Schweitzer Engineering Laboratories SEL-421-4 - Figure 5.62 Zones 3, 4, and 5 Quadrilateral Ground-Distance Element Logic; Mho Phase-Distance Elements

5.80
SEL-421 Relay Instruction Manual Date Code 20171021
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 ele-
ments use positive-sequence voltage polarization for increased reliability and
also generate a dynamic expanding mho characteristic that provides additional
fault resistance coverage.
NOTE: The SEL-421-4 provides fast
and secure tripping but does not have
high-speed distance elements. Typical
detection time for the SEL-421-4 is
1.5 cycles.
The SEL-421 has five independent zones of quadrilateral phase-distance protec-
tion (see Quadrilateral Phase-Distance Elements on page 5.85). Although the
mho and quadrilateral phase elements are independent, you can enable both at the
same time. To this end, the outputs from the mho and quadrilateral phase ele-
ments are ORed to a single protection output (see Figure 5.61, Figure 5.64, and
Figure 5.65).
The SEL-421 has a settable Zone 1 overcurrent supervision setting for phase-
distance elements (Z50P1) and for ground-distance elements (Z50G1). These
advanced settings (EADVS = Y) apply to both mho and quadrilateral distance
Figure 5.62 Zones 3, 4, and 5 Quadrilateral Ground-Distance Element Logic
—
+
—
+
(Setting)
(Setting)
(Setting)
XGPOL := IG
32VE
XAGn
32QE
32GF
XGPOL := I2
DIRn := F
XGPOL := IG
32VE
(Setting)
(Setting)
32QE
32GR
XGPOL := I2
xAGR > —XGn
—RGn < rAGR < RGn
3PO
FSA
ILOP
VPOLV
xAGF < XGn
—RGn < rAGF < RGn
0.1 • I
NOM
IGL
IAL
SPO
(Relay Word Bit)
Zone 3, 4, and 5 Quadrilateral Ground
Distance Logic for A-phase
B- and C-Phase Logic is Similar
n = 3, 4, or 5
Relay
Word Bit
Relay
Word Bit
Relay
Word Bit
Relay
Word Bit
ARESE = N
ENX2AG