P.3.178
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
Mho Ground-Distance Elements
Figure 3.120 Out-of-Step Blocking for Zone 1–Zone 5
Mho Ground-Distance Elements
The relay has five independent zones of mho ground distance protection. The
mho ground distance protection operates only for single phase-to-ground
faults. You can set the reach for each zone independently. Zone 1 and Zone 2
distance elements are forward only; you can set Zones 3–5 distance elements
either forward or reverse. The mho ground-distance elements use positive-
sequence voltage polarization for security and generate a dynamic expanding
mho characteristic.
NOTE: The -0 relay provides fast and
secure tripping but does not have
high-speed distance elements. Typical
detection time for the -0 relay is
1.5 cycles.
The -1 relay has three independent zones of high-speed mho ground distance
protection. The high-speed mho ground distance protection operates for single
phase-to-ground faults. The first three zones of mho ground distance
protection (Zones 1–3) are for high-speed operation; typical detection time is
less than one cycle.
The Zone 1 zero-sequence compensation factor (k01) is independent from the
forward and reverse compensation factors (k0 and k0R) the relay uses for the
other zones.
If you set k0M1 to AUTO, the relay automatically calculates the values k01,
k0, and k0R based on the following equation:
Equation 3.88
OSB1
OSB2
OSB3
OSB4
OSB5
OOSB1 = Y
OOSB5 = Y
OOSB4 = Y
OOSB3 = Y
OOSB2 = Y
EOOS = Y1
OSB
EOOS = Y
OOSDET
where:
Z
1L
= positive-sequence transmission line impedance
Z
0L
= zero-sequence transmission line impedance
k0
Z
0L
Z
1L
–
3Z
1L
•
------------------------=
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