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2.10.2 Equations in distance protection function
(i) Element equations for Mho characteristic
The element of the Mho characteristic is achieved by comparing the angle between S1 and S2
phases, which are obtained in Equations (2.10-15) and (2.10-16) . If the angle between the S1
and the S2 is greater than 90°, a fault is being detected in the element in the Mho
characteristic; then a trip signal will be issued.
where
V = fault voltage
I = fault current
Zs = reach setting
Vp = polarizing voltage
Figure 2.10-4 Element in Mho characteristic
Figure 2.10-4 shows the Mho characteristic obtained by comparing phases, provided the
fault voltage (V) and the polarizing voltage (Vp) are in phase. In Figure 2.10-4 the Mho
characteristic is obtained by dividing the voltage (V) by the current (I).
The Mho characterize is provided to detect for both the distance relays in phase-to-phase
(ZS) and in ground-fault (ZG); a self-polarization in accompany with cross-polarization (i.e., a
dual polarization) is employed for the both characteristic. The polarizing voltage (Vp) is
expressed using Equations (2.10-17) and (2.10-18).
To the ZS element (for a fault in phase-bc):
To the ZG element (for an earth fault in phase-a):
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