7.3.6 Operation principle
SEMOD154230-1 v2
7.3.6.1 Full scheme measurement
SEMOD154224-4 v3
The execution of the different fault loops within the IED are of full scheme type, which means that
each fault loop for phase-to- ground faults and phase-to-phase faults are executed in parallel for
all zones.
The use of full scheme technique gives faster operation time compared to switched schemes
which mostly uses a phase selector element to select correct voltages and current depending on
fault type. So each distance protection zone performs like one independent distance protection
function with six measuring elements.
7.3.6.2 Impedance characteristic
SEMOD154224-11 v7
The Mho distance function ZMHPDIS is present with four instances so that four separate zones
could be designed. Each instance can be selected to be either forward or reverse with positive
sequence polarized mho characteristic; alternatively self polarized offset mho characteristics is
also available. One example of the operating characteristic is shown in Figure
98 A) where zone 5 is
selected offset mho.
The directional mho characteristic of Figure
98 has a dynamic expansion due to the source
impedance. Instead of crossing the origin as for the mho to the left of Figure 98, which is only
valid where the source impedance is zero, the crossing point is moved to the coordinates of the
negative source impedance giving an expansion of the circle of Figure
98 D) .
R
jx
Mho, zone4
Mho, zone3
Mho, zone2
Mho, zone1
X
Zs=0
R
Zs=Z1
Zs=2Z1
IEC11000223-2-en.vsd
C
D
IEC11000223 V2 EN-US
Figure 98: Mho characteristic and the source impedance influence on the mho characteristic
1MRK 502 066-UUS B Section 7
Impedance protection
219
Technical manual
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