Siemens SIPROTEC 7SJ61, Руководство пользователя, Страница: 393 / 454

Appendix
A.4 Current Transformer Requirements
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008 393
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
)
Neutral isolated compensated high-resistance ground-
ed
Class 3 Class 1 Class 3