ABB REB670 Applications Manual page 309

1MRK 505 337-UUS -
Application manual
performed with or without the use of a synchronism check, and an energizing check, such
as dead line or dead busbar check.
During the single-pole open time there is an equivalent "series"-fault in the system
resulting in a flow of zero sequence current. It is therefore necessary to coordinate the
residual current protections (ground fault protection) with the single pole tripping and the
auto-reclosing function. Attention shall also be paid to "pole discrepancy" that arises
when circuit breakers are provided with single pole operating devices. These breakers
need pole discrepancy protection. They must also be coordinated with the single pole
auto-recloser and blocked during the dead time when a normal discrepancy occurs.
Alternatively, they should use a trip time longer than the set single phase dead time.
For the individual line breakers and auto-reclosing equipment, the "auto-reclosing open
time" expression is used. This is the dead time setting for the Auto-Recloser. During
simultaneous tripping and reclosing at the two line ends, auto-reclosing open time is
approximately equal to the line dead time. Otherwise these two times may differ as one
line end might have a slower trip than the other end which means that the line will not be
dead until both ends have opened.
If the fault is permanent, the line protection will trip again when reclosing is attempted in
order to clear the fault.
It is common to use one automatic reclosing function per line circuit-breaker (CB). When
one CB per line end is used, then there is one auto-reclosing function per line end. If auto-
reclosing functions are included in duplicated line protection, which means two auto-
reclosing functions per CB, one should take measures to avoid uncoordinated reclosing
commands. In breaker-and-a-half, double-breaker and ring bus arrangements, two CBs
per line end are operated. One auto-reclosing function per CB is recommended. Arranged
in such a way, sequential reclosing of the two CBs can be arranged with a priority circuit
available in the auto-reclose function. In case of a permanent fault and unsuccessful
reclosing of the first CB, reclosing of the second CB is cancelled and thus the stress on the
power system is limited. Another advantage with the breaker connected auto-recloser is
that checking that the breaker closed before the sequence, breaker prepared for an auto-
reclose sequence and so on. is much simpler.
The auto-reclosing function can be selected to perform single-phase and/or three-phase
automatic-reclosing from several single-shot to multiple-shot reclosing programs. The
three-phase auto-reclosing open time can be set to give either High-Speed Automatic
Reclosing (HSAR) or Delayed Automatic-Reclosing (DAR). These expressions, HSAR
and DAR, are mostly used for three-phase Reclosing as single phase is always high speed
to avoid maintaining the unsymmetrical condition. HSAR usually means a dead time of
less than 1 second.
In power transmission systems it is common practise to apply single and/or three phase,
single-shot Auto-Reclosing. In Sub-transmission and Distribution systems tripping and
auto-reclosing are usually three-phase. The mode of automatic-reclosing varies however.
Section 12
Control
303