FreqBandWidth
value)
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
). The following list gives some 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
12.1.7
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
Section 12
1MRK 511 365-UUS A
System protection and control
356
Phasor measurement unit RES670 2.1 ANSI
Technical manual
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