Differential Protection for Capacitor Banks
Overview of Functions
The function Differential protection for capacitor banks (ANSI 87C):
•
Detects ground faults and multiphase short circuits at capacitor banks
•
Detects ground faults during the operation of capacitors in systems with a grounded neutral point
•
Uses the necessary stabilization procedures during energizing operations
•
Trips safely and very fast in the case of internal high-current faults through an additional high-current
stage
Structure of the Function
The Differential capacitor bank protection function is used in the Capacitor bank diff protection function
group. The function depends upon application in the corresponding application template preconfigured by the
manufacturer and can be copied during the engineering into the corresponding function group.
The Capacitor bank diff function consists of the 2 tripping stages I-DIFF and I-DIFF fast. In addition, the trip-
ping stage I-DIFF unrestrained is available. You can select this tripping stage from the function catalog and
copy it into the Capacitor bank diff protection function group. The stages can be blocked, in addition you can
switch the stages on and off.
The Capacitor bank side function group has the following characteristics:
•
The side-related protection settings are performed
•
The side-related calculations are performed
•
All data (setting values, detected currents) are relayed to the Capacitor bank diff function group
The side-related protection functions can run in the Capacitor bank side function group, for example over-
load protection, overcurrent protection, etc.
[dweimcapbk-030314-01, 3, en_US]
Figure 7-44 Structure/Embedding of the Function
Function Description
Basic Principle of Differential Protection
Differential protection is based on a comparison of currents (Kirchhoff current law). When comparing the
current, use is made of the fact that a protected object uses the same current I in a non-faulty operating state
on both sides (dotted in Figure 7-45). This current flows into the range being observed on one side and leaves
it again on the other side. A current differential is a sure indication of a fault within the protected object. The
7.8
7.8.1
7.8.2
7.8.3
Capacitor Bank Protection
7.8 Differential Protection for Capacitor Banks
SIPROTEC 5, Overcurrent Protection, Manual 1043
C53000-G5040-C017-8, Edition 07.2017
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