound better and with only one device.
I'm curious why the dread about single phasing one of the motors.
An output short circuit fault with the motor leads disconnected is usually a shorted IGBT. They will generally short when they fail but, in your case, they didn't.
Sometimes, at a test voltage of 1.5V, the short will not appear where, at operating voltage of 660VDC, it will. That's probably...
Allen Bradley has promoted their "motor terminal protector" for many years but, while it may protect the motor adequately, it does nothing to quiet the motor leads.
As skogs says, a reactor or dv/dt filter mounted as close to the drive output terminals as possible is preferred.
jraef is correct. Most drives rated 480V are actually rated 380-500V when you read the fine print. And, no, you don't have to make any hardware changes and generally no software changes either.
But note his comments about the output voltage being limited to the input voltage. That pretty...
Assuming the motor will be in a constant hp range from 50 to 73.3Hz, then the hp throughout that range will be equal to the hp at 50hz.
The hp at 50hz will be 50/60 of the nameplate hp at 60hz assuming you program the drive for constant V/hz ratio from 0 to 50hz equal to 480/60=8.00. Then...
