Cable Core Balance Current Transformer - Siemens SIPROTEC 4 Manual

Current Transformer Requirements
D.3 Cable core balance current transformer
D.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 standards IEC 60044-1 and IEC61869-2.
Requirements to the cable core balance current transformer according to 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 underburden of
more than factor 4 is probable. In this case, clarify the suitability of the class accuracy concerning an impor-
tant 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.)
Class accuracy
Table D-2
Starpoint
Function directional
Function non-directional
Note that the class accuracy according to IEC 61869-2 below 5% I
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% I
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).
458
Minimum required class accuracy depending on neutral grounding and function operating
principle
isolated
Class 1
Class 3
60 / 1
FS = 10
1 to 4 times the connected burden (device
input plus infeeds)
compensated
Class 1
Class 1
(< 50 mA secondary) is not defined in
rated
) (see chapter 5.6.201.5, IEC 61869-2).
rated
E50417-G1140-C343-A8, Edition 12.2017
high-resistance grounded
Class 1
Class 3
SIPROTEC 4, 7SJ80, Manual