Zs=0
R
jx
Mho, zone4
Mho, zone3
Mho, zone2
Mho, zone1
Offset mho, zone5
IEC09000143_2_en.vsd
X
R
Zs=Z1
Zs=2Z1
IEC09000143 V2 EN
Figure 39:
Mho, offset mho characteristic and the source impedance influence on the mho characteristic
The mho characteristic has a dynamic expansion due to the source impedance. Instead of
crossing the origin as for the mho to the left of figure
, which is only valid where the
source impedance is zero, the crossing point is moved to the coordinates of the negative
source impedance given an expansion of the circle shown to the right of figure
. Z1
denotes the complex positive sequence impedance.
The polarization quantities used for the mho circle are 100% memorized positive
sequence voltages. This will give a somewhat less dynamic expansion of the mho circle
during faults. However, if the source impedance is high, the dynamic expansion of the
mho circle might lower the security of the function too much with high loading and mild
power swing conditions.
Basic operation characteristics
In ZQMPDIS (21), each zone measurement loop characteristic can be set to mho
characteristic by setting
CharPPZx
or
CharPGZx
(where
x
is 1-5 depending on selected
zone). These mho characteristics can be classified into -
Offset
or
Directional
. The
directional mho characteristics can be set to
Non-directional
,
Forward
or
Reverse
by the
setting parameter
DirModeZx
(where
x
is 1-5 depending on selected zone). The offset mho
characteristic can be set to
Forward
or
Reverse
by the setting parameter
MhoCharZx
(where
x
is 1-5 depending on selected zone).
1MRK 506 335-UUS A
Section 6
Impedance protection
109
Technical manual
Содержание REL650 series
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