Cable Core Balance Current Transformer - Siemens siprotec SJ62 User Manual

A Appendix
A.4.3

Cable core balance current transformer

General
Requirements to
the cable core
balance current
transformer ac-
cording to
IEC 60044-1 and
IEC61869-2
Class accuracy
629
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 standards IEC 60044-1 and
IEC61869-2.
Transformation ratio, typical
It may be necessary to select a different transformation ratio to
suit the specific power system and thus the corresponding
amount of the maximum ground fault current.
Accuracy limiting factor
Power
Notes concerning the power:
The burden of the sensitive ground-current input is very low (0.05 VA or 0.1 VA). Thus, an un-
derburden of more than factor 4 is probable. In this case, clarify the suitability of the class ac-
curacy concerning an important underburden with the transformer manufacturer. If necessary,
request the accuracy for the range from 0 VA to the rated burden. This specification is then
outside the standard, but in practice, it is possible in most cases.
(Relevant standard: IEC 61869-2, Chapter 5.6.201.4 Extended burden range. There, the range
1 VA to rated burden is specified for rated burdens smaller than 15 VA.)
Table A-2 Minimum required class accuracy depending on neutral grounding and function
operating principle
Starpoint isolated
Function direc- Class 1
tional
Function non-di- Class 3
rectional
Note that the class accuracy according to IEC 61869-2 below 5% Irated (< 50 mA
secondary) is not defined in general. For very sensitive directional measurements,
Siemens recommends the classes 0.5S or 0.1S that define the class accuracy via an
extended current range (up to 1% Irated) (see chapter 5.6.201.5, IEC 61869-2).
Another possibility is to correct the phase-angle error of the transformer on the device,
if this error is known (see function description Sensitive ground-fault detection).
compensated high-resis-
tance grounded
Class 1 Class 1
Class 1 Class 3
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
60 / 1
FS = 10
1 to 4 times the connected
burden (device input plus
infeeds)