Table of Contents
Advertisement
Section 12
Control
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.
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 be the master and be connected to inhibit the other auto recloser if it has started. This
inhibit can, for example, be done from an auto recloser for 3-phase operation in progress
signal.
When Single and/or three phase auto reclosing is considered, there are a number of cases
where the tripping shall be three phase anyway. For example:
•
Evolving fault where the fault during the dead-time spreads to another phase. The other
two phases must then be tripped and a three phase dead-time and auto reclose initiated
•
Permanent fault
•
Fault during three-phase dead time
•
Auto recloser out of service or circuit breaker not ready for an auto reclosing cycle
266
1MRK 505 370-UEN D
Busbar protection REB670
Application manual
Advertisement
Table of Contents
