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J-6
Example Calculations for 87L Settings
Date Code 20010625
SEL-311L Instruction Manual
If the current transformer ratio for this 15 kV application is 60:1 (300/5), the phase charging
current is 1 A secondary, and the negative-sequence charging current (3I
2
) is 0.03 A secondary.
Again, make setting 87L2P = 0.5 A for excellent security and sensitivity.
Ground Fault Resistance Coverage With 87L2P = 0.5 A
In both examples, setting 87L2P = 0.5 A secondary allows ground fault resistance coverage up
to:
R
F
=
Ω
=
8
.
132
A
5
.
0
V
4
.
66
secondary
2
2
Assumes load current less than 1/3 of nominal secondary current. See Figure 3.8 for
ground fault resistance coverage with more load current.
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