ABB Relion REC670 Applications Manual page 66

Section 4
Analog inputs
3)
4)
5)
Another alternative is to have the star point of the three-phase CT set as shown in the figure
below:
L1
CT 800/1
Star Connected
Protected Object
IEC11000026 V4 EN-US
Figure 14: Star connected three-phase CT set with its star point away from the protected object
60
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.
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).
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. In this example GRP2N is not connected so this data is calculated by the
preprocessing function block on the basis of the inputs GRPL1, GRPL2 and GRPL3. If GRP2N is
connected, the data reflects the measured value of GRP2N.
L2 L3
IN
IL3
IL2
IL1
IED
2
1
3
1MRK 511 358-UEN A
4
SMAI2
BLOCK AI3P
REVROT AI1
5
^GRP2L1 AI2
^GRP2L2 AI3
^GRP2L3 AI4
^GRP2N AI N
IEC11000026-4-en.vsdx
Application manual