Schweitzer Engineering Laboratories SEL-421-4 - Page 394

6.58
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
Set Z1MAG equal to Z1L1 plus Z1L2 so the fault locator provides correct results
for internal faults not located on the tap (i.e., source T is extremely weak and pro-
vides practically no infeed). See Table 6.15 for the secondary line impedances.
Z1MAG := 4.00. Positive-Sequence Line Impedance Magnitude
(0.05–255  secondary)
Z1ANG := 84.7. Positive-Sequence Line Impedance Angle (5.00–90 degrees)
Enter the secondary value of the zero-sequence impedance of the protected line
from Station S to Station R, ignoring the tap.
Z0MAG := 12.88. Zero-Sequence Line Impedance Magnitude
(0.05–255  secondary)
Z0ANG := 73.0. 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 := 100.00. 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 zones of phase mho (E21P), ground mho
(E21MG), and ground quadrilateral (E21XG) distance protection. You can inde-
pendently select the number of zones per type of distance protection. Select only
the number of zones needed. For this application example, use three zones of
mho phase and ground-distance protection.
E21P := 3. Mho Phase-Distance Zones (N, 1–5)
E21MG := 3. Mho Ground-Distance Zones (N, 1–5)
E21XG := N. Quadrilateral Ground-Distance Zones (N, 1–5)
Now enable the other logic you will need for this application example.
You do not need CVT transient detection if the SIR (Source Impedance Ratio) is
less than five. SIR is equal to the ratio of the local source impedance to the relay
reach. Calculate the ratio based on the Zone 1 reach because you do not want
Zone 1 distance protection to overreach during an external fault.
Equation 6.21
ECVT := N. CVT Transient Detection (Y, N)
NOTE: The SEL-421-4 does not
provide series-compensated line
protection logic.
The transmission line is not series compensated.
ESERCMP := N. Series-Compensated Line Logic (Y, N)
SIR
Z
1S
0.8 Z
1L1
Z
1L2
+•
------------------------------------------------=
0.67 
0.8 2  2 +•
---------------------------------------------=
0.209, SIR<5=