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9.20
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
Reporting
Event Reports, Event Summaries, and Event Histories
NOTE:
The arctan function of many
calculators and computing programs
does not return the correct angle for
the second and third quadrants (when
X is negative). When in doubt, graph
the X and Y quantities to confirm that
the angle that your calculator reports
is correct.
Figure 9.8
Event Report Current Column Data and RMS Current Angle
0
t
—3
78
—1
07
37
8
10
7
—2
67
—267
—76
266
76
•
•
•
IA
Y = previous 1/4 cycle
X = present sample
Y = —
26
7
θ
X = —76
—7
6
26
6
76
1/4 cycle
Raw Waveform
multiply by
2
2
Ev
ent R
eport C
olumn Dat
a
(—
76)
2
+ (—
26
7)
2
= 2
76.6
θ
= arctan
(
)
Y
X
= arctan
(
)
—267
—76
= —105.9 degrees
Summary of Contents for SEL-421-4
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