ABB ret650, Applications Manual, Page: 100 / 392

• 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 v10
The most common application is on a solidly earthed transformer winding. The
connection is shown in Figure
34 .
IEC09000109-4-EN.vsd
REFPDIF
I3PW1CT1
I3P
IdN/I
Protected
winding
IEC09000109-4-EN V2 EN-US
Figure 34: Connection of the low impedance Restricted earth fault function
REFPDIF for a directly (solidly) earthed transformer winding
6.2.2.2 Transformer winding, earthed through zig-zag earthing transformer
M13048-8 v10
A common application is for low reactance earthed transformer where the earthing
is through separate zig-zag earthing transformers. The fault current is then limited
to typical 800 to 2000 A for each transformer. The connection for this application
is shown in figure
35 .
Section 6
1MRK 504 169-UEN A
Differential protection
94 Transformer protection RET650 2.2 IEC
Application manual