If the measured power drops under the drop-power1(2) value, the function will resetafter a set time DropDelay1(2). The reset means that the pickup signal will drop outand that the timer of the stage will reset.8.6.7.1 Low pass filtering SEMOD172136-39 v3In order to minimize the influence of the noise signal on the measurement it is possibleto introduce the recursive, low pass filtering of the measured values for S (P, Q). Thiswill 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 SOld Calculated= ⋅ + −( ) ⋅1EQUATION1959-ANSI V1 EN-US (Equation 37)WhereS is a new measured value to be used for the protection functionSold is the measured value given from the function in previous execution cycleSCalculated is the new calculated value in the present execution cycleTD is settable parameter by the end user which influence the filter propertiesDefault value for parameter TD is 0.00. With this value the new calculated value isimmediately 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 forTD=0.92 in case of slow operating functions.8.6.7.2 Calibration of analog inputs SEMOD172136-57 v3Measured currents and voltages used in the Power function can be calibrated to getclass 0.5 measuring accuracy. This is achieved by amplitude and angle compensation at5, 30 and 100% of rated current and voltage. The compensation below 5% and above100% is constant and linear in between, see example in figure 82.Section 8 1MRK 511 408-UUS ACurrent protection258 Phasor measurement unit RES670 2.2 ANSITechnical manual
