ABB Relion 670 Series RES670, Technical Manual

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• Sensitive reverse power protection
• Stator or rotor ground fault protection for special injection frequencies (e.g. 25Hz)
• etc.
The filter output can also be connected to the measurement function blocks such as
CVMMXN (Measurements), CMMXU (Phase current measurement), VMMXU (Phase-
phase voltage measurement), etc.
The filter has as well additional capability to report the exact frequency of the extracted
signal. Thus the user can check the actual frequency of some phenomenon in the power
system (e.g. frequency of the sub-synchronous currents) and compare it with expected
value obtained previously by either calculation or simulation. For the whole three-phase
filter group the frequency of the signal connected to the first input (i.e. phase A) is
reported. This value can be then used either by over-/under-frequency protections or
reported to the built-in HMI or any other external client via the measurement blocks such
is the CVMMXN.
How many samples in the memory are used for the phasor calculation depends on the
setting parameter
FilterLength . Table 199 gives overview of the used number of samples
for phasor calculation by the filter. Note that the used number of samples is always a power
of number two.
Table 199: Length of the filtering window
Value for parameter
FilterLength
Used No of samples for
calculation (fixed,
independent from rated
frequency)
Corresponding length of
the input waveform in
miliseconds for 50Hz
power system
Corresponding length of
the input waveform in
miliseconds for 60Hz
power system
0.1 s
128 = 2 7
128 ms 107 ms
0.2 s
256 = 2
8
256 ms 213 ms
0.5 s
512 = 2
9
512 ms 427 ms
1.0 s
1024 = 2
10
1024 ms 853 ms
2.0 s
2048 = 2
11
2048 ms 1707 ms
4.0 s
4096 = 2
12 4096 ms 3413 ms
Note that the selected value for the parameter FilterLength automatically defines certain
filter properties as described below:
First in order to secure proper filter operation the selected length of the filter shall always
be longer than three complete periods of the signal which shall be extracted. Actually the
best results are obtained if at least five complete periods are available within the filtering
window. Thus, this filter feature will limit which filter lengths can 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:
Section 12
1MRK 511 365-UUS A
System protection and control
354 Phasor measurement unit RES670 2.1 ANSI
Technical manual