Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
169
Figure 2-68 Phasor diagram of the MHO characteristic measured values
For each distance zone an MHO characteristic can be defined by means of the parameter Z
r
. For each zone it
may also be determined whether it operates forwards or reverse. In reverse direction the MHO characteristic
is mirrored in the origin of the coordinate system. As soon as the fault impedance of any loop is confidently
measured inside the MHO characteristic of a distance zone, the affected loop is designated as „picked up“. The
loop information is also converted to phase-segregated information. Another condition for pickup is that the dis-
tance protection may not be blocked or switched off completely. Figure 2-69 shows these conditions.
The zones and phases of such a valid pickup, e.g. „Dis. Z1 L1“ for zone Z1 and phase L1 are processed by the
zone logic and the supplementary functions (e.g. teleprotection logic).
Figure 2-69 Release logic of a zone (example for Z1)
*) forward and reverse affect only the measured values, not the logic
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