Schweitzer Engineering Laboratories SEL-751 - Figure 10.4 Derivation of Event Report Current Values and RMS Current Values from Sampled Current Waveform

10.17
Date Code 20170927 Instruction Manual SEL-751 Relay
Analyzing Events
Event Reporting
In Figure 10.4, note that you can use any two rows of current data from the
event report in Figure 10.3, 1/4 cycle apart, to calculate rms current values.
Figure 10.4 Derivation of Event Report Current Values and RMS Current
Values From Sampled Current Waveform
In Figure 10.5, note that you can use two rows of current data from the event
report in Figure 10.3, 1/4 cycle apart, to calculate phasor rms current values.
In Figure 10.5, at the present sample, the phasor rms current value is:
Equation 10.1
The present sample (IA = 940.7 A) is a real rms current value that relates to
the phasor rms current value:
Equation 10.2
(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=