Schweitzer Engineering Laboratories SEL-787 - Figure 9.4 Derivation of Analog Event Report Current Values and RMS Current Values from

9.12
SEL-787 Relay Instruction Manual Date Code 20081022
Analyzing Events
Event Reporting
Figure 9.4 Derivation of Analog 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 analog event report,
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=