Low Pass Filtering - ABB RES670 Technical Manual

Section 8
Current protection
8.6.7.1
8.6.7.2
258
If the measured power drops under the drop-power1(2) value, the function will reset
after a set time DropDelay1(2). The reset means that the pickup signal will drop out
and that the timer of the stage will reset.

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 TD S TD S
1
Old
EQUATION1959-ANSI V1 EN-US
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
TD is settable parameter by the end user which influence the filter properties
Default value for parameter TD is 0.00. With this value the new calculated value is
immediately given out without any filtering (that is without any additional delay).
When TD is set to value bigger than 0, the filtering is enabled. A typical value for
TD=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 82.
)
⋅
Calculated
1MRK 511 408-UUS A
Phasor measurement unit RES670 2.2 ANSI
Technical manual
SEMOD172136-39 v3
(Equation 37)
SEMOD172136-57 v3