Figure 53: Directional Mho Element Construction - Impedance Domain - GE MiCOM P40 Agile Technical Manual

P543i/P545i
Z
1

j X
Z
V02712
Figure 53: Directional Mho element construction – impedance domain
The two signals provided to the comparator are:
S = V
1
S = V - IZ
2
where (for an A-N fault for example) with residual compensation applied:
V = V
A
I = I + k .I
A ZN N
where k = (Z - Z ) / 3Z
ZN 0 1
and if mutual compensation is applied:
I = I + k .I + k
A ZN N
where k = 3Z / 3Z and is defined by two settings: kZm Mutual Set and kZm Mutual Angle.
ZM M 1
Operation occurs when the angle between the signals is greater than 90°.
To obtain a Z -plane representation in the directional Mho element construction, V is replaced with V
LP
replaced with I + k .I
ph ZN N
mutual current compensation).
The two signals provided to the comparator in this case are:
S = V
1 ph
S = V - I .Z(1+k
2 ph ph
We can define a replica impedance reach, Z
Z = Z(1+k
replica ZN
or if mutual compensation is applied:
P54x1i-TM-EN-1
Plane

V I
90°

V I
and is defined by two settings: kZN Res Comp and KZN Res Angle.
1
.I
ZM M
, where V and I are the faulty phase voltage and current respectively (assuming no
ph ph
.I /I )
ZN N ph
replica
.I /I )
N ph
Z
Z
j 
X
Z
Z
R
, as:
Chapter 7 - Distance Protection
Plane
LP
 
k I I
ZN N ph
V
ph
Z
replica
90°

R
V I
ph ph

I Z
ph replica
and I is
ph
141