Date Code 20001006 Loss-of-Potential, Load Encroachment, and Directional Element Logic 4-3
SEL-351 Instruction Manual
LOAD-ENCROACHMENT LOGIC
The load-encroachment logic (see Figure 4.2) and settings are enabled/disabled with setting
ELOAD (= Y or N).
The load-encroachment feature allows phase overcurrent elements to be set independent of load
levels. This is especially helpful in bus overcurrent applications. A bus relay sees the cumulative
currents of all the feeders but still has to provide overcurrent backup protection for all these
feeders. If the phase elements in the bus relay are set to provide adequate backup, they often are
set close to maximum bus load current levels. This runs the risk of tripping on bus load current.
The load-encroachment feature prevents this from happening as shown in the example that follows
in this subsection.
Figure 4.2: Load-Encroachment Logic
Courtesy of NationalSwitchgear.com
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