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Functions
5.4
Busbar protection
5.4.1
Function description
5-16
The busbar protection function generates the TRIP command that is then multiplied
by means of peripheral modules to enable the output to all tripping circuit breakers. It
makes the r.m.s. values of the differential current I
available for display, stores events in the form of operational annunciations, fault
annunciations or spontaneous annunciations and outputs these via LED indicators or
signal relays. Measured values and annunciations are furthermore made available at
the RS485 interface for operation by PC using the DIGSI communication software.
The 7SS601 measuring system processes the externally formed sums of the
differential current I
and of the restraint current I
d
values, the protection function recognizes the presence of a fault in its associated
protection zone. Figure 5-17 shows the trip characteristic of the protection. The
characteristic is divided into a horizontal portion and a portion with a steadily rising
slope. Only value pairs of a differential and a restraint current that are both above the
characteristic constitute busbar faults that lead to a TRIP command. The level of the
horizontal portion of the characteristic is determined by the parameter ,G! ().
The slope of the rising portion can be varied by the setting of the parameter . IDF
(). The parameter ,' WKU () constitutes the selectable threshold for the
differential current supervision.
The algorithm of the 7SS601 measuring system is optimized for the fastest possible
tripping in case of a busbar short-circuit. The stability of the protection against external
faults is ensured if the transformer saturation occurs not before 3 ms.
ifferential current I
d
Id>
ID thr
0
Figure 5-17
Characteristic of the 7SS601 measuring system
d
. By means of these two measured
R
Tripping zone
Restraint
zone
and of the restraint current I
k = 0.80
.
.
.
.
.
.
.
.
k = 0,25
Normal load line
Restraint current I
7SS60 Manual
E50417-G1176-C132-A2
R
Pick-up
charact-
eristics
R
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Troubleshooting
