ABB RELION 670 Series Applications Manual page 268

Section 12
Control
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. Single-shot and multi-
shot are in use. The first shot can have a short delay, HSAR, or a longer delay, DAR. The second and
following reclosing shots have a rather long delay. When multiple shots are used the dead time
must harmonize with the breaker duty-cycle capacity.
Automatic-reclosing is usually started by the line protection and in particular by instantaneous
tripping of such protection. The auto-reclosing function can be inhibited (blocked) when certain
protection functions detecting permanent faults, such as shunt reactor, cable or busbar
protection are in operation. Back-up protection zones indicating faults outside the own line are
also connected to inhibit the Auto-Reclose.
Automatic-reclosing should not be attempted when closing a CB and energizing a line onto a fault
(SOTF), except when multiple-shots are used where shots 2 etc. will be started at SOTF. Likewise a
CB in a multi-breaker busbar arrangement which was not closed when a fault occurred should not
be closed by operation of the Auto-Reclosing function. Auto-Reclosing is often combined with a
release condition from synchronism check and dead line or dead busbar check. In order to limit the
stress on turbo-generator sets from Auto-Reclosing onto a permanent fault, one can arrange to
combine Auto-Reclosing with a synchronism check on line terminals close to such power stations
and attempt energizing from the side furthest away from the power station and perform the
synchronism check at the local end if the energizing was successful.
Transmission protection systems are usually sub-divided and provided with two redundant
protection IEDs. In such systems it is common to provide auto-reclosing in only one of the sub-
systems as the requirement is for fault clearance and a failure to reclose because of the auto-
recloser being out of service is not considered a major disturbance. If two auto-reclosers are
provided on the same breaker, the application must be carefully checked and normally one must
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1MRK 505 337-UUS A
Application manual