Siemens 7SJ85 - Page 1024

The rated current I
C-rated
is determined from the rated capacity and the rated voltage across the bank. Both
values are listed in the Technical Data for the capacitor. Take note of the following:
•
The rated voltage for the capacitor also takes harmonics into account. This is not the rated voltage of the
system.
•
The rated voltage to be used is the voltage applied across the capacitor; depending on the application,
this can be a phase-to-phase or phase-to-ground voltage.
Example: Determining the Capacitor Rated Current for a Capacitor in a Star Connection
[dw_UC-Y-Schalt-110813, 1, en_US]
Figure 7-33 Capacitor in Star Connection
Rated voltage of the system 220 kV
Rated capacity per phase 5.233 µF
Capacitor rated voltage V
C-rated
192.30 kVrms
Rated frequency f 50 Hz
I
C-rated
= ωC × U
C-rated
= 2πf × C × U
C-rated
= 2 π 50 × 5.233 10
-6
× 192.3 10
3
[Hz × F × U] = 316.1 [A]
Parameter: Threshold
•
Default setting (_:13861:3) Threshold = 1.10
The peak voltage determined is then set with reference to the rated voltage of the capacitor. The threshold
value is thus set as a referenced quantity.
The points on the characteristic curve defined in the Standards IEC 60871-1:2005 and IEEE Std 1036-2010
result from a threshold setting of 1.10 (see Figure 7-32). Threshold values differing from this shift the charac-
teristic as shown in Figure 7-32.
Siemens recommends using the default setting.
Parameter: Dropout principle
•
Default setting (_:13861:103) Dropout principle = with down integration
Use the parameter Dropout principle to select the method for the dropout of the stage:
Parameter Value
Description
with down integra-
tion
If the measurand for the dropout threshold falls below the limit, the pickup
drops out immediately.
If the value drops below the pickup threshold, the internal integral value that
depends on the selected down integration time is reduced from 100 % to 0 %
with dropout delay
If the measurand falls below the dropout threshold, the measurand remains
active for the duration of the preset dropout delay. The integral value remains
frozen during this time.
Capacitor Bank Protection
7.6 Peak Overvoltage Protection for Capacitors
1024 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017