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A restricted earth-fault protection is the fastest and the most sensitive protection, a power
transformer winding can have and will detect faults such as:
•
earth faults in the transformer winding when the network is earthed through an
impedance
•
earth faults in the transformer winding in solidly earthed network when the point of the
fault is close to the winding star point.
The restricted earth-fault protection is not affected, as a differential protection, with the
following power transformer related phenomena:
•
magnetizing inrush currents
•
overexcitation magnetizing currents
•
load tap changer
•
external and internal phase faults which do not involve earth
•
symmetrical overload conditions
Due to its features, REFPDIF is often used as a main protection of the transformer winding for
all faults involving earth.
6.2.2.1
Transformer winding, solidly earthed
M13048-3 v9
The most common application is on a solidly earthed transformer winding. The connection is
shown in figure
.
IEC09000109-4-EN.vsd
REFPDIF
I3PW1CT1
I3P
IdN/I
Protected
winding
IEC09000109-4-EN V2 EN-US
Figure 40: Connection of the low impedance Restricted earth-fault function REFPDIF for
a directly (solidly) earthed transformer winding
1MRK 505 343-UEN B
Section 6
Differential protection
109
Application manual
Summary of Contents for Relion 670 series
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