ABB RES670 Applications Manual page 350

Section 22
Basic IED functions
344
Settings DFTRefExtOut and DFTReference shall be set to default
value InternalDFTRef if no VT inputs are available.
Even if the user sets the AnalogInputType of a SMAI block to
"Current", the MinValFreqMeas is still visible. However, using the
current channel values as base for frequency measurement is not
recommendable for a number of reasons, not last among them
being the low level of currents that one can have in normal
operating conditions.
Examples of adaptive frequency tracking
Preprocessing block shall only be used to feed functions within the
same execution cycles (e.g. use preprocessing block with cycle 1 to
feed transformer differential protection). The only exceptions are
measurement functions (CVMMXN, CMMXU,VMMXU, etc.)
which shall be fed by preprocessing blocks with cycle 8.
When two or more preprocessing blocks are used to feed one
protection function (e.g. over-power function GOPPDOP), it is of
outmost importance that parameter setting DFTReference has the
same set value for all of the preprocessing blocks involved
1MRK 511 407-UEN C
Phasor measurement unit RES670 2.2 IEC
Application manual