I was a bit confused, because all of the information I could find on that drive at first stated that the maximum voltage is 460V. But I found a manual with reference to their having a 575V version for Canada, so that cleared things up from a logistic standpoint, but I still have my suspicions (see below). Something is amiss here and the evidence presented in this thread still points to the motor being under-fluxed. So I have to theorize based on what I can see in the available literature. Here are my working theories;
1) The drive is set for V/Hz mode of operation and someone turned on the "Variable Torque" mode. Most vector drives I have encountered will not allow you to put a drive in Auto-tune unless you have the control method set to Vector, but this drive doesn't seem to state any such restriction. That means you may THINK you are setting the motor tuning by doing an Auto-tune, but if someone left Fn 321 at setting 3, which is V/Hz mode (default) and 712 to a setting of 3 which is Variable Torque, the motor will still be providing less voltage at a given speed in an attempt to save energy. If the load needs constant torque then it will slow down, increase slip and draw more current.
2) Someone, at some point, got themselves messed up with programming of this drive and reset to the Factory Defaults. UNFORTUNATELY, the factory default values may in fact be for 460V motors, even on the 575V version of this drive! Here's my evidence, pasted from the 575V manual:
GE manual said:
5.3.2.2. Setting Motor Parameters
The AV-300i drive is factory set for use with 4-pole standard motors, either for 400V or 460V, to be operated up
to the nominal speed. Enter nameplate data recorded for the connected motor to ensure satisfactory performance.
Then later:
The BASIC MENU provides the parameters required for the initial commissioning of the drive. The data that is factory set for the default motor concerned refers to a four-pole machine for either 400V or 460V). The motor data in the DRIVE PARAMETER menu should be changed accordingly if different motors are used.
Now if I look at Fn `161, the Motor Voltage setting, it says in this manual that the default setting is in fact 575V. But being that the fact that the 575V version of this drive appears to be an afterthought in their product line (because there is no other literature saying it even exists), it's entirely possible that the mfr messed up and allows the Set to Factory Defaults function to reset the drive to 460V, the original design voltage. Just a hunch, but one based on my experience with other mfrs that attempted to sell 575V drives into Canada. Some of them just "tweak" a 480V design and call it good, and when you do that, nasty little details get missed.
If neither of those conditions exist, it also appears that this drive has something called a "dynamic regulation margin" (Fn 889) that artificially limits voltage above a certain speed. Here's how they describe it:
Example 2
Use of a standard motor 575 V / 60Hz
Application requiring total immunity from torque disturbances due to main voltage fluctuation.
Base voltage 575 V -15% = 490 V
Base frequency 60 Hz -15% = 51 Hz
The motor works at nominal flux until 51Hz (85% of the nominal speed), supplying full torque.
Over this frequency the voltage is regulated constant regulated, the flux is weakened and the motor supplies
constant power equal to 85% of the nominal (rated) power
If that is enabled, that would cause what you are describing if your load is demanding full torque at that speed.
God I love forensics, I shoulda been a detective... it's just not as satisfying when I'm not in front of the drive though.
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