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Even if the
AnalogInputType
setting of a SMAI block is set to
Current
, the
MinValFreqMeas
setting is still visible. This means that the minimum
level for current amplitude is based on
VBase
. For example, if
VBase
is
20000, the minimum amplitude for current is 20000 * 10% = 2000. This
has practical affect only if the current measuring SMAI is used as a
frequency reference for the adaptive DFT. This is not recommended, see
the Setting guidelines.
15.9.6
Operation principle
Every SMAI can receive four analog signals (three phases and one neutral value), either
voltage or current. The
AnalogInputType
setting should be set according to the input
connected. The signal received by SMAI is processed internally and in total 244 different
electrical parameters are obtained for example RMS value, peak-to-peak, frequency and
so on. The activation of
BLOCK
input resets all outputs to 0.
SMAI_20 does all the calculation based on nominal 20 samples per line frequency period,
this gives a sample frequency of 1 kHz at 50 Hz nominal line frequency and 1.2 kHz at 60
Hz nominal line frequency.
The output signals
AI1
...
AI4
in SMAI_20_x function block are direct outputs of the
connected input signals
GRPx_A
,
GRPx_B
,
GRPx_C
and
GRPx_N
.
GRPx_N
is always
the neutral current. If
GRPx_N
is not connected, the output
AI4
is zero. The
AIN
output
is the calculated residual quantity, obtained as a sum of inputs
GRPx_A
,
GRPx_B
and
GRPx_C
but is equal to output
AI4
if
GRPx_N
is connected. The outputs signal
AI1
,
AI2
,
AI3
and
AIN
are normally connected to the analog disturbance recorder.
The SMAI function block always calculates the residual quantities in case
only the three phases (Ph-N) are connected (
GRPx_N
input not used).
The output signal
AI3P
in the SMAI function block is a group output signal containing
all processed electrical information from inputs
GRPx_A
,
GRPx_B
,
GRPx_C
and
GRPx_N
. Applications with a few exceptions shall always be connected to
AI3P
.
The input signal
REVROT
is used to reverse the phase order.
A few points need to be ensured for SMAI to process the analog signal correctly.
1MRK 511 287-UUS A
Section 15
Basic IED functions
613
Technical manual
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