R
R
X
R
X
R
R
X
R
Forward Reverse Non-directional
(a) (b) (c)
X
X
Rset
Xset
Rset
Xset
X
R
Rset
Xset
(a) and (c) are for Zone 1, Zone 2 and Zone 3-5 when DirModeZ3-5 = Forward.
(b) and (d) are for ZoneRV and Zone 3-5 when DirModeZ3-5 = Reverse
(c) and (f) are for Zone 3-5 when DirModeZ3-5 = Non-Directional
(d)
(e) (f)
Mho Characteristics
Offset Mho Characteristics
1
1
01
3
01
3
Rset R Zx RNZx
Xset X Zx XNZx
X Zx X Zx
XNZx
R Zx R Zx
RNZx
Rset
Xset
Xset
Rset
Rset
Xset
Xset
Rset
Rset
Xset
Xset
Rset
(a)-(f)
For phase-to-phase fault
For phase-to-earth fault
Forward Reverse Non-directional
IEC15000055 V2 EN-US
Figure 154: Mho and offset Mho characteristics
For each zone, the impedance is set in cartesian coordinates (resistance and reactance) which is
the same as for quadrilateral characteristic.
The ZMFPDIS function has only one set of reach setting so the reverse will be the same as for the
forward reach, meaning that the non-directional offset mho characteristic will always be centered
around the origin. In detail, for Zone 1, the resistive and reactance reaches for phase-to-earth fault
and phase-to-phase fault are set individually using the settings
R1PPZ1
,
X1PPZ1
,
R1PEZ1
,
X1PEZ1
,
X0Z1
and
R0Z1
. In Zone 2-5 and Zone RV, the same zone reach settings are used for phase-to-earth
fault and phase-to-phase (
R1Zx
,
X1Zx
,
X0Zx
and
R0Zx
, x=2-5 or RV).
Theory of operation
SEMOD154224-46 v6
The mho algorithm is based on the phase comparison of an operating phasor and a polarizing
phasor. When the operating phasor leads the reference polarizing phasor by 90 degrees or more,
the function operates and gives a trip output.
Phase-to-phase fault
SEMOD154224-240 v2
Mho
GUID-D162893C-918A-4DDA-AAC2-0D0A814D85C1 v1
The plain Mho circle has the characteristic as in figure
155. The condition for deriving the angle β is
according to equation
84.
Section 7 1MRK 502 066-UUS B
Impedance protection
310
Technical manual
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