ABB RED650, Applications Manual

Page: 417 / 454

DFTReference : Reference DFT for the SMAI block use.
These DFT reference block settings decide DFT reference for DFT calculations.
The setting
InternalDFTRef will use fixed DFT reference based on set system
frequency. DFTRefGrp(n) will use DFT reference from the selected group block,
when own group is selected, an adaptive DFT reference will be used based on
calculated signal frequency from own group. The setting
ExternalDFTRef will use
reference based on what is connected to input DFTSPFC.
The setting ConnectionType : Connection type for that specific instance (n) of the
SMAI (if it is Ph-N or Ph-Ph ). Depending on connection type setting the not
connected Ph-N or Ph-Ph outputs will be calculated as long as they are possible to
calculate. E.g. at Ph-Ph connection L1, L2 and L3 will be calculated for use in
symmetrical situations. If N component should be used respectively the phase
component during faults I
N
/U
N
must be connected to input 4.
Negation : If the user wants to negate the 3ph signal, it is possible to choose to
negate only the phase signals Negate3Ph , only the neutral signal NegateN or both
NeN . negation means rotation with 180° of the vectors.
GlobalBaseSel : Selects the global base value group used by the function to define
( IBase ), ( UBase ) and ( SBase ).
MinValFreqMeas : The minimum value of the voltage for which the frequency is
calculated, expressed as percent of UBase (for each instance n).
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
1MRK 505 393-UEN B
Section 21
Basic IED functions
Line differential protection RED650 2.2 IEC 411
Application manual