ABB REB670 Series - Relationships between setting parameter Base Current, CT rated primary current and minimum pickup of a protection IED

Protected Object
L1 L2 L3
IED
INP
INS
INS
2
IEC11000029-4-en.vsdx
4
3
CT 1000/1
a)
b)
(+)
(+)
(-)
(-)
(+)
(-)
1
SMAI2
BLOCK
REVROT
^GRP2L1
^GRP2L2
^GRP2L3
^GRP2N
AI3P
AI1
AI2
AI3
AI4
AIN
IEC11000029 V4 EN-US
Figure 25: Connections for single-phase CT input
Where:
1) shows how to connect single-phase CT input in the IED.
2) is TRM where these current inputs are located. It shall be noted that for all these current inputs
the following setting values shall be entered.
For connection (a) shown in Fgure 25:
CTprim = 1000 A
CTsec = 1A
CTStarPoint = ToObject
For connection (b) shown in Figure 25:
CTprim = 1000 A
CTsec = 1A
CTStarPoint = FromObject
3) shows the connection made in SMT tool, which connect this CT input to the fourth input channel
of the preprocessing function block 4).
4) is a Preprocessing block that has the task to digitally filter the connected analog inputs and
calculate values. The calculated values are then available for all built-in protection and control
functions within the IED, which are connected to this preprocessing function block.
If frequency tracking and compensation is required (this feature is typically required only for
IEDs installed in the power plants) then the setting parameters DFTReference shall be set
accordingly.
4.2.3 Relationships between setting parameter Base Current, CT
rated primary current and minimum pickup of a protection IED
GUID-8EB19363-9178-4F04-A6AC-AF0C2F99C5AB v1
Note that for all line protection applications (e.g. distance protection or line differential
protection) the parameter Base Current (i.e. IBase setting in the IED) used by the relevant
protection function, shall always be set equal to the largest rated CT primary current among all
CTs involved in the protection scheme. The rated CT primary current value is set as parameter
CTPrim under the IED TRM settings.
For all other protection applications (e.g. generator, shunt reactor, shunt capacitor and
transformer protection) it is typically desirable to set
IBase parameter equal to the rated
current of the protected object. However this is only recommended to do if the rated current
of the protected object is within the range of 40% to 120% of the selected CT rated primary
current. If for any reason (e.g. high maximum short circuit current) the rated current of the
1MRK 505 370-UEN D Section 4
Analog inputs
Busbar protection REB670 73
Application manual