Figure 57: Mho expansion – forward fault
The Mho expansion associated with forward faults is as follows:
Mho Expansion = Z
S.
p/(1 +p)
where Z
S
is the impedance of the source behind the relaying point.
Using the source and line impedances is a simple way of representing the Mho expansion. The protection
algorithm does not calculate Z
S
internally, it only deals with the signals S
1
and S
2
provided to the Mho
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
S
as follows:
Z
S
= (V
mem
- V)/I
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:
P543i/P545i Chapter 7 - Distance Protection
P54x1i-TM-EN-1 145
To Next Page
Loading...
Need help?
General
