what would you do in this situation:
We wrote a pump motor purchase spec which had a requirement for the motor to be able to start and come to full speed with an available voltage of 80% at the terminals.
Motor Vendor agreed and build the motor to this spec.
After testing, vendor finds motor cannot actually start the load with 80% voltage at terminals. They are requesting our system voltage to be stiffer (closer to 90%).
would appreciate your input, thanks
I assume we are looking at a cage induction motor?
As Skeshesh has pointed out, if the vendor has agreed to comply with the specification then they have not met their side of the contract and, all other things being equal, it ought to be incumbent on them to remedy that and meet the costs of doing so. Often things are not so tidy as rcwilson has noted.
But I think that there are no easy, cheap, or quick fixes if the 80% is cast in tablets of stone. So maybe that is a starting point for technical solutions.
If the 80% requirement is because the starting current of this particular motor would cause such a drop in voltage then a bigger motor won't help.
At 80% voltage the motor will generate about 64% of the torque it would at full voltage. For a centrifugal pump, the load torque varies as the square of the speed so, if the motor is rated to deliver
just the pump absorbed power at rated speed, it would get to 80% of full speed or a slip of 0.2. At that point the current would have dropped off some and the voltage drop would be less than that at initial starting. In my experience on pump sets, the motor is usually sized to have some margin over pump absorbed power so the speed might get a bit higher, the current a bit lower and the voltage regulation a bit less. As the others have pointed out, maybe some more work needs to be done that would allow some flexibility with the 80% voltage. Getting up to rated speed and load with 80% voltage would be outside the parameters of most motors.