ABB Relion 670 Series Applications Manual page 334

Section 15
Control
15.2.2 Application
Automatic reclosing is a well-established method for the restoration of service in a power
system after a transient line fault. The majority of line faults are flashovers, which are transient
by nature. When the power line is switched off by the operation of line protection and line
breakers, the arc de-ionizes and recovers its ability to withstand voltage at a somewhat
variable rate. Thus, a certain dead time with a de-energized line is necessary. Line service can
then be resumed by automatic reclosing of the line breakers. The dead time selected should be
long enough to ensure a high probability of arc de-ionization and successful reclosing.
For individual line breakers, auto reclosing equipment, the required circuit breaker dead time
is used to determine the "dead time" setting value. When simultaneous tripping and reclosing
at the two line ends occurs, line dead time is approximately equal to the auto recloser "dead
time". If the auto reclosing dead time and line "dead time" differ then, the line will be energized
until the breakers at both ends have opened.
Line
protection
Operate time
Circuit
breaker
Auto-reclosing
function
IEC04000146 V3 EN-US
Figure 147: 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
328
Closed
Open
Break time
Fault duration
Set AR dead time
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Operate time
Closing time
Circuit breaker open time Fault duration
Reclaim time
1MRK 511 401-UEN Rev. K
Break time
IEC04000146-3-en.vsd
Bay control REC670
Application manual
M12391-3 v8