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.
60 / 1
Accuracy limiting factor FS = 10
Power 1 to 4 times the connected burden (device
input plus infeeds)
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
Minimum required class accuracy depending on neutral grounding and function operating
principle
Starpoint isolated compensated high-resistance grounded
Function directional Class 1 Class 1 Class 1
Function non-directional Class 3 Class 1 Class 3
Note that the class accuracy according to IEC 61869-2 below 5% I
rated
(< 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% I
rated
) (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).
D.3
Current Transformer Requirements
D.3 Cable core balance current transformer
458 SIPROTEC 4, 7SJ80, Manual
E50417-G1140-C343-A8, Edition 12.2017
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