that the SMAI function will always calculate the residual sum of current/voltage if the input GRPxN
is not connected in SMT. Applications with a few exceptions shall always be connected to AI3P.
21.9.5.1 Frequency values
GUID-B494B93C-B5AA-4FD6-8080-8611C34C2AD8 v5
The SMAI function includes a functionality based on the level of positive sequence voltage,
MinValFreqMeas
, to validate if the frequency measurement is valid or not. If the positive sequence
voltage is lower than
MinValFreqMeas
, the function freezes the frequency output value for 500 ms
and after that the frequency output is set to the nominal value. A signal is available for the SMAI
function to prevent operation due to non-valid frequency values.
MinValFreqMeas
is set as % of
VBase
/√3
If SMAI setting
ConnectionType
is
Ph-Ph
, at least two of the inputs GRPx_A, GRPx_B and GRPx_C,
where 1≤x≤12, must be connected in order to calculate the positive sequence voltage. Note that
phase to phase inputs shall always be connected as follows: A-B to GRPxA, B-C to GRPxB, C-A to
GRPxC. If SMAI setting
ConnectionType
is
Ph-N
, all three inputs GRPx_A, GRPx_B and GRPx_C must
be connected in order to calculate the positive sequence voltage.
If only one phase-phase voltage is available and SMAI setting
ConnectionType
is
Ph-Ph
, the user is
advised to connect two (not three) of the inputs GRPx_A, GRPx_B and GRPx_C to the same voltage
input as shown in figure
640 to make SMAI calculate a positive sequence voltage.
SMAI1
BLOCK
DFTSPFC
REVROT
^GRP1_A
^GRP1_B
^GRP1_C
^GRP1_N
SPFC OUT
G1AI3P
G1AI1
G1AI2
G1AI4
G1N
NEUTRAL
PHASEC
PHASEB
PHASEA
VAB
SAPTOF
V3P*
BLOCK
BLKTRIP
TRIP
PICK UP
BLKDMAGN
FREQ
TRM_40.CH7(U)
SAPTO F(1)_TRIP
ANSI10000060-1-en.vsdx
ANSI10000060 V1 EN-US
Figure 640: Connection example
The above described scenario does not work if SMAI setting
ConnectionType
is
Ph-
N
. If only one phase-ground voltage is available, the same type of connection can
be used but the SMAI
ConnectionType
setting must still be
Ph-Ph
and this has to be
accounted for when setting
MinValFreqMeas
. If SMAI setting
ConnectionType
is
Ph-
N
and the same voltage is connected to all three SMAI inputs, the positive
sequence voltage will be zero and the frequency functions will not work properly.
The outputs from the above configured SMAI block shall only be used for
Overfrequency protection (SAPTOF, 81), Underfrequency protection (SAPTUF, 81)
and Rate-of-change frequency protection (SAPFRC, 81) due to that all other
information except frequency and positive sequence voltage might be wrongly
calculated.
Section 21 1MRK 502 066-UUS B
Basic IED functions
1268
Technical manual
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