and:
• Z
ADD
= Z
A
+ Z
B
for parallel lines.
• I
A
, I
FA
and U
A
are given in the above table.
• K
N
is calculated automatically according to equation 67.
• Z
A
, Z
B
, Z
L
, Z
0L
and Z
0M
are setting parameters.
For a single line, Z
0M
= 0 and Z
ADD
= 0. Thus, equation
68 applies to both single and
parallel lines.
Equation 68 can be divided into real and imaginary parts:
p
2
p Re K
1
( ) Re K
2
( ) R
F
Re K
3
( ) 0=×–+×–
EQUATION107 V1 EN (Equation 72)
p Im K
1
( ) Im K
2
( ) R
F
Im K
3
( ) 0=× ×–×+× ×–
EQUATION108 V1 EN (Equation 73)
If the imaginary part of K
3
is not zero, R
F
can be solved according to equation 73, and
then inserted to equation 72. According to equation 72, the relative distance to the fault
is solved as the root of a quadratic equation.
Equation 72 gives two different values for the relative distance to the fault as a
solution. A simplified load compensated algorithm, which gives an unequivocal
figure for the relative distance to the fault, is used to establish the value that should be
selected.
If the load compensated algorithms according to the above do not give a reliable
solution, a less accurate, non-compensated impedance model is used to calculate the
relative distance to the fault.
12.14.7.3 The non-compensated impedance model
In the non-compensated impedance model, I
A
line current is used instead of I
FA
fault
current:
EQUATION109 V1 EN (Equation 74)
Where:
I
A
is according to table 411.
The accuracy of the distance-to-fault calculation, using the non-compensated
impedance model, is influenced by the pre-fault load current. So, this method is only
used if the load compensated models do not function.
1MRK 511 287-UEN A Section 12
Monitoring
479
Technical manual
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