Date Code 20010625
Loss-of-Potential, CCVT Transient Detection,
4-7
Load-Encroachment, and Directional Element Logic
SEL-311L Instruction Manual
Again, for the maximum forward load:
[(230)
2
• (400)]/[(800) • (2000)] = 13.2
8
secondary
To provide a margin for setting ZLF, multiply by a factor of 0.9:
ZLF = 13.2
8
secondary • 0.9 = 11.90
8
secondary
For the maximum reverse load:
[(230)
2
• (400)]/[(500) • (2000)] = 21.1
8
secondary
Again, to provide a margin for setting ZLR:
ZLR = 21.1
8
secondary • 0.9 = 19.00
8
secondary
Convert Power Factors to Equivalent Load Angles
The power factor (forward load) can vary from 0.90 lag to 0.95 lead.
Setting PLAF = cos
-1
(0.90) = 26
o
Setting NLAF = cos
-1
(0.95) = -18
o
The power factor (reverse load) can vary from 0.80 lag to 0.95 lead.
Setting PLAR = 180
o
- cos
-1
(0.80) = 180
o
- 37
o
= 143
o
Setting NLAR = 180
o
+ cos
-1
(0.95) = 180
o
+ 18
o
= 198
o
Apply Load-Encroachment Logic to a Phase Time-Overcurrent
Again, from Figure 4.3:
ZLOAD = ZLOUT + ZLIN
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