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Section 15
Basic IED functions
484
•
All three inputs GRPxLx should be connected to SMAI for calculating sequence
components for ConnectionType set to Ph-N.
•
At least two inputs GRPxLx should be connected to SMAI for calculating the
positive and negative sequence component for ConnectionType set to Ph-Ph.
Calculation of zero sequence requires GRPxN input to be connected.
•
Negation setting inverts (reverse) the polarity of the analog input signal. It is
recommended that use of this setting is done with care, mistake in setting may
lead to maloperation of directional functions.
Frequency adaptivity
SMAI function performs DFT calculations for obtaining various electrical
parameters. DFT uses some reference frequency for performing calculations. For
most of the cases, these calculations are done using a fixed DFT reference based on
system frequency. However, if the frequency of the network is expected to vary more
than 2 Hz from the nominal frequency, more accurate DFT results can be obtained if
the adaptive DFT is used. This means that the frequency of the network is tracked and
the DFT calculation is adapted according to that.
DFTRefExtOut and DFTReference need to be set appropriately for adaptive DFT
calculations.
DFTRefExtOut: Setting valid only for the instance of function block SMAI_20_1. It
decides the reference block for external output SPFCOUT.
DFTReference: Reference DFT for the block. This setting decides DFT reference for
DFT calculations. DFTReference set to InternalDFTRef uses fixed DFT reference
based on the set system frequency. DFTReference set to DFTRefGrpX uses DFT
reference from the selected group block, when own group selected adaptive DFT
reference will be used based on the calculated signal frequency from own group.
DFTReference set to External DFT Ref will use reference based on input signal
DFTSPFC.
Settings DFTRefExtOut and DFTReference shall be set to default
value InternalDFTRef if no VT inputs are available. However, if it is
necessary to use frequency adaptive DFT (DFTReference set to other
than default, referring current measuring SMAI) when no voltages are
available, note that the MinValFreqMeas setting is still set in
reference to UBase (of the selected GBASVAL group). This means
that the minimum level for the current amplitude is based on UBase.
For example, if UBase is 20000, the resulting minimum amplitude for
current is 20000 * 10% = 2000.
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 (GBASVAL:n, where 1<n<6).
1MRK 505 288-UEN A
Technical manual
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