6.91
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
EHV Parallel 230 kV Underground Cables Example
Enter the secondary values of the positive-sequence impedance of the protected
cable. See Table 6.23 for the secondary cable impedances.
Z1MAG := 0.48. Positive-Sequence Line Impedance Magnitude (0.05–255
secondary)
Z1ANG := 42.5. Positive-Sequence Line Impedance Angle (5.00–90 degrees)
Enter the secondary values of the zero-sequence impedance of the protected
cable. The zero-sequence impedance should correspond to the parallel sheath and
ground fault return path (see Z0
L1(sheath and ground)
in Table 6 .2 3).
Equation 6.54
Z0MAG = 0.1 • |Z0
L1(sheath and ground)
| = 0.1 • |9.58 21.7°| = 0.96
Z0MAG := 0.96. Zero-Sequence Line Impedance Magnitude (0.05–255 sec-
ondary)
Z0ANG := 21.7. Zero-Sequence Line Impedance Angle (5.00–90 degrees)
Enable the fault locator.
EFLOC := Y. Fault Location (Y, N)
The LL setting is the line length. This value has no defined unit; you can set the
line length in miles, kilometers, ohms, etc. Set the length in miles.
LL := 25.00. Line Length (0.10–999)
The relay fault locator uses the values you enter for Z1MAG, Z1ANG, Z0MAG,
Z0ANG, and LL.
Relay Configuration
You can select from zero to five phase mho (E21P), ground mho (E21MG), and
ground quadrilateral (E21XG) distance zones. The number of zones per type of
distance protection is independently selectable. Select only the number of zones
you need. For this application example, use three zones of mho phase-distance
protection and three zones of quadrilateral ground-distance protection.
E21P := 3. Mho Phase-Distance Zones (N, 1–5)
E21MG := N. Mho Ground-Distance Zones (N, 1–5)
E21XG := 3. Quadrilateral Ground-Distance Zones (N, 1–5)
You do not need CVT (capacitive voltage transformer) transient detection
because PTs with wound windings are used for this particular application example.
ECVT := N. CVT Transient Detection (Y, N)
NOTE: The SEL-421-4 does not
provide series-compensated line
protection logic.
The underground cable is not series-compensated.
ESERCMP := N. Series-Compensated Line Logic (Y, N)
where:
k = the result of Equation 6.52
Z0MAG k Z0
L1 sheath and ground
• =
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