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7.4
Full-scheme distance measuring, Mho characteristic
ZMHPDIS
SEMOD154227-1 v4
7.4.1
Identification
SEMOD154447-2 v2
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE
C37.2 device
number
Full-scheme distance protection,
mho characteristic
ZMHPDIS
S00346 V1 EN-US
21
7.4.2
Application
SEMOD154444-1 v1
7.4.2.1
Functionality
SEMOD154453-4 v6
Transmission and sub-transmission networks are being extended and often become more and
more complex, consisting of a high number of multi-circuit and/or multi terminal lines of very
different lengths. These changes in the network will normally impose more stringent demands
on the fault clearing equipment in order to maintain an unchanged or increased security level
of the power system.
Full-scheme distance measuring, mho characteristic function (ZMHPDIS) in the IED is designed
to meet basic requirements for application on transmission and sub-transmission lines (solid
earthed systems) although it also can be used on distribution levels.
7.4.2.2
System earthing
SEMOD154453-11 v3
The type of system earthing plays an important role when designing the protection system. In
the following some hints with respect to distance protection are highlighted.
Solid earthed networks
SEMOD154453-14 v5
In solid earthed systems the transformer neutrals are connected solidly to earth without any
impedance between the transformer neutral and earth.
IEC05000215 V2 EN-US
Figure 136: Solidly earthed network
The earth-fault current is as high as or even higher than the short-circuit current. The series
impedances determine the magnitude of the earth-fault current. The shunt admittance has
very limited influence on the earth-fault current. The shunt admittance may, however, have
some marginal influence on the earth-fault current in networks with long transmission lines.
1MRK 505 343-UEN B
Section 7
Impedance protection
219
Application manual
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