Figure 57: Mho Expansion - Forward Fault - GE MiCOM P40 Agile Technical Manual

P543i/P545i

1
V02716
Figure 57: Mho expansion – forward fault
The Mho expansion associated with forward faults is as follows:
Mho Expansion = Z
where Z is the impedance of the source behind the relaying point.
S
Using the source and line impedances is a simple way of representing the Mho expansion. The protection
algorithm does not calculate Z
comparators. In some cases the source and line impedances are different from their actual values used in various
power system studies. This is mainly due to pre-fault current and the residual compensation for phase-to-ground
loops. To plot an accurate impedance characteristic, calculate the values of Z
Z = (V - V)/I
S mem
Dynamic Mho Contraction for Reverse Faults
The contribution of additional polarizing input creates dynamic Mho contraction for reverse faults and enhances
the directional decision
Referring to the following diagram:
P54x1i-TM-EN-1

j X
p

Z
S

p
p/(1 +p)
S.
internally, it only deals with the signals S
S
Chapter 7 - Distance Protection
Self-polarised
V I
Z
V I
90°

R

V I
1
and S provided to the Mho
1 2
as follows:
S

Z
p

Z
S

p
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