Yes, the peak torque produced by the motor would be the square of the voltage difference. So the motor would be producing only 33% of it's rated peak torque, which is what it uses to accelerate the load. In a centrifugal pump, the load does not "couple" at a constant rate, it increases with speed. But the pump would still
try to run at the programmed speed, meaning the load (flow) will try to be at design values. But the motor would be incapable of supplying enough torque to keep it there. That, as you mentioned, would cause it to increase slip and thereby try to draw more current, to the point of overloading itself. Motors are "dumb animals".
Regardless, the drive was supposedly setup by a factory startup person. The motor winding connections should have been checked. The provider of the VFD (and the company that hired the startup person) is thinking they are going to invoice for 4hrs for supporting this since it wasn't a drive error. ....
I get your point, but having done countless VFD startups, I have rarely checked the motor connections (unless I made them myself) because if I were to crack open the motor peckerhead, I now own the motor; no think you. Most of the time the motor is already connected when I arrive, I will basically assume the installer was competent enough to know what they were doing.
On a few occasions I have NOTICED the lack of
performance and FOUND that the motor was incorrectly wired, so to that extent, I agree that if the system was able to operate under load, the VFD technician should have noticed. But that said, I have also been on MANY projects to start up the VFDs and the system is not ready to fully run, so I am provided with "simulated" loads, i.e. a fire hose supplying water to the pump. That can set up a tricky situation in that the dynamic head of the "test" is not the same as it will be in full operation, so you don't know what you don't know yet. In those cases I have learned to warn the users that this test setup may not be the final values, but contractors want to get paid, so they sign off on it. If I have to go back, it's at the expense of someone else.
