Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
For faults with low positive sequence voltage (less than 10 V), memory voltage is used.
The following table shows the operation and polarization phasors of the Mho characteristic measuring
elements, as well as the applied operating criterion.
Table 9-1. MHO Characteristic
Unit OP POL Criteria
AG
[
0( 0 1)]
Ia I k
ZF Va
+
−
⋅
−
Va1M
BG
[
0( 0 1)]
Ib I k
ZF Vb
+
−
⋅
−
Vb1M
CG
[
0( 0 1)]
Ic I k
ZF Vc
+
−
⋅
−
Vc1M
AB
Iab ZF Vab
⋅
−
Vab1M
BC
90
[arg(
) arg(
)] 90
OP
POL
− ° ≤
−
≤
°
Ibc ZF Vbc
⋅
−
Vbc1M
Ica ZF Vca
⋅
−
Vca1M
CA
Table 9-2. MHO Characteristic Table Definitions
Figure 8-1 shows the phase-to-ground fault Mho characteristics. Due to the polarization used, the
diameter of the characteristic is the vector addition of the adjusted reach and a vector corresponding to
the local source impedance. This effect enables tripping for close in faults with very low voltage. This
displacement has no effect on the directional characteristic. For a reverse fault, the mho characteristic
is displaced in the forward direction.
August 1, 2009
9-2
973.334.3100
