ABB RET670 Applications Manual page 40

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Section 3
IED application
34
Setting of current channels
The direction of a current to the IED is depending on the connection of the CT. Unless
indicated otherwise, the main CTs are supposed to be Wye (star) connected and can be
connected with the grounding point to the object or from the object. This information
must be set in the IED. The convention of the directionality is defined as follows: A
positive value of current, power, and so on means that the quantity has the direction
into the object and a negative value means direction out from the object. For
directional functions the direction into the object is defined as Forward and the
direction out from the object is defined as Reverse. See figure
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 1.
Definition of direction
for directional functions
Reverse
Forward
e.g. P, Q, I
Measured quantity is
positive when flowing
towards the object
Set parameter
CT_WyePoint
Correct Setting is
"ToObject"
ANSI05000456 V1 EN
Figure 1:
Internal convention of the directionality in the IED
With correct setting of the primary CT direction, CT_WyePoint set to FromObject or
ToObject, a positive quantities always flowing towards the object and a direction
defined as Forward always is looking towards the object. The following examples
show the principle.
Example 1
Two IEDs used for protection of two objects.
Protected Object
Line, transformer, etc
Measured quantity is
positive when flowing
1MRK504116-UUS C
1
Definition of direction
for directional functions
Forward
Reverse
e.g. P, Q, I
towards the object
Set parameter
CT_WyePoint
Correct Setting is
"FromObject"
en05000456_ansi.vsd
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