ABB Relion 670 Series Technical Reference Manual page 488

Section 7
Current protection
7.12.2.1
7.12.2.2
482
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:
( )
= × + - ×
S k S 1 k S
Old Calculated
EQUATION1959 V1 EN
Where
S is a new measured value to be used for the protection function
S is the measured value given from the function in previous execution cycle
old
S is the new calculated value in the present execution cycle
Calculated
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.
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 244.
1MRK505222-UUS C
(Equation 116)
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