2 RECOMMENDED CT CLASSES
You can use Class X current transformers with a knee point voltage greater or equal to that calculated. You can
also use class 5P protection CT. These have a knee-point voltage equivalent, which can be approximated from the
following calculations:
V
k
= (VA
´
ALF)/I
n
+ (R
CT
´
ALF
´
I
n
)
where:
● V
k
= Knee-point voltage
● VA = Voltampere burden rating
● ALF = Accuracy limit factor
● I
n
= CT nominal secondary current
● R
CT
= CT resistance
Chapter 16 - Current Transformer Requirements P543i/P545i
420 P54x1i-TM-EN-1
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