Siemens 7PG21 Solkor Rf - Figure 8 through Fault Rf Mode, Positive Half Cycle

7PG21 Solkor Rf Description of Operation
BC
A
XY
W
Z
D
O P
D3
R
a
D4
X
Y
R
p
+
-
D2
D
-
+
W Z
C
B
A
D5
+
-
-
+
O
P
R
a
D7
D8
R
p
Figure 8 Through fault Rf mode, positive half cycle
D4
R
a
D3
Y
X
R
p
+
-
D1
A
-
+
ZW
B
C
D
D5
+
-
-
+
O
P
R
a
D8
D7
R
p
CB
D
YX
Z
W
A
PO
Figure 9 Through fault Rf mode, negative half cycle
Considering now the equivalent Solkor Rf circuit with 1000 ohms in each leg of the pilots as shown in Figure 8.
the voltage distribution shows that the bias voltage across the polarising diodes (D3, D4, D7 and D8) with this
arrangement are effectively identical with the minimum values obtained in the Solkor R arrangement. In other
words, the balance of the full wave comparison gives the same value of bias for each polarity of half-cycle
.
©2011 Siemens Protection Devices Limited Chapter 1 Page 9 of 13