Class Conversion; Cable Core Balance Current Transformer; General; Requirements - Siemens 7SK80 Manual

A.4.2

Class conversion

Table A-1
British Standard BS 3938
ANSI/IEEE C 57.13, class C
IEC 60044-6 (transient response), class
TPS
Classes TPX, TPY, TPZ
A.4.3

Cable core balance current transformer

General

The requirements to the cable core balance current transformer are determined by the function „sensitive
ground fault detection".
The recommendations are given according to the standard IEC 60044-1.

Requirements

Transformation ratio, typical
It may be necessary to select a different transformation ratio to suit the specific
power system and thus the amount of the maximum ground fault current.
Accuracy limiting factor
Minimum power
Maximum connected load
– For secondary current threshold values ≥ 20 mA
– For secondary current threshold values < 20 mA
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
Conversion into other classes
I = 5 A (typical value)
sNom
K≈ 1
≈ K
K
SSC ALF
Calculation See ChapterA.4.1 Accuracy limiting factors with: K
K
ALF
T depending on power system and specified closing sequence
P
with
V Knee-point voltage
k
R Internal burden resistance
Ct
R Nominal burden resistance
BN
Secondary nominal transformer current
I
sNom
K Rated accuracy limiting factor
ALF
V Sec. terminal voltage at 20 I
s.t.max
V Sec. magnetization limit voltage
al
K Dimensioning factor
K Factor symmetr. Rated fault current
SSC
T Primary time constant
P
A.4 Current Transformer Requirements
pNom
60 / 1
FS = 10
1.2 VA
≤ 1.2 VA (≤ 1.2 Ω)
≤ 0.4 VA (≤ 0.4 Ω)
Appendix
≈
SSC
443