ABB 615 Series ANSI, Техническое руководство

Страница: 508 / 713

1MAC050144-MB C
Section 7
Control functions
615 series ANSI 501
Technical Manual
7.2.5 Counters
The AR function contains six counters. Their values are stored in a semi-retain memory.
The counters are increased at the rising edge of the reclose command. The counters count
the following situations:
•
COUNTER
: counts every reclose command activation
•
CNT_SHOT1
: counts reclose commands that are executed from shot 1
•
CNT_SHOT2
: counts reclose commands that are executed from shot 2
•
CNT_SHOT3
: counts reclose commands that are executed from shot 3
•
CNT_SHOT4
: counts reclose commands that are executed from shot 4
•
CNT_SHOT5
: counts reclose commands that are executed from shot 5
The counters are disabled through communication with the DsaCnt parameter. When the
counters are disabled, the values are not updated.
The counters are reset through communication with the RsCnt parameter.
7.2.6 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.