ABB Relion RES670, Technical Manual

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be used to extract low frequency signals. For example if 16,7 Hz signal shall be
extracted the minimum filter length in milliseconds shall be:
1000
3 180
16.7
ms
× =
EQUATION000028 V1 EN-US
(Equation 63)
Thus based on the data from Table 197 the minimum acceptable value for this
parameter would be “ FilterLength = 0.2 s” but more accurate results will be obtained
by using “ FilterLength = 0.5 s”
Second feature which is determined by the selected value for parameter FilterLength is
the capability of the filter to separate the desired signal from the other disturbing
signals which may have similar frequency value. Note that the filter output will be the
phasor with the highest magnitude within certain “pass frequency band” around the
SetFrequency . Table 198 defines the natural size of this pass frequency band for the
filter, depending on the selected value for parameter FilterLength .
Table 198: Pass frequency band due to FilterLength
Value for parameter FilterLength For 50Hz power system For 60Hz power system
0.1 s ±22.5 Hz ±27.0 Hz
0.2 s ±11.5 Hz ±14.0 Hz
0.5 s ±6.0 Hz ±7.2 Hz
1.0 s ±3.0 Hz ±3.6 Hz
2.0 s ±1.5 Hz ±1.8 Hz
4.0 s ±0.8 Hz ±1.0 Hz
Thus the longer length of the filter the better capability it has to reject the disturbing
signals close to the required frequency component and any other noise present in the
input signal waveform. For example if 46 Hz signal wants to be extracted in 50Hz
power system, then from
Table 198 it can be concluded that “ FilterLength =1,0 s” shall
be selected as a minimum value. However if frequency deviation of the fundamental
frequency signal in the power system are taken into account it may be advisable to
select “
FilterLength =2,0 s” for such application.
Note that in case when no clear magnitude peak exist in the set pass frequency band the
filter will return zero values for the phasor magnitude and angle while the signal
frequency will have value minus one. Finally the set value for parameter
FilterLength
also defines the response time of the filter after a step change of the measured signal.
The filter will correctly estimate the new signal magnitude once 75% of the filter
length has been filed with the new signal value (i.e. after the change).
1MRK 511 408-UUS A
Section 12
System protection and control
Phasor measurement unit RES670 2.2 ANSI 359
Technical manual