ABB RET670 Applications Manual page 48

Section 3
IED application
42
3) These three connections are the links between the three current inputs and the three input
channels of the preprocessing function block 4). Depending on the type of functions, which
need this current information, more than one preprocessing block might be connected in
parallel to the same three physical CT inputs.
4) The preprocessing block that has the task to digitally filter the connected analog inputs and
calculate:
• fundamental frequency phasors for all three input channels
• harmonic content for all three input channels
• positive, negative and zero sequence quantities by using the fundamental frequency
phasors for the first three input channels (channel one taken as reference for sequence
quantities)
These calculated values are then available for all built-in protection and control functions within
the IED, which are connected to this preprocessing function block. For this application most of
the preprocessing settings can be left to the default values.
If frequency tracking and compensation is required (this feature is typically required only for
IEDs installed in power plants), then the setting parameters DFTReference shall be set
accordingly.
Section SMAI in this manual provides information on adaptive frequency tracking for the signal
matrix for analogue inputs (SMAI).
5) AI3P in the SMAI function block is a grouped signal which contains all the data about the
phases L1, L2, L3 and neutral quantity; in particular the data about fundamental frequency
phasors, harmonic content and positive sequence, negative and zero sequence quantities are
available.
AI1, AI2, AI3, AI4 are the output signals from the SMAI function block which contain the
fundamental frequency phasors and the harmonic content of the corresponding input channels
of the preprocessing function block.
AIN is the signal which contains the fundamental frequency phasors and the harmonic content
of the neutral quantity; this data is calculated by the preprocessing function block on the basis
of the inputs GRPL1, GRPL2 and GRPL3.
Another alternative is to have the star point of the three-phase CT set as shown in the
figure below:
1MRK504116-UUS C
Application manual