ABB Relion 650 Series Applications Manual page 44

Section 4
Analog inputs
primary current among all CTs involved in the protection scheme. The rated CT primary current
value is set as parameter
For all other protection applications (e.g. 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 protected object is less than 40% of the rated CT primary current,
it is strongly recommended to set the parameter
CT primary current among all CTs involved in the protection scheme and installed on the same
voltage level. This will effectively make the protection scheme less sensitive; however, such
measures are necessary in order to avoid possible problems with loss of the measurement
accuracy in the IED.
Regardless of the applied relationship between the
current, the corresponding minimum pickup of the function on the CT secondary side must always
be verified. It is strongly recommended that the minimum pickup of any instantaneous protection
function (e.g. differential, restricted earth fault, distance, instantaneous overcurrent, etc.) shall
under no circumstances be less than 4% of the used IED CT input rating. This corresponds to
40mA secondary for main CTs with 1A rating and to 200mA secondary for main CTs with 5A rating.
This shall be individually verified for all current inputs involved in the protection scheme.
4.2.3 Setting of current channels
The direction of a current depends on the connection of the CT. Unless indicated otherwise, the
main CTs are supposed to be Wye (star) connected. The IED can be connected with its grounding
point towards the object or away from the object. This information must be set in the IED via the
parameter
the IED algorithms and IED functions, the convention of the directionality is defined as follows:
A positive value of current, power, and so on (forward) means that the quantity has a direction
towards the object. - A negative value of current, power, and so on (reverse) means a direction
away from the object. See figure 8.
Definition of direction
for directional functions
Reverse
Set parameter
CTStarPoint
Correct Setting is
"ToObject"
ANSI05000456 V2 EN-US
Figure 8:
38
CTPrim under the IED TRM settings.
CT_WyePoint , which can be changed between FromObject and ToObject . Internally in
Forward
Protected Object
Line, transformer, etc
e.g. P, Q, I
Measured quantity is
positive when flowing
towards the object
Internal convention of the directionality in the IED
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IBase in the IED to be equal to the largest rated
IBase parameter and the rated CT primary
Definition of direction
for directional functions
Forward Reverse
e.g. P, Q, I
Measured quantity is
positive when flowing
towards the object
Set parameter
CTStarPoint
Correct Setting is
"FromObject"
en05000456-2.vsd
1MRK 505 287-UUS B
SEMOD55055-16 v5
Busbar protection REB650
Application manual