Discriminative criteria
We define the R
CT
as the ratio of ||I
P
os
+I
Neg
|| to ||I
Pos
-I
Neg
||:
CT
Pos Neg
Pos Neg
R
I I
I I
n n
n n
=
+
−
|| ( ) ( )||
|| ( ) ( )||
The discriminative criteria is presented below:
Where, Rset is the internal preset value.
The CT saturation is determined on a per phase basis. Ther
efore, the same calculation will be carried out for all 3
phases.
Example
In the example below, the current waveform based on 2-ends application. the current measured at local ends is
blue colour; the current measured at remote ends is red colour. This waveform is an evolving fault from external to
internal fault.
Figure 39: Original current waveforms
The example below shows the output of the calculation for Ipos and Ineg.
Chapter 6 - Current Differential Protection P54A/B/C/E
110 P54xMED-TM-EN-1
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