Application Specific Features
7.7 Synchronous Transfer
Product User Manual
168 Operating Instructions, Version AE 12/2009, A5E01454341C
5. Once the output current from the VFD reaches a predetermined level, the VFD signals
that the line contactor can be opened. The output current will be limited to the maximum
torque limit set in the NXG control.
Note
The VFD will remain in the Down Transfer state as long as the "Down Transfer Request"
signal is set or until a VFD stop command is issued. If a VFD fault occurs at any time prio
to opening the Line Contactor, the motor should remain connected to the line and all input
flags to the VFD should be cleared.
As a rule of thumb, a Down Transfer typically will be complete within 30-60 seconds.
There is no defined maximum or minimum time period required for opening the line
contactor after the VFD issues the status flag to allow the Line Contactor to be opened.
6. Once the line contactor is opened, the Down Transfer Request must be removed and the
VFD will control the motor as commanded. The run request must be maintained, and
desired speed reference should be present to ensure a bumpless transition.
Note
For induction machines: to maintain bumpless down transfer, the speed reference source
to be used upon completion of down transfer should preset the speed reference to the
mechanical shaft speed of the motor at rated line frequency (i.e., externally compensate
for slip, where the speed reference should be set to 100% - RatedSlip).
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