1
1
0
0
L
R
L
E
m
Em
U
Z
I
k I
k
I
(compensated)
where,
•
k
0
: zero-sequence compensation factor for Z
0
0
1
/ 3
k
Z
•
k
0m
: zero-sequence compensation factor for the mutual impedance Z0m of double-circuit
line
0
0
1
3
m
m
k
Z
Z
The mutual zero-sequence impedance of a double-circuit line (k
0m
× I
Em
) is only compensated
for the first, second and overreaching zones, and in the latter two cases, only if their direction
of measurement is the same as that of the first zone. In this respect, a reverse measuring zone
is treated in the same manner as an overreaching zone.
The mutual zero-sequence impedance (k
0m
× I
Em
) is not compensated, should I
Em
exceed 1.25 ×
I
E
or the direction of I
Em
not be the same as that of I
E
. This prevents a healthy parallel circuit
from being adversely influenced by a fault relatively close to the relay location of the faulted
circuit.
Assuming a fault between L1 and L2, the impedance of the phase-to-phase loop is calculated
using the equation:
1
2
1 2
1
2
L
L
L L
L
L
U
U
Z
I
I
It is determined almost simultaneously, whether the impedance measured lies within the
characteristic and whether it is in the direction of the first zone and overreaching zone, or in
the direction of the reverse measuring zone. The corresponding tripping and other signals are
processed by the system logic. Tripping of the circuit-breaker, however, only takes place after
a measuring unit has operated twice.
1MRK 505 406-UEN B
Section 5
Bay protection functions
Bay protection functions REB500
59
Technical manual
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