Filter for RMS Value Gain
Description
The function block Filter can be used to adapt the RMS value for 2 means:
•
To gain harmonics in a defined way. Higher harmonics can stress the protected object thermally more
than lower harmonics. This is the case for reactors applied in AC filters. In addition, the amplitude attenu-
ation of higher frequencies due to the anti-aliasing filter of the device is automatically compensated by
the filter
•
To only compensate the amplitude attenuation of higher frequencies due to the anti-aliasing filter
The filter gain (amplitude response) is realized by a 9-order FIR filter.
Logic
[lo_TOLP_FilterStage, 1, en_US]
Figure 6-7 Logic Diagram of the Function Block Filter
The FIR filter gains the 8-kHz sampled values according to the set filter coefficients. Afterwards, the RMS value
is calculated. The symmetrical 9-order filter coefficients are set via the values of the respective parameters
h(0), h(1), h(2), h(3), and h(4).
NOTE
A FIR-filter configuration tool is provided as an auxiliary PC tool. With this PC tool, the coefficients h(0),
h(1), h(2), h(3), h(4) of the FIR filter are generated according to the required gain factors (amplitude
response). The tool can be obtained from the SIPROTEC download area. For more information about the
tool, refer to the tool help function.
The gained RMS value is delivered to the protection stages only when the function block Filter is instantiated
and the parameter Enable filter is set as yes. Otherwise, the normal RMS value is used.
Functional Measured Values
Values
Description Primary Secondary % Referenced to
Iph:A Gained RMS measured
value of current A
kA A Parameter Rated current
Iph:B Gained RMS measured
value of current B
kA A Parameter Rated current
6.3.3
6.3.3.1
Protection and Automation Functions
6.3 Overcurrent Protection, Phases
SIPROTEC 5, Overcurrent Protection, Manual 325
C53000-G5040-C017-8, Edition 07.2017
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