Schweitzer Engineering Laboratories SEL-421-4 - Figure 6.15 Load-Encroachment Function

6.67
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Applications Examples
345 kV Tapped Overhead Transmission Line Example
SOTF Duration
Setting SOTFD determines the longest period the SOTF logic can assert after the
circuit breaker closes.
SOTFD := 10.000. Switch-Onto-Fault Enable Duration (0.500–16000 cycles)
Close Signal Monitor
Assign the Relay Word bit CLSMON to a control input, so the relay can detect
execution of the close command.
CLSMON := IN102. Close Signal Monitor (SELOGIC Equation)
Load Encroachment
The relay uses a load-encroachment feature that prevents operation of the phase-
distance elements during heavy load. This unique feature permits the load to
enter a predefined area of the phase-distance characteristics without causing
unwanted tripping. Figure 6.15 illustrates the load-encroachment function super-
imposed on the mho phase-distance protection characteristics.
Define the load-encroachment characteristic with load impedance settings in the
forward (ZLF) and reverse (ZLR) directions. Define the two load sectors, export
and import, with angle settings PLAF, NLAF, PLAR, and NLAR in the forward
and reverse directions.
Figure 6.15 Load-Encroachment Function
IMPORT EXPORT
Z2P
Z3P
R
1
X
1
Z1P
PLAF
NLAF
PLAR
NLAR
ZLR ZLF