Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 335)

Functional Description 5-27
7000 “C” Frame 7000L-UM300I-EN-P – June 2013
1. The motor has pulled out and stalled during starting due to
insufficient torque. The remedy for this is to increase the value
of some or all of the parameters Trq Command 0, Trq Command 1
and Accel Time 1.
2. The motor was already rotating but the flying start failed because
the drive passed through the low slip region too quickly to allow
the motor flux to build up. The solution to this problem is to
increase the value of parameter Accel Time 1. Most medium
voltage motors have a rotor time constant in the range of 1 to 5
seconds, and it can take a few seconds for the flux to rise to a
detectable level. Until flux is detected, the drive does not use the
normal speed ramp but continues to accelerate at the rate defined
by parameters Accel Time 1 and Ramp speed 1.
3. The motor is rotating in the direction opposite to the commanded
direction of rotation. The slip frequency will increase instead of
decreasing as the drive accelerates and no flux will be induced in
the motor.
4. The motor is rotating in the commanded direction but at a speed
higher than the commanded speed. The drive will reach the
commanded speed and trip before the slip frequency is low
enough to induce flux in the motor.
If the motor is coasting at a high enough speed (above about 40 Hz)
and the output contactor is closed, then the motor will self excite
with the drive motor filter capacitors and generate a high stator
voltage that the drive can detect. With software release 4.001, the
drive will re-synchronize to this voltage and drive will quickly
restart.
If the optional tachometer feedback is installed, then the drive knows
the speed of the motor at all times and can perform a flying start for
any speed or direction of rotation.