measured quantity. Filtering is performed in accordance with the following recursive
formula:
(1 )
Old Calculated
X k X k X= × + - ×
EQUATION1407 V1 EN (Equation 60)
where:
X is a new measured value (that is P, Q, S, V, I or PF) to be given out from the function
X
Old
is the measured value given from the measurement function in previous execution cycle
X
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. Appropriate value of k shall be
determined separately for every application. Some typical value for k =0.14.
Zero point clamping
In order to avoid erroneous measurements when either current or voltage signal is not
present, the magnitude level for current and voltage measurement is forced to zero. When
either current or voltage measurement is forced to zero automatically the measured values
for power (P, Q & S) and power factor are forced to zero as well. Since the measurement
supervision functionality, included in the CVMMXN function, is using these values the
zero clamping will influence the subsequent supervision (observe the possibility to do
zero point clamping within measurement supervision, see section
"Measurement
supervision").
Compensation facility
In order to compensate for small magnitude and angular errors in the complete
measurement chain (CT error, VT error, IED input transformer errors and so on.) it is
possible to perform on site calibration of the power measurement. This is achieved by
setting the complex constant which is then internally used within the function to multiply
the calculated complex apparent power S. This constant is set as magnitude (setting
parameter PowMagFact, default value 1.000) and angle (setting parameter
PowAngComp, default value 0.0 degrees). Default values for these two parameters are
done in such way that they do not influence internally calculated value (complex constant
has default value 1). In this way calibration, for specific operating range (for example,
around rated power) can be done at site. However, to perform this calibration it is
necessary to have an external power meter with high accuracy class available.
1MRK 511 287-UUS A Section 12
Monitoring
447
Technical manual
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