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Figure 2-64
Properties of the MHO Characteristic
As the quadrature or memorized voltage (without load transfer) equals the corresponding generator voltage E
and does not change after fault inception (refer also to Figure 2-65), the lower zenith is shifted in the impedance
diagram by the polarization quantity k·Z
the fault location F
the reverse direction. All fault locations right up to the device mounting location (current transformers) are
clearly inside the MHO characteristic (Figure 2-65b). If the current is reversed, the zenith of the circle diameter
changes abruptly (Figure 2-65c). A reversed current I
now flows via the measuring location (current transformer) . The zenith Z
lower boundary of the circle diameter. In conjunction with load transport via the line, the zenith vector may ad-
ditionally be rotated by the load angle.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
Polarized MHO characteristic
S1
(Figure 2-65a), the short-circuit is in the forward direction and the source impedance is in
1
= k·E
/I
. The upper zenith is still defined by the setting value Z
1
1
which is determined by the source impedance Z
2
2.5 Distance Protection
remains unchanged; it now is the
r
Functions
. For
r
+ Z
S2
L
165
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