Open
Closed
Operate time
Line
protection
Circuit
breaker
Break time
Trip command
Contacts separated
Arc extinguishers
Fault duration Circuit breaker open time
Fault duration
Resets
Instant of fault
Operates
Break timeClosing time
Operate time
Fault
Operates
Resets
Close command
Contact closed
Set AR dead time Reclaim time
Auto-reclosing
function
Start AR
Reclosing
command
AR reset
IEC04000146-3-en.vsd
IEC04000146 V3 EN-US
Figure 130: Single-shot automatic reclosing at a permanent fault
Single-phase tripping and single-phase automatic reclosing is a way of limiting the effect of a
single-phase line fault on power system operation. Especially at higher voltage levels, the
majority of faults are of single-phase type (around 90%). To maintain system stability in power
systems with limited meshing or parallel routing single-phase auto reclosing is of particular
value. During the single-phase dead time the system is still capable of transmitting load on the
two healthy phases and the system is still synchronized. It requires that each circuit breaker
pole can be operated individually, which is usually the case for higher transmission voltages.
A somewhat longer dead time may be required for single-phase reclosing compared to high-
speed three-phase reclosing. This is due to the influence on the fault arc from the voltage and
the current in the non-faulted phases.
To maximize the availability of the power system it is possible to choose single-phase tripping
and automatic reclosing during single-phase faults and three-phase tripping and automatic
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.
1MRK 505 370-UEN D Section 12
Control
Busbar protection REB670 265
Application manual
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