Offset Mho Characteristic For Earth Faults; Figure 37: Offset Mho Characteristics - Impedance Domain - GE MiCOM P40 Technical Manual

Chapter 7 - Distance Protection
Then if healthy phase currents are much less then the current of the faulty phase and the mutual compensation is
disabled:
@ I
I
N ph
so that
@ Z(1 + k
Z
replica
Thus the Z plane representation of the characteristic becomes static.
LP
3.1.4

OFFSET MHO CHARACTERISTIC FOR EARTH FAULTS

The diagram below illustrates how the Offset Mho characteristic for earth-fault distance protection is created in
the impedance domain.
V02713
Figure 37: Offset Mho characteristics – impedance domain
The two signals provided to the comparator are:
S = V - I.Z'
1
S = V - I.Z
2
Operation occurs when the angle between the signals is greater than 90°.
The following diagram below how the Offset Mho characteristic for earth-fault distance protection translates to
the loop impedance domain.
114
)
ZN

j
Z 
Z
-plane
X
1
Z
V I

V I Z
90°


V I Z

R
P446SV-TM-EN-1
P446SV