ABB Relion 670 Series Applications Manual page 335

1MRK 511 401-UEN Rev. K
reclosing during multi-phase faults. Three-phase automatic reclosing can be performed with
or without the use of synchrocheck.
During the single-phase dead 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-phase tripping and the auto reclosing
function. Attention shall also be paid to "pole discordance" that arises when circuit breakers
are provided with single-phase operating devices. These breakers need pole discordance
protection. They must also be coordinated with the single-phase 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 dead 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 dead 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- recloser per line end. If auto reclosers are
included in duplicated line protection, which means two auto reclosers 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 recloser per CB is
recommended. Arranged in such a way, that sequential reclosing of the two CBs can be
arranged with a priority circuit available in the auto recloser. 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.
The auto recloser 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 dead 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 auto reclosing as single-phase auto reclosing 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 practice 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 recloser 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 typically connected to inhibit the auto recloser.
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 recloser. Auto reclosing is often
combined with a release condition from synchrocheck 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 synchrocheck on line terminals close to such
power stations and attempt energizing from the side furthest away from the power station
and perform the synchrocheck at the local end if the energizing was successful.
Bay control REC670
Application manual
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Section 15
Control
329