Siemens siprotec 7SD5 User Manual page 155

If the short-circuit is located before the capacitor, from the relay location (current trans-
former) in reverse direction, the zeniths of the MHO characteristic are shifted to the
other direction (Figure 2-52c). A correct determination of the direction is thus also
ensured in this case.
Figure 2-52
Assignment to Trip- The assignment of measured values to the tripping zones of the MHO characteristic
is done for each zone by determining the angles between two differential phasors ∆Z
ping Zones and
and ∆Z
Zone Pickup
zeniths of the circle diameter and the fault impedance. The zenith Z
the set value for the zone under consideration (Z
the zenith kZ
phasors are
∆Z
∆Z
In the limiting case, Z
between the two difference phasors is 90° (Thales-theorem). Inside the characteristic
the angle is greater than 90° and outside the circle it is less than 90°.
7SD5 Manual
C53000-G1176-C169-1
Polarized MHO characteristic for series-compensated lines
(Figure 2-53). These phasors result from the difference between the two
2
corresponds to the polarizing magnitude. Therefore the difference
V
= Z – Z
1 F r
= Z – k · Z
2 F S
is located on the perimeter of the circle. In this case the angle
F
2.5 Distance Protection
corresponds to
r
and ϕ
as shown in Figure 2-48),
r MHO
1
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