[dw_charac_function_trans-dif, 1, en_US]
Figure 7-50 Operate Curve of the Differential Protection Function
Measurand Processing
Amount Correction
Since the current transformers cannot be adapted exactly to the rated currents of the protected object with
regard to their primary rated data, a standardization to the nominal sizes of the protected object takes place.
The conversion occurs every sampling time (thus, for instantaneous values). The differential protection func-
tion processes 20 sampled values per period. In addition, the sampled values tracked are used. A high degree
of accuracy can be attained over the entire tracking range (from 10 Hz to 80 Hz).
The Idiff-fast tripping stage works on non-frequency tracked values and thus, implements fast operate times
with low frequencies.
The amount is adapted via the following formula:
[fobetr07-170712-01.tif, 1, en_US]
i
phsx
* Adapted instantaneous value per phase (x = A, B, C)
i
phsx
Instantaneous value per phase (x = A, B, C)
k Correction value per measuring point
I
rated prim,Sx
Primary transformer rated current per measuring point
I
rated obj,Sx
Primary rated current of the protected object
S
rated,ref
Reference power (maximum rated apparent power of the protected object)
V
rated,Sx
Rated voltage of the respective side (measuring point) of the protected object
NOTE
For more than 2 capacitor bank sides (teed feeder), , the winding with the highest power is used as the
reference winding. If several sides have the same highest amount of power, then the highest current side is
selected as reference side. The amount of the neutral-point transformer is also adapted according to the
previous formula. In this case, the amount should be adapted to the side with the greatest power.
Vector-Group Correction
The vector groups of the capacitor bank sides occur due to couplings that are different on each side. There-
fore, the measured currents cannot be used directly for summation. The vector-group correction replicates the
coupling of the capacitors and makes the measured currents comparable. The correction occurs such that each
Capacitor Bank Protection
7.8 Differential Protection for Capacitor Banks
1048 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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