•
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
Section 17
1MRK 502 048-UUS A
Basic IED functions
692
Technical manual
