Appendix
A.4 Current Transformer Requirements
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
614
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
Class accuracy
Table A-2
Minimum required class accuracy depending on neutral grounding and function operating prin-
ciple
For extremely small ground fault currents it may become necessary to correct the angle at the device (see func-
tion description of „sensitive ground fault detection“).
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.
60 / 1
Accuracy limiting factor
FS = 10
Minimum power
1.2 VA
Maximum connected load
– For secondary current threshold values
≥
20 mA
– For secondary current threshold values < 20 mA
≤
1.2 VA (
≤
1.2
Ω
)
≤
0.4 VA (
≤
0.4
Ω
)
Starpoint
isolated
compensated
high-resistance ground-
ed
Function directional
Class 1
Class 1
Class 1
Function non-directional
Class 3
Class 1
Class 3
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