Schweitzer Engineering Laboratories SEL-421-4 - Page 1084

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
—378
—107
378
107
—267
—267
—76
266
76
•
•
•
IA
Y = previous 1/4 cycle
X = present sample
Y = —267
θ
X = —76
—76
266
76
1/4 cycle
Raw Waveform
multiply by
2
2
Event Report Column Data
(—76)
2
+ (—267)
2
= 276.6
θ = arctan( )
Y
X
= arctan( )
—267
—76
= —105.9 degrees