4-4
Loss-of-Potential, CCVT Transient Detection,
Date Code 20011205
Load-Encroachment, and Directional Element Logic
SEL-311A Instruction Manual
Figure 4.3: Load-Encroachment Logic with Example Settings
A positive-sequence impedance calculation (Z
1
) is made in the load-encroachment logic in Figure
4.3. Load is largely a balanced condition, so apparent positive-sequence impedance is a good
load measure. The load-encroachment logic only operates if the positive-sequence current (I
1
) is
greater than the Positive-Sequence Threshold shown in Figure 4.3. For a balanced load
condition, I
1
= phase current magnitude.
Forward load (load flowing out) lies within the hatched region labeled ZLOUT. Relay Word bit
ZLOUT asserts to logical 1 when the load lies within this hatched region.
Summary of Contents for SEL-311A
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