Trip Logic of the Differential Protection Function I-DIFF
Figure 7-56 shows the trip logic. If the characteristic curve is exceeded (see Figure 7-51) a pickup occurs. Redi-
rection of the information for tripping can be blocked by the additional functions.
Blocking is possible through use of the following influencing variables:
•
Recognition of external faults that can simulate an internal fault through transformer saturation
•
Recognition of the connection process (2nd harmonic)
In addition, in case of blocking due to an
external error
, a Crossblock mechanism comes into effect.
[loauscod-290414-01, 1, en_US]
Figure 7-56
Trip Logic of I-DIFF
I-DIFF Fast Differential Protection Function
As a supplement to the I-DIFF differential protection function, the function I-DIFF fast is available. The main
task consists in switching off high-current internal faults in the shortest amount of time. The method controls
current-transformer saturation and is stable in the event of external transverse faults (integration in breaker-
and-a-half arrangements).
Metrologically, 2 methods are combined:
•
Instantaneous-value method
•
Filter-based method
Instantaneous-Value Method
Through the instantaneous-values method, an immediate evaluation of the sampled values of the differential
i
Diff
(t) and restraint current i
rest
(t) occurs. The absolute-value and vector-group adapted currents (i*) are also
Capacitor Bank Protection
7.8 Differential Protection for Capacitor Banks
1054 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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