R.1.58
SEL-421 Relay Reference Manual Date Code 20111215
Protection Functions
Mho Phase Distance Elements
Mho Phase Distance Elements
The SEL-421 has five independent zones of mho phase distance protection.
The mho phase distance protection operates for phase-to-phase, phase-to-
phase-to-ground, and three-phase faults. Set the reach for each zone
independently. Zone 1 and Zone 2 distance elements are forward only, while
you can set Zone 3 through Zone 5 distance elements either forward or
reverse. The mho phase distance elements use positive-sequence voltage
polarization for security, and also generate a dynamic expanding mho
characteristic that provides additional fault resistance coverage.
NOTE: The SEL-421-1 and the
SEL-421-2 provide fast and secure
tripping but do not have high-speed
distance elements. Typical detection
time for the SEL-421-1 and for the
SEL-421-2 is 1.5 cycles.
The SEL-421 has three independent zones of high-speed mho phase distance
protection. The high-speed mho phase distance protection operates for phase-
to-phase, phase-to-phase-to-ground, and three-phase faults. The first three
zones of mho phase ground distance protection (Zone 1, Zone 2, and Zone 3)
are for high-speed operation; typical detection time is less than one cycle.
Table 1.46 Mho Phase Distance Element Settings
Name Description Range
Default
(5 A)
E21P Mho Phase Distance Zones N, 1–5 3
Z1P Zone 1 Reach () OFF (0.25–320)/I
nom
6.24
Z2P Zone 2 Reach () OFF, (0.25–320)/I
nom
9.36
Z3P Zone 3 Reach () OFF, (0.25–320)/I
nom
1.87
Z4P Zone 4 Reach () OFF, (0.25–320)/I
nom
OFF
Z5P Zone 5 Reach () OFF, (0.25–320)/I
nom
OFF
Table 1.47 Mho Phase Distance Elements Relay Word Bits (Sheet 1 of 2)
Name Description
MAB1 Zone 1 A-phase-to-B-phase mho distance elements
MBC1 Zone 1 B-phase-to-C-phase mho distance elements
MCA1 Zone 1 C-phase-to-A-phase mho distance element
MAB2 Zone 2 A-phase-to-B-phase mho distance element
MBC2 Zone 2 B-phase-to-C-phase mho distance element
MCA2 Zone 2 C-phase-to-A-phase mho distance element
MAB3 Zone 3 A-phase-to-B-phase mho distance element
MBC3 Zone 3 B-phase-to-C-phase mho distance element
MCA3 Zone 3 C-phase-to-A-phase mho distance element
MAB4 Zone 4 A-phase-to-B-phase mho distance element
MBC4 Zone 4 B-phase-to-C-phase mho distance element
MCA4 Zone 4 C-phase-to-A-phase mho distance element
MAB5 Zone 5 A-phase-to-B-phase mho distance element
MBC5 Zone 5 B-phase-to-C-phase mho distance element
MCA5 Zone 5 C-phase-to-A-phase mho distance element
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