Appendix
A.4 Current Transformer Requirements
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
613
A.4.2 Class conversion
Table A-1 Conversion into other classes
British Standard BS 3938
ANSI/IEEE C 57.13, class C
I
sNom
= 5 A (typical value)
IEC 60044-6 (transient response), class
TPS
Classes TPX, TPY, TPZ
K≈ 1
K
SSC
≈ K
ALF
Calculation See ChapterA.4.1 Accuracy limiting factors with: K
SSC
≈
n
T
P
depending on power system and specified closing sequence
with
V
k
Knee-point voltage
R
Ct
Internal burden resistance
R
BN
Nominal burden resistance
I
sNom
secondary nominal transformer current
K
ALF
Rated accuracy limiting factor
V
s.t.max
sec. terminal volt. at 20 I
pNom
V
al
sec. magnetization limit voltage
K Dimensioning factor
K
SSC
Factor symmetr. Rated fault current
T
P
Primary time constant
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