ABB RET650 Technical Manual page 592

Section 17
Basic IED functions
586
• It is not mandatory to connect all the inputs of SMAI function. However, it is very
important that same set of three phase analog signals should be connected to one
SMAI function.
• The sequence of input connected to SMAI function inputs GRPxL1, GRPxL2,
GRPxL3 and GRPxN should normally represent phase L1, phase L2, phase L3
and neutral currents respectively.
• It is possible to connect analog signals available as Ph-N or Ph-Ph to SMAI.
ConnectionType should be set according to the input connected.
• If the GRPxN input is not connected and all three phase-to-earth inputs are
connected, SMAI calculates the neutral input on its own and it is available at the
AI3P and AIN outputs. It is necessary that the ConnectionType should be set to
Ph-N.
• If any two phase-to-earth inputs and neutral currents are connected, SMAI
calculates the remaining third phase-to-neutral input on its own and it is available
at the AI3P output. It is necessary that the ConnectionType should be set to Ph-
N.
• If any two phase-to-phase inputs are connected, SMAI calculates the remaining
third phase-to-phase input on its own. It is necessary that the ConnectionType
should be set to Ph-Ph.
• 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
1MRK 504 135-UEN A
Technical manual