Schweitzer Engineering Laboratories SEL-421-4 - Page 340

6.4
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
230 kV Overhead Distribution Line Example
Breaker Monitor
Circuit Breaker Configuration
Set the relay to indicate that Circuit Breaker 1 is a three-pole trip circuit breaker.
BK1TYP := 3. Breaker 1 Trip Type (Single-Pole = 1, Three-Pole = 3)
Circuit Breaker 1 Inputs
The SEL-421 uses a normally open auxiliary contact from the circuit breaker to
determine whether the circuit breaker is open or closed.
52AA1 := IN101. A-Phase N/O Contact Input -BK1 (SELOGIC Equation)
Group Settings
Line Configuration
The SEL-421 has four transformer turns ratio settings that convert the secondary
potentials and currents that the relay measures to the corresponding primary val-
ues. These settings are the potential transformer and current transformer ratios
PTRY, PTRZ, CTRW, and CTRX.
Use the Y potential input for line relaying and the Z potential input for synchro-
nism check. Use the W current input for line relaying. The settings VNOMY and
VNOMZ specify the nominal secondary line-to-line voltage of the potential
transformers (see Figure 6.2).
CTRW := 100. Current Transformer Ratio—Input W (1–50000)
PTRY := 2000. Potential Transformer Ratio—Input Y (1–10000)
VNOMY := 115. PT Nominal Voltage (L-L)—Input Y (60–300 V secondary)
PTRZ := 2000. Potential Transformer Ratio—Input Z (1–10000)
VNOMZ := 115. PT Nominal Voltage (L-L)—Input Z (60–300 V secondary)
Enter the secondary value of the positive-sequence impedance of the protected
line. See Ta b l e 6 .2 for the secondary line impedances.
Z1MAG := 1.95. Positive-Sequence Line Impedance Magnitude
(0.05–255  secondary)
Z1ANG := 84.00. Positive-Sequence Line Impedance Angle (5.00–90 degrees)
Enter the secondary value of the zero-sequence impedance of the protected line.
Z0MAG := 6.20. Zero-Sequence Line Impedance Magnitude
(0.05–255  secondary)
Z0ANG := 81.50. 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. For this example, set the length in
miles.
LL := 50. Line Length (0.10–999)