ABB REB670 Applications Manual page 307

1MRK 505 337-UUS -
Application manual
closed, all other feeder which have been connected to the same bus, are automatically put
back into service.
Sensitive differential protection level available in REB670 can be used during such
operation, if increased sensitivity from busbar protection is required. Such busbar
restoration logic can be implemented by using optionally available autoreclosing
functions and built-in logical gates. Two autoreclosing functions are available, one for
each zone.
Automatic reclosing is a well-established method for the restoration of service in a power
system after a transient line fault. The majority of line faults are flashover arcs, which are
transient by nature. When the power line is switched off by the operation of line protection
and line breakers, the arc de-ionizes and recovers its ability to withstand voltage at a
somewhat variable rate. Thus, a certain dead time with a de-energized line is necessary.
Line service can then be resumed by automatic reclosing of the line breakers. The dead
time selected should be long enough to ensure a high probability of arc de-ionization and
successful reclosing.
For individual line breakers, auto-reclosing equipment, the auto-reclosing open time is
used to determine line "dead time". When simultaneous tripping and reclosing at the two
line ends occurs, auto-reclosing open time is approximately equal to the line "dead time".
If the open time and dead time differ then, the line will be energized until the breakers at
both ends have opened.
Section 12
Control
301