Filter Calculation Example - ABB RES670 Technical Manual

Section 12
System protection and control
12.1.7
360
If for any reason this natural frequency band shall be extended (e.g. to get accurate but
wider filter) it is possible to increase the pass band by entering the value different from
zero for parameter FreqBandWidth. In such case the total filter pass band can be
defined as:
± (value given in Table 198
Example if in 60Hz system the selected values are "FilterLength =1.0 s" and
"FreqBandWidth = 5.0" the total filter pass band will be ±(3.6+5.0/2)= ± 6.1 Hz.
It shall be noted that the phasor calculation is relatively computation demanding
(required certain amount of the CPU processing time). In order to control the CPU
usage for this filter, the setting parameter OverLap is used. This setting parameter
defines how often the new phasor value is calculated during time period defined by the
set value for the parameter FilterLength (see
examples how this parameter influence the calculation rate for the extracted phasor:
• when OverLap=0% the new phasor value is calculated only once per FilterLength
• when OverLap=50% the new phasor value is calculated two times per
FilterLength
• when OverLap=75% the new phasor value is calculated four times per
FilterLength
• when OverLap=90% the new phasor value is calculated ten times per FilterLength

Filter calculation example

In the following Figure an example from an installation of this filter on a large, 50 Hz
turbo generator with a rating in excess of 1000 MVA is presented. In this installation
filter is used to measure the stator sub-synchronous resonance currents. For this
particular installation the following settings were used for the filter:
• SetFrequency= 31.0 Hz
• FilterLength= 1.0 s
• OverLap = 75%
• FreqBandWidth= 0.0 Hz
+ one-half of the set FreqBandWidth value)
Table 197). The following list gives some
Phasor measurement unit RES670 2.2 ANSI
1MRK 511 408-UUS A
GUID-F5828B0A-CED3-483E-B5B1-F389C3C2AEFB v3
Technical manual