•
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
Section 17
1MRK 504 135-UEN A
Basic IED functions
586
Technical manual
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