ABB RELION REX640 Technical Manual page 1527

1MRS759142 C
REX640
Technical Manual
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 1399: Important definitions related to autoreclosing
Autoreclose shot An operation where after a preset time the breaker is closed from the breaker
tripping caused by protection
Autoreclose A predefined method to do reclose attempts (shots) to restore the power system
sequence
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.
Section 9
Control functions
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