hysteresis should therefore be set to a smaller value. The drop-power value of stage1 can be
calculated with the
Power1(2)
,
Hysteresis1(2)
: drop-power1(2) =
Power1(2)
–
Hysteresis1(2)
For small power1 values the hysteresis1 may not be too big, because the drop-power1(2) would be
too small. In such cases, the hysteresis1 greater than (0.5 ·
Power1(2)
) is corrected to the minimal
value.
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 ant that the timer of the
stage will reset.
8.12.7.1 Low pass filtering
SEMOD172154-37 v4
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-US (Equation 161)
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.
8.12.7.2 Calibration of analog inputs
SEMOD172154-55 v2
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
295.
Section 8 1MRK 502 066-UUS B
Current protection
556
Technical manual
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