Where:
1)
The drawing shows how to connect three individual phase currents from a star connected
three-phase CT set to the three CT inputs of the IED.
2)
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 Figure
•
CTprim=600A
•
CTsec=5A
•
CTStarPoint=ToObject
Ratio of the first two parameters is only used inside the IED. 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.
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. 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.
Another alternative is to have the star point of the three-phase CT set as shown in
Figure
:
1MRK 505 388-UEN B
Section 4
Analog inputs
Busbar protection REB650 2.2 IEC
43
Application manual
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