Class Conversion; Core Balance Current Transformer; General; Requirements - Siemens SIPROTEC 7SD80 Manual

A.4.3

Class Conversion

Table A-1 Conversion into other classes
British Standard BS 3938
ANSI/IEEE C 57.13, Class C
Note
Detailed information on the transformer design is available on the Internet. (www.siprotec.de)
A.4.4

Core Balance Current Transformer

General

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

Requirements

Maximum difference of the primary rated currents of the core balance current
transformer:
Select the primary rated current of the core balance current transformer so that
ground current flowing in the ground fault of the subnetwork is transmitted by the
core balance current transformer.
Transmission ratio, typical
Depending on the specific power system and the magnitude of the maximum
ground fault current, a different ratio may have to be selected.
Overcurrent limiting factor
Minimum power
Maximum connected burden
– For secondary current thresholds ≥ 20 mA
– For secondary current thresholds < 20 mA
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
= 5 A (typical value)
I
sn
with
V Knee-point voltage
k
R Internal burden
Ct
R Rated burden
B
I Secondary rated transformer current
sn
K Rated overcurrent factor
SSC
V sec. terminal voltage at 20 I
s.t.max
Appendix
A.4 Current Transformer Requirements
pn
0.33 ≥ I
/ I
pn-local pn-remote
60 / 1
FS = 10
1.2 VA
≤ 1.2 VA (≤ 1.2 Ω)
≤ 0.4 VA (≤ 0.4 Ω)
≤ 3
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