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Note
On long lines with small R/X ratio, care must be taken to ensure that the R reach of the zone settings is at least
about half of the associated X setting. This is especially important for zone Z1 and overreach zone Z1B in order
to achieve the shortest possible tripping times.
Independent Zones Z1 to Z6
By means of the parameter MODE = Forward or Reverse or Non-Directional, each zone can be set (ad-
dress 1601 Op. mode Z1, 1611 Op. mode Z2, 1621 Op. mode Z3, 1631 Op. mode Z4, 1641 Op. mode
Z5 and 1661 Op. mode Z6). This allows any combination of graded zones - forward, reverse or non-direc-
tional -, for example on transformers, generators, or bus couplers. For the fifth and sixth zone, you can addi-
tionally set different reaches for forward and reverse. Zones that are not required are set to Inactive.
The values derived from the grading coordination chart are set for each of the required zones. The setting pa-
rameters are grouped for each zone. For the first zone these are the parameters R(Z1) Ø-Ø (address 1602)
for the R intersection of the polygon applicable to phase-to-phase faults, X(Z1) (address 1603) for the X in-
tersection (reach), RE(Z1) Ø-E (address 1604) for the R intersection applicable to phase-to-earth faults and
delay time settings.
If a fault resistance at the fault location (arc, tower footing etc.) causes a voltage drop in the measured imped-
ance loop, the phase angle difference between this voltage and the measured loop current may shift the deter-
mined fault location in X direction. Parameter 1607 Zone Reduction allows an inclination of the upper limit
of zone Z1 in the 1st quadrant (see Figure 2-52). This prevents spurious pickup of zone Z1 in the presence of
faults outside the protected area. Since a detailed calculation in this context can only apply for one specific
system and fault condition, and a virtually unlimited number of complex calculations would be required to de-
termine the setting, we suggest a simplified but well-proven method here:
Figure 2-61
The voltage drop at the fault location is:
U
= (I
+ I
) · R
F
A
B
If I
and I
have equal phase, then U
A
B
not influence the measured X in the loop, and the Zone Reduction can be set to 0°.
In practice, I
A
. This angle (also called load angle) is therefore used to determine the Zone Reduction angle.
U
and U
A
B
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Equivalent circuit diagram for the recommended angle setting Zone Reduction.
F
and I
F
and I
do not have equal phase; the difference results mostly from the phase difference between
B
have equal phase too. In this case the fault resistance R
A
Functions
2.5 Distance Protection
does
F
157
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