Application Specific Features
7.7 Synchronous Transfer
Product User Manual
164 Operating Instructions, Version AE 12/2009, A5E01454341C
VFD Transfer Permissive
WARNING
The VFD output contactor and motor line contactors should never be simultaneously closed
if the digital output signal "VFD Transfer Permissive" is low, or when the VFD input is not
energized. Failure to ensure that this condition does not occur could result in severe
damage to the VFD power cells.
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Figure 7-1 Multi-Motor, Synchronous Transfer
Figure "Multi-Motor, Synchronous Transfer" provides a block diagram showing the VFD
configuration for synchronous transfer for a two motor implementation.
Note
A PLC is recommended for multi-motor synchronous transfer applications. This PLC and its
logic can be supplied by Siemens engineering to coordinate the transfer sequence and also
control the switchgear. In addition, motor protection relays are recommended since the VFD
cannot protect a motor operating from the line.
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