Only a short interruption is needed for extinguishing the arc. These faults are transient
by nature.
A semi-transient fault can be caused for example by a bird or a tree branch falling on
the overhead line. The fault disappears on its own if the fault current burns the branch
or the wind blows it away.
Transient and semi-transient faults can be cleared by momentarily de-energizing the
power line. Using the auto-reclose function minimizes interruptions in the power
system service and brings the power back on-line quickly and effortlessly.
The basic idea of the auto-reclose function is simple. In overhead lines, where the
possibility of self-clearing faults is high, the auto-reclose function tries to restore the
power by reclosing the breaker. This is a method to get the power system back into
normal operation by removing the transient or semi-transient faults. Several trials,
that is, auto-reclose shots are allowed. If none of the trials is successful and the fault
persists, definite final tripping follows.
The auto-reclose function can be used with every circuit breaker that has the ability
for a reclosing sequence. In DARREC auto-reclose function the implementing
method of auto-reclose sequences is patented by ABB
Table 92: Important definitions related to auto-reclosing
auto-reclose shot
an operation where after a preset time the breaker is closed from the breaker
tripping caused by protection
auto-reclose
sequence
a predefined method to do reclose attempts (shots) to restore the power system
SOTF If the protection detects a fault immediately after an open circuit breaker has been
closed, it indicates that the fault was already there. It can be, for example, a
forgotten earthing after maintenance work. Such closing of the circuit breaker is
known as switch on to fault. Autoreclosing in such conditions is prohibited.
final trip Occurs in case of a permanent fault, when the circuit breaker is opened for the last
time after all programmed auto-reclose operations. Since no auto-reclosing
follows, the circuit breaker remains open. This is called final trip or definite trip.
10.4.3.1 Shot initiation
In some applications, the START signal is used for initiating or blocking autoreclose
shots, in other applications the OPERATE command is needed. In its simplest, the
auto-reclose function is initiated after the protection has detected a fault, issued a trip
and opened the breaker. One input is enough for initiating the function.
The function consists of six individual initiation lines INIT_1, INIT_2 ..
INIT 6 and delayed initiation lines DEL_INIT_x. The user can use as many of the
initiation lines as required. Using only one line makes setting easier, whereas by using
multiple lines, higher functionality can be achieved. Basically, there are no
differences between the initiation lines, except that the lines 2, 3 and 4 have the
delayed initiation DEL_INIT inputs, and lines 1, 5 and 6 do not.
1MRS756378 D Section 10
Control functions
REF615 215
Application Manual
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