7PG21 Solkor Rf Description of Operation
X
D3
Ra
D4
Y
Rp
+
-
D
W
Z
C
B
A
D5
-
+
O
P
R
A
B
C
X
Y
W
Z
D
O
P
a
Rp
Ra
Figure 14 Single End Fed fault Rf mode, positive half cycle
W
X
Y
B
C
A
D
Z
O
P
B
D7
Ra
D8
C
Rp
+
-
Z
A
D
Y
X
W
D1
-
+
O
P
Ra
Rp
Ra
Figure 15 Single End Fed fault Rf mode, negative half cycle
The single end fed internal fault conditions configure the circuit in a similar way to the double end fed internal fault
but only one summation transformer has any output. Thus the other summation transformer acts only as an
equalising transformer, re-circulating current through the measuring element as indicated in
Figure 14 & Figure
15. The voltage distribution shows diagrammatically how, in each half cycle, the measuring elements are
energised via R
a
at the energised end and the action of the remote end summation transformer re-circulating
current via the polarising diodes D4 on one half-cycle and D8 on the other half-cycle.
©2011 Siemens Protection Devices Limited
Chapter 1 Page 12 of 13
