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

Appendix
A.4 Current Transformer Requirements
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

Class accuracy

Table A-2
Neutral point
Function directional
Function non-directional
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").
426
Minimum required class accuracy depending on neutral grounding and function operating prin-
ciple
isolated
Class 1
Class 3
resonant-grounded
Class 1
Class 1
E50417-G1140-C344-A4, Release date 08.2010
60 / 1
FS = 10
1.2 VA
≤ 1.2 VA (≤ 1.2 Ω)
≤ 0.4 VA (≤ 0.4 Ω)
high-resistance ground-
ed
Class 1
Class 3
SIPROTEC, 7SK80, Manual