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
“Prepare three-phase tripping” is then used to switch the tripping to three-phase.
This signal is generated by the auto recloser and connected to the trip function
block and also connected outside the IED through IO when a common auto
recloser is provided for two sub-systems. An alternative signal “Prepare 1-phase
tripping” is also provided and can be used as an alternative when the autorecloser is
shared with another subsystem. This provides a fail safe connection so that even a
failure in the IED with the auto recloser will mean that the other sub-system will
start a three-phase trip.
Section 12 1MRK 505 393-UEN B
Control
232 Line differential protection RED650 2.2 IEC
Application manual
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