current flow in the sequential transfer mode is therefore longer in sequential
transfer mode than in simultaneous. Once open information from feeding circuit
breaker is received, transfer conditions are evaluated once more before close
command is given to the standby feeder. If conditions are not met, fast transfer
is canceled. Function will switch to next available transfer mode. Conditions to be
fulfilled before close command can be given are:
• READY (from Evaluation module) is TRUE
• Busbar voltage phase angle compared to standby feeder is still within angle
defined by
Max angle Diff FBBM
setting. Phase angle evaluation includes circuit
breaker closing time and frequency and frequency gradient of busbar voltage.
1
2
4
Window for FBBM
Window for fast transfer
3
5
Figure 942: Phase angle trajectory during fast sequential transfer (FBBM)
1
Synchronous conditions, transfer initiation
2 Circuit breaker opening
3 Circuit breaker opening detected, transfer conditions are evaluated before
close command is activated
4 Evaluated phase angle and amplitude of busbar voltage that would allow
close command
5 Evaluated phase angle and amplitude of busbar voltage that would not allow
close command, amplitude too low (Min busbar voltage) or phase angle
outside (Max angle Diff FBBM)
1MRS759142 F Control functions
REX640
Technical Manual
1775
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