In the example in figure 14 case everything is done in a similar way as in the above described
example (figure 13). The only difference is the setting of the parameter
CTStarPoint
of the
used current inputs on the TRM (item 2 in the figure):
•
CTprim
=600A
•
CTsec
=5A
•
CTStarPoint
=FromObject
Inside the IED only the ratio of the first two parameters is used. The third parameter as set in
this example will negate the measured currents in order to ensure that the currents are
measured towards the protected object within the IED.
A third alternative is to have the residual/neutral current from the three-phase CT set
connected to the IED as shown in the figure below.
L1
IL1
IL2
IL3
L2 L3
Protected Object
CT 800/1
Star Connected
IL1
IL2
IL3
IN
IED
1
3
4
2
5
IEC06000644-4-en.vsdx
6
SMAI2
BLOCK
REVROT
^GRP2L1
^GRP2L2
^GRP2L3
^GRP2N
AI3P
AI1
AI2
AI3
AI4
AIN
IEC06000644 V4 EN-US
Figure 15: Star connected three-phase CT set with its star point away from the protected object and
the residual/neutral current connected to the IED
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) shows how to connect residual/neutral current from the three-phase CT set to the fourth inputs in
the IED. It shall be noted that if this connection is not made, the IED will still calculate this current
internally by vectorial summation of the three individual phase currents.
Table continues on next page
1MRK 511 358-UEN A Section 4
Analog inputs
61
Application manual
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