J-4
Example Calculations for 87L Settings
Date Code 20010625
SEL-311L Instruction Manual
Source S
Z
1S
Source R
Relay 1
m • Z
1L
(1 - m) • Z
1L
Relay 2
Z
1R
I
1S
I
1R
+
Z
2S
Relay 1
m • Z
2L
(1 - m) • Z
2L
Relay 2
Z
2R
I
2S
I
2R
M311L144
—
I
1T
Z
0S
Relay 1
m • Z
0L
(1 - m) • Z
0L
Relay 2
Z
0R
I
0S
I
0R
0
I
1T
3 • R
F
I
TOTAL
+ = Positive-Sequence Network
– = Negative-Sequence Network
0 = Zero-Sequence Network
Figure J.3: Sequence Connection Diagram for an A-Phase Ground Fault
Summary
System non-homogeneity and non-zero load angle can add to create a 20° angular difference
between I
AR
and I
AL
. Continuing with our worst-case scenario for setting 87LANG, we must
consider the additional sources of angle errors from CT saturation (40°) and communication
channel asymmetry (22.5°). The sum of these worst-case errors, and assuming that they all
occur simultaneously, is 82.5°. Given this analysis, set 87LANG = 195°.
Summary of Contents for SEL-311L
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