1000
3
180
16.7
ms
×
=
EQUATION000028 V1 EN
(Equation 62)
Thus based on the data from
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
.
defines the natural size of this pass frequency band for the filter, depending on
the selected value for parameter
FilterLength
.
Table 200:
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
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).
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:
1MRK 511 365-UUS A
Section 12
System protection and control
Phasor measurement unit RES670 2.1 ANSI
355
Technical manual
Содержание Relion 670 Series RES670
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