Sel 751A - Figure 9.5 Derivation of Phasor RMS Current Values from Event Report Current Values

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.