Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C Frame) - Classic Control - Manual (Page 334)

5-26 Functional Description
7000L-UM300I-EN-P – June 2013 7000 “C” Frame
A T T E N T I O N A T T E N T I O N Open circuit test mode should not be used
when the drive is connected to a load unless
an output contactor is provided.
Setting Operating Mode to Open Loop

selects a diagnostic mode
in which the drive is run in an open loop manner without closing any
of the feedback loops on the motor side (Speed and Flux regulators).
Parameters Trq Command 0 and Trq Command 1 are used to inject
motor current at a small stator frequency (typically 10% of Rated
Line Frequency). Motor will be turning in this mode and drive
analog flux feedback variables Flux from Voltage (342) and Stator
Freq V (485) are used to ensure the reliability of the analog
feedback.
 This feature is available in firmware release 4.001 and higher for drives running induction
motors only.
Flying Start (Induction Motor)
Using this feature, the PowerFlex 7000 AC drive is capable of
restarting a motor that is not stationary but is already rotating. In
normal operation, the output of the drive is synchronized with the
motor flux, which is derived from the stator voltage and current
feedback. If there is no motor current, then whether the motor is
rotating or stationary, it does not generate any significant voltage and
it is not possible to determine the stator frequency. If there is no
detectable stator voltage, the drive assumes that the motor is
stationary, because this is the most likely case. Therefore, when the
drive is started, the frequency starts from an initial value of zero and
ramps up until motor flux is detected. Significant flux is created in
the motor only when the slip frequency (i.e. the difference between
the applied stator frequency and rotor frequency) is small. When the
drive is started with the motor stationary, the initial slip frequency is
small and the motor flux builds up fairly quickly. But, if the motor is
already spinning, then very little flux will be induced until the stator
frequency is quite close to the rotor frequency, at which time the
motor flux will suddenly rise to a level sufficient for the drive to
detect and synchronize to. If the drive reaches the commanded speed
without detecting any motor flux, then it will trip on a motor stall
fault. There are four possible causes of a motor stall when starting: