Residual voltage transfer
The residual voltage transfer is utilized when a connection in the 1
st
phase
coincidence is not possible. Following conditions must be met for residual voltage
transfer:
• transfer is running
• both breakers are open
• DISA_RES is FALSE
• setting
Ena Res V transfer allows transfer
• if transfer is initiated manually, then ENA_FASTONLY must be FALSE
The connection of the stand-by feeder takes place when the voltage of the busbar
has subsided to a preset, permissible value. The threshold value for the busbar
voltage for residual voltage transfer is set with setting
Residual voltage limit.
Residual voltage transfer is enabled with setting
Ena Res V transfer.
The connection takes place without assessment of the angle or of the difference
frequency, thus in unsynchronized fashion. Because the voltage of the busbars has
however reached a sufficiently low residual voltage value, the transient effects of
the connection are manageable (momentary jolt, current needed for users to run up
again, voltage reduction).
Main feeder
breaker
Stand-by
feeder breaker
Main feeder
breaker open
command
Stand-by
feeder close
command
1
2
3
4
Figure 946: Signal diagram of residual voltage transfer
1
Busbar voltage
2
Voltage difference between stand-by and busbar voltage
3
Main feeder current
4
Stand-by feeder current
If
DISA_RUN
input is active, transfer is not allowed to complete until input is
deactivated.
1MRS759142 F
Control functions
REX640
Technical Manual
1779