These DFT reference block settings decide DFT reference for DFT calculations. The
settings InternalDFTRef will use fixed DFT reference based on set system frequency. The
setting DFTRefGrpn (where n is a number from 1 to 12) will use the SMAI block
numbered n, within its task, as reference for the adaptive frequency tracking. The setting
ExternalDFTRef will use reference based on what is connected to input DFTSPFC.
The setting ConnectionType: Connection type for that specific instance (n) of the SMAI
(if it is Ph-N or Ph-Ph). Depending on connection type setting the not connected Ph-N or
Ph-Ph outputs will be calculated.
Negation: Negation means rotation with 180
0
of the vectors. If the user wants to negate the
3ph signal, it is possible to choose to negate only the phase signals Negate3Ph, only the
neutral signal NegateN or both Negate3Ph+N.
MinValFreqMeas: The minimum value of the voltage for which the frequency is
calculated, expressed as percent of the voltage in the selected Global Base voltage group
(n) (for each instance 1<n<6).
Settings DFTRefExtOut and DFTReference shall be set to default value
InternalDFTRef if no VT inputs are available.
Even if the user sets the AnalogInputType of a SMAI block to “Current”,
the MinValFreqMeas is still visible. However, using the current channel
values as base for frequency measurement is not recommendable for a
number of reasons, not last among them being the low level of currents
that one can have in normal operating conditions.
Example of adaptive frequency tracking
Section 15 1MRK 511 286-UUS A
Basic IED functions
336
Application manual
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