ABB Relion REC670 Applications Manual page 246

Section 13
Control
To maximize the availability of the power system it is possible to choose single pole tripping
and automatic reclosing during single-phase faults and three pole tripping and automatic
reclosing during multi-phase faults. Three-phase automatic reclosing can be performed with
or without the use of a synchronicity 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 (earth fault protection) with the single pole tripping and the auto-reclosing
function. Attention shall also be paid to "pole discordance" that arises when circuit breakers
are provided with single pole operating devices. These breakers need pole discordance
protection. They must also be coordinated with the single pole auto-recloser and blocked
during the dead time when a normal discordance 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 1 1/2
breaker, 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 synchrocheck and dead line or dead busbar
240
1MRK 511 358-UEN A
Application manual