1-26 Functional Description
7000-TD002A-EN-P – September 2007
A T T E N T I O NA 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 TrqCmd0 Sensrlss and TrqCmd1 Sensrlss 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 FlxFbk VoltModel (342) and
StatFrqVoltModel (485) are used to ensure the reliability of the
analog feedback.
This feature is available in 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. Upon starting, if there is no detectable stator voltage, the
drive assumes that the motor is stationary. The output 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. If the drive reaches the maximum allowable speed
command without detecting any motor flux, then it will trip on a
motor stall fault. There are following possible causes of a motor stall
when starting:
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 TrqCmd0 Sensrlss, TrqCmd1
Sensrlss and Accel Time 1.
Test Modes (cont.)
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