ABB REL 356 Current Differential Protection
4-10
Measuring Elements and Operational Logic
Figure 4-8. Mho Characteristic for Phase to Ground Faults
Three Phase
Three phase fault detection is accomplished by the logic operation of one of the three ground units plus the 3
F
F output
from the phase selector. However, for a three phase fault condition, the computation of the distance units will be:
OP = V
XG
- I
X
Z
P
REF = V
Q
Where
V
Q
= V
CB
for phase A
V
AC
for phase B
V
BA
for phase C
V
XG
= V
AG
, V
BG
or V
CG
I
X
= I
A
, I
B
or I
C
Z
P
= zone reach setting in secondary ohms
Summary of Contents for REL 356
Page 23: ...ABB REL 356 Current Differential Protection 1 10 Product Overview and Specifications ...
Page 83: ...ABB REL 356 Current Differential Protection 3 36 Settings and Application ...
Page 127: ...ABB REL 356 Current Differential Protection 5 28 Testing ...
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