Siemens 7SJ82 Manual page 874

Protection and Automation Functions
6.43 Restricted Ground-Fault Protection
Protection of an Auto Transformer
[dwsptran-170712-01.tif, 1, en_US]
Figure 6-279
Use the highest side rated current with the auto transformer for normalization. In the example
the measuring point is M2 (230 kV side). For this side, a rated current of 500 MVA/(√(3) · 230 kV) = 1255 A
results. The primary transformer rated current is 1500 A. With this, you can estimate the minimum permissible
pickup value.
[foscwe01-170712-01.tif, 1, en_US]
Siemens recommends a setting value of 0.2 I/Irated,S.
•
Recommended setting value (_:103) Threshold = 0.2 I/Irated,S
874
Activation and Application Example of an Auto Transformer (500 MVA: 400 kV, 230 kV;
125 MVA: 34.5 kV)
(Figure
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
6-279),