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Transfer control operation
Following is a description of the synchronous transfer
system operation. Figure 70 shows the elements that make
up an SC9000 EP Synchronous Transfer system.
Control elements colors and symbols
= de-energized
= energized
AFD bus
Figure 70. Synchronous transfer elements
Sequence of operation
1.
The AFD and feeder bus are energized (Figure 71).
Figure 71. AFD and feeder bus energized
2.
The PLC receives a Start Command from the
supervisory control system.
The PLC closes the appropriate motor select contactor
●
When the motor select contactor is closed, the PLC starts
●
the AFD. The AFD accelerates and operates the selected
motor at either a preset speed or a reference speed
(Figure 72)
= energized feeder bus
= contactor energized
and closed
SC9000 EP medium voltage drives IB020001EN—February 2016 www.eaton.com
Appendix D: Optional equipment
Figure 72. AFD runs selected motor at speed
3.
Sync UP
When the motor is required to transfer to the utility line,
●
the supervisory control instructs the PLC to send a
"Sync Up" command to the AFD
The AFD adjusts its output to match the utility line voltage,
●
frequency and phase angle
Once the AFD is synchronized with the utility line, the
●
selected motor's bypass contactor closes, connecting the
motor to the utility line, and the selected motor's select
contactor opens, disconnecting the motor from the AFD
bus (Figure 73)
Figure 73. Selected motor contactors switching
The AFD output reactor dampens any transient currents
●
that may occur during the transition
Once the transition is complete, the AFD shuts down and
●
waits for another Start command from the PLC
Now only the utility bus feeds the selected motor
●
(Figure 74)
73
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