To avoid an overfunction when connecting the capacitor banks, you can set the parameter Starting
detection = Yes. Siemens recommends using the setting Starting detection = Yes.
Parameter: Thresh. startup detection
•
Default setting (_:11041:107) Thresh. startup detection = 0.1 I/Irated,obj
If the restraint current falls below this threshold value, the subsequently set characteristic-curve increase
becomes effective with activated function. The default setting value of 0.1 I/Irated,obj is recommended
for the application.
Parameter: Factor increasing char.
•
Default setting (_:11041:108) Factor increasing char. = 2.0
An increase to the value 2.0 has proven itself to be sufficient for many applications.
Parameter: Max. perm. Start. time
•
Default setting (_:11041:109) Max. perm. Start. time = 5.0 s
The setting value must lie above the maximum permissible starting time of the connected capacitor bank. To
ensure tripping by the capacitor-bank protection (make time/starting time supervision) and avoid overfunc-
tions, select a somewhat longer time (factor of 1.2 or higher).
Parameter: Factor increasing char. DC (DC-Component Detection)
•
Default setting (_:11041:110) Factor increasing char. DC = 2.3
DC-component detection is always active. As a result of the DC components, transmission problems can arise
(for example, phase-angle rotations) in current transformers with small currents flowing. For this reason, the
Threshold and the Slope 1 are raised by the set factor. The default setting of 2.3 has proven itself with
numerous applications.
Parameter: Blocking with 2. harmonic (Inrush-Current Detection)
•
Default setting (_:11041:115) Blocking with 2. harmonic = No
The inrush-current detection is not necessary for the capacitor-bank applications.
Parameter: 2nd harmonic content
•
Default setting (_:11041:116) 2nd harmonic content = 15 %
For many practical applications, the default setting value of 15 % has proven useful. In exceptional cases, the
setting value can be decreased with a small proportion of 2nd harmonic. Avoid a setting under 10 %, however.
With an internal fault and current-transformer saturation, some proportion of 2nd harmonic also arises. Too
sensitive of a setting leads to a blocking of the protection function.
Parameter: Crossblock. time 2nd har.
•
Default setting (_:11041:117) Crossblock. time 2nd har. = 0.00 s
Since the inrush currents develop differently in the 3 phases, the pickup value, for example, is not attained in
a phase, but the differential current exceeds the characteristic curve. Corrective action creates a mutual
blocking. If a time unequal to 0 s is set, the crossblock function works. If an overfunction arises, the setting
cannot be made until commissioning takes place. Do not set the duration for an excessive amount of time.
Practical values showed a setting between 3 and 5 periods.
Detection of External Faults
In Figure 7-66, the range Add-on stabilization of external faults is represented. The range is described by
the parameters Threshold add-on stabiliz. and Slope 1. With an external short circuit, the differen-
tial currents can increase beyond this range and reach into the tripping area. With the following parameters,
time-limited blocking can be performed.
Capacitor Bank Protection
7.8 Differential Protection for Capacitor Banks
SIPROTEC 5, Overcurrent Protection, Manual 1065
C53000-G5040-C017-8, Edition 07.2017
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