P44x/EN AP/Hb
MiCOM P40 Agile P442, P444
(AP) 5-
2.3.1 Convergence Analysis
This analysis is based on the measurements of distance and resistance of the fault. These
measurements are taken on each phase-ground and phase-phase loops (18 loops in total).
They determine the convergence of these loops within a parallelogram-shaped, start-up
characteristic.
D
R
P3037ENa
- R
R
lim
lim
- D
lim
D= X3
d
lim
= X
4
For multi phase fault :
q
= argument of Z
1
(positive sequence impedance)
For single phase fault :
q
= argument of (2 Z
1
+Z
02
)/ 3
for zone 2, etc...
q
= argument of (2 Z
1
+Z
01
)/ 3
for zone 1
L = line length in km or mile s
D3 = Z3/Zd x L = X3
D4 = Zd x L = X4
1
2
Figure 8: Start-up characteristic
Let R
lim
and D
lim
be the limits of the starting characteristic.
The pair of solutions (D
fault
(n-1), R
fault
(n-1)) and (D
fault
(n), R
fault
(n)):
• R
fault
(n-1)< R
lim
, and R
fault
(n)< R
lim
, and R
fault
(n-1) - R
fault
(n)< 10% x R
lim
• D
fault
(n-1)< D
lim
and D
fault
(n) < D
lim
and D
fault
(n-1) - D
fault
(n) < 10% x D
lim
where R
lim
is the resistance limit for the single and multi phase faults. This convergence
requires the equations to be collinear, therefore allowing the terms in D
fault
and R
fault
to be
discriminated.
Theoretically, zone limits are Z3, Z4, +/- R3G-R4G or +/- R3Ph-R4Ph, if zones 3 and 4 are
enabled. The slope of the characteristic mimics the characteristic of the line.
To model the fault current:
• Phase-phase loops: the values (I
A
- I
B
), (I
B
- I
C
), or (I
C
- I
A
) are used.
• Phase-ground loops: (I
A
+ k
0
x 3I
0
), (I
B
+ k
0
x 3I
0
), or (I
C
+ k
0
x 3I
0
) are used.
The results of these algorithms are mainly used as a backup; consequently, the circuit
breaker located at the other end is assumed to be open.
2.3.2 Start-Up
Start-up is initiated when at least one of the six measuring loops converges in the
characteristic (Z
AN
, Z
BN
, Z
CN
, Z
AB
, Z
BC
, Z
CA
).
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