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2.10
Restricted Earth Fault Protection (optional)
The restricted earth fault protection detects earth faults in power transformers with earthed starpoint. It is also
suitable when a starpoint former is installed within a protected zone of a non-earthed power transformer. A pre-
condition is that a current transformer is installed in the starpoint connection, i.e. between the starpoint and the
earthing electrode. The starpoint CT and the phase CTs define the limits of the protected zone exactly.
2.10.1
Application Examples
Figures 2-130 and 2-131 show two application examples. A prerequisite is that the I4 transformer detects the
starpoint current of the transformer side to be protected.
Figure 2-130
Figure 2-131
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Restricted earth fault protection on an earthed transformer winding
Earth fault differential protection at a delta winding with earthed artificial starpoint
(neutral earthing transformer, zigzag reactor)
2.10 Restricted Earth Fault Protection (optional)
Functions
265
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