ABB Relion 670 Series Applications Manual page 81

1MRK 511 358-UUS A
Where:
1)
2)
3)
4)
5)
Another alternative is to have the star point of the three-phase CT set as shown in the figure
below:
Application manual
The drawing shows how to connect three individual phase currents from a wye connected three-phase
CT set to the three CT inputs of the IED.
The current inputs are located in the TRM. It shall be noted that for all these current inputs the following
setting values shall be entered for the example shown in Figure25.
'
• CTprim=600A
• CTsec=5A
• CTStarPoint=ToObject
Inside the IED only the ratio of the first two parameters is used. The third parameter
(CTStarPoint=ToObject) as set in this example causes no change on the measured currents. In other
words, currents are already measured towards the protected object.
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.
Section 4
Analog inputs
75