Hitachi Relion 670 Series Applications Manual page 55

1MRK511407-UUS Rev. N
Where:
1)
2)
3)
4)
5)
Another alternative is to have the wye point of the three-phase CT set as shown in figure 13:
Phasor measurement unit RES670
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 Figure 12.
• 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.
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 A, B, C 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 GRP_A, GRP_B and GRP_C. If GRP2N is connected, the data reflects the measured
value of GRP2N.
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Section 4
Analog inputs
49