Sel 751A - Figure 9.4 Derivation of Event Report Current Values and RMS Current Values from Sampled Current Waveform

9.13
Date Code 20100129 Instruction Manual SEL-751A Relay
Analyzing Events
Event Reporting
In Figure 9.4, note that any two rows of current data from the event report in
Figure 9.3, 1/4 cycle apart, can be used to calculate rms current values.
Figure 9.4 Derivation of Event Report Current Values and RMS Current
Values From Sampled Current Waveform
In Figure 9.5, note that two rows of current data from the event report in
Figure 9.3, 1/4 cycle apart, can be used to calculate phasor rms current values.
In Figure 9.5, at the present sample, the phasor rms current value is:
Equation 9.1
The present sample (IA = 940.7 A) is a real rms current value that relates to
the phasor rms current value:
Equation 9.2
(752.0)
2
+ (–941.0)
2
= 1204
(–750.3)
2
+ (940.7)
2
= 1204
(–941.0)
2
+ (–750.3)
2
= 1204
Event Report Column
752.0
–941.0
–750.3
940.7
IA
1
2
2
2
Multiply by
1
Multiply by
940.7
–941.0
–750.3
752.0
–1061.1
–1330.8
1063.5
1330.4
t
IA (peak)
1/4 cyc.
IA
peak
= 1703A
peak
1703 A
peak
= 1204 A
RMS
•
•
•
752.0
—941.0
—750.3
940.7
•
•
•
IA 1204 A 38.6°–∠=
1204 A cos 38.6°–()• 940.7 A=