Directionality
If CT grounding parameter is set as described in section "Analog inputs", active and
reactive power will be measured always towards the protected object. This is shown in
the following figure 457.
Busbar
Protected
Object
P Q
ANSI05000373_2_en.vsd
52
IED
ANSI05000373 V2 EN
Figure 457: Internal IED directionality convention for P & Q measurements
Practically, it means that active and reactive power will have positive values when they
flow from the busbar towards the protected object and they will have negative values
when they flow from the protected object towards the busbar.
In some application, for example, when power is measured on the secondary side of the
power transformer it might be desirable, from the end client point of view, to have
actually opposite directional convention for active and reactive power measurements.
This can be easily achieved by setting parameter PowAngComp to value of 180.0
degrees. With such setting the active and reactive power will have positive values
when they flow from the protected object towards the busbar.
Frequency
Frequency is actually not calculated within measurement block. It is simply obtained
from the pre-processing block and then just given out from the measurement block as
an output.
15.1.2.3 Phase current measurement CMMXU
The Phase current measurement (CMMXU) function must be connected to three-phase
current input in the configuration tool to be operable. Currents handled in the function
can be calibrated to get better then class 0.5 measuring accuracy for internal use, on the
Section 15 1MRK505222-UUS C
Monitoring
906
Technical reference manual
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