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5.86
SEL-421 Relay
Instruction Manual
Date Code 20171021
Protection Functions
Quadrilateral Phase-Distance Elements
Because Zone 1 and Zone 2 operate in the forward direction, the left blinder in
the reverse direction is the lowest setting among Zones
m
(
m
= 3–5). Zones set to
OFF (XP
m
= OFF), forward looking zones (DIR
m
= F) and zones not included in
the E21XP setting are excluded from the calculations to determine the minimum
RP value in the reverse direction.
TANGP, the tilt angle setting, tilts the reactance values, but does not affect the
resistance values.
shows the quadrilateral phase characteristic with
TANGP = 0 degrees.
shows the quadrilateral phase-distance element characteristic with
TANGP = –10 degrees. Notice that the reactance elements are tilted by
10 degrees, but the resistance blinders are unaffected by this setting. Also notice
that the pivot point of the tilt is the line impedance and not the reactance axis.
Furthermore, there are no individual TANGP settings for each zone; when you
enter a value other than zero for TANGP, all enabled zones are tilted by the same
value.
Figure 5.66
Quadrilateral Phase-Distance Element Characteristic (TANGP = 0)
Zone 3
Zone 2
Zone 1
Z1ANG
RP1
XP1
XP2
XP3
jX
—RP
RP2
RP3
R
Summary of Contents for SEL-421-4
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