The counters are reset through communication with the
CntRs parameter. The
same functionality can also be found in the clear menu (DARREC1 counters).
9.4.6
Application
Modern electric power systems can deliver energy to users very reliably. However,
different kind of faults can occur. Protection relays play an important role in
detecting failures or abnormalities in the system. They detect faults and give
commands for corresponding circuit breakers to isolate the defective element
before excessive damage or a possible power system collapse occurs. A fast
isolation also limits the disturbances caused for the healthy parts of the power
system.
The faults can be transient, semi-transient or permanent. For example, a permanent
fault in power cables means that there is a physical damage in the fault location
that must first be located and repaired before the network voltage can be restored.
In overhead lines, the insulating material between phase conductors is air. The
majority of the faults are flash-over arcing faults caused by lightning, for example.
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 autoreclose function minimizes interruptions in the power
system service and brings the power back on-line quickly and effortlessly.
The basic idea of the autoreclose function is simple. In overhead lines, where the
possibility of self-clearing faults is high, the autoreclose 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, autoreclose shots are allowed. If none of the trials is successful and
the fault persists, definite final tripping follows.
The autoreclose function can be used with every circuit breaker that has the ability
for a reclosing sequence. In DARREC autoreclose function the implementing method
of autoreclose sequences is patented by ABB.
Table 1002: Important definitions related to auto-reclosing
Autoreclose
shot
An operation where after a preset time the breaker is closed from the
breaker tripping caused by protection.
Autoreclose se-
quence
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 autoreclose operations. Since no
auto-reclosing follows, the circuit breaker remains open. This is called
final trip or definite trip.
Control functions
1MRS757644 H
1028
620 series
Technical Manual
