ABB Relion 670 Series RES670, Technical Manual

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8.7.7.1 Low pass filtering
In order to minimize the influence of the noise signal on the measurement it is possible to
introduce the recursive, low pass filtering of the measured values for S (P, Q). This will
make slower measurement response to the step changes in the measured quantity.
Filtering is performed in accordance with the following recursive formula:
( )
Old Calculated
S k S 1 k S
= × + - ×
EQUATION1959 V1 EN
(Equation 47)
Where
S is a new measured value to be used for the protection function
S
old
is the measured value given from the function in previous execution cycle
S
Calculated
is the new calculated value in the present execution cycle
k is settable parameter by the end user which influence the filter properties
Default value for parameter k is 0.00 . With this value the new calculated value is
immediately given out without any filtering (that is, without any additional delay). When k
is set to value bigger than 0, the filtering is enabled. A typical value for k = 0.92 in case
of slow operating functions.
8.7.7.2 Calibration of analog inputs
Measured currents and voltages used in the Power function can be calibrated to get class
0.5 measuring accuracy. This is achieved by amplitude and angle compensation at 5, 30
and 100% of rated current and voltage. The compensation below 5% and above 100% is
constant and linear in between, see example in figure
83 .
1MRK 511 365-UUS A
Section 8
Current protection
Phasor measurement unit RES670 2.1 ANSI 265
Technical manual