2 Functions
84
7ST6 Manual
E50417-G1176-C251-A3
2.4
High-Speed Overcurrent Protection
This function is optional, i.e. not included in all device variants.
In railway networks, close-in faults can lead to very high short-circuit currents. The
high-speed overcurrent protection issues in very short time the trip command to the
circuit breaker. This is advantageous especially with low power system frequencies
(long cycles) since it allows to quench the arc as quickly as possible.
2.4.1
Functional Description
General
The high-speed overcurrent protection works independently of other functions.
The high-speed overcurrent protection can be switched on or off by parameter set-
tings, or via binary inputs. The figure below shows the control logic:
Figure 2-16
Control logic of the instantaneous high-speed overcurrent protection function
The instantaneous value of the overhead contact line current, or the sum of the over-
head contact line current and the current of the negative feeder (2.1.3.1), is compared
with the setting
I HS O/C
(address
2404
).
When the settable delay time
T HS O/C
has expired, a trip command is issued.
The high-speed overcurrent protection has a fixed dropout delay which prevents that
the stage that has picked up drops out at the instant of the current zero crossing before
the set delay time has elapsed.
The figure below shows the pickup/trip logic of the high-speed overcurrent function.
Figure 2-17
Tripping logic of the high–speed overcurrent protection function
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