Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
Z
SL
(I
eq
-I
a
1)
I
eq
Z
set
F
I
F
R
F
V
a
1
Figure 9-1. MHO Phase-Ground Characteristic (I)
Figure 9-1 shows a ground fault MHO characteristic at the inception of a fault. With the voltage
memory feature, the positive sequence voltage two cycles prior to the fault is used to polarize the
MHO characteristic. The diameter of the characteristic is increased by the impedance:
1
(
)
LS
eq
Z
I
I
⋅
−
Figure 9-2 shows a ground fault Mho characteristic for a reverse fault. This characteristic demonstrates
a displacement that is defined by the vector:
1
(
) (
L
LS
eq
)
Z
Z
I
I
+
⋅
−
August 1, 2009
9-3
973.334.3100
