ABB Relion Technical Manual page 698

Section 17
Basic IED functions
692
• 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 GRPx_A, GRPx_B,
GRPx_C and GRPx_N should normally represent phase A, phase B, phase C 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 GRPx_N input is not connected and all three phase-to-ground 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-ground 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 GRPx_x should be connected to SMAI for calculating sequence
components for ConnectionType set to Ph-N.
• At least two inputs GRPx_x should be connected to SMAI for calculating the positive
and negative sequence component for ConnectionType set to Ph-Ph. Calculation of
zero sequence requires GRPx_N 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
1MRK 502 048-UUS A
Technical manual