9.14
SEL-751A Relay
Instruction Manual
Date Code 20100129
Analyzing Events
Event Reporting
Figure 9.5
Derivation of Phasor RMS Current Values From Event Report
Current Values
IA (RMS)
t
IA
Event Report Column
Magnitude =
X = 940.7
Y = —750.3
Angle
= Arctan
= Arctan
Y
X
—750.3
940.7
= –38.6˚
Real Axis
Axis
Imaginary
1/4 cyc.
(—750.3)
2
+ (940.7)
2
= 1204
Y = Previous
1/4 Cycle
•
•
•
752.0
—941.0
—750.3
940.7
•
•
•
X = Present Sample
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.
Summary of Contents for 751A
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