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.
7.11.2.1 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:
S TD S TD S
Old Calculated
= ⋅ + −
( )
⋅1
EQUATION1959-ANSI V1 EN (Equation 106)
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
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.
7.11.2.2 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
240.
Section 7 1MRK505222-UUS C
Current protection
474
Technical reference manual
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