IEC11000278_1_en.vsd
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Z1
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IEC11000278 V1 EN
Figure 65: Combined impedance characteristic
Setting of zone 1
The different errors mentioned earlier usually require a limitation of the underreaching
zone (normally zone 1) to 75 - 90% of the protected line.
In case of parallel lines, consider the influence of the mutual coupling according to section
"Parallel line application with mutual coupling" and select the case(s) that are valid in the
particular application. By proper setting it is possible to compensate for the cases when the
parallel line is in operation, out of service and not grounded and out of service and
grounded in both ends. The setting of ground-fault reach should be selected to be <95%
also when parallel line is out of service and grounded at both ends (worst case).
Setting of overreaching zone
The first overreaching zone (normally zone 2) must detect faults on the whole protected
line. Considering the different errors that might influence the measurement in the same
way as for zone 1, it is necessary to increase the reach of the overreaching zone to at least
120% of the protected line. The zone 2 reach can be even higher if the fault infeed from
adjacent lines at remote end is considerable higher than the fault current at the IED
location.
Section 6 1MRK 506 334-UUS A
Impedance protection
132
Application manual
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