9.17
Date Code 20170601
Instruction Manual
SEL-387-0, -5, -6 Relay
Event Reports and SER
Standard 15-, 30-, or 60-Cycle Event Reports
Figure 9.6
Derivation of Event Report Current Values and RMS Current
Values From Sampled Current Waveform
, note that any two rows of current data from the event report that
are one-quarter cycle apart, can be used to calculate rms current values. One-
quarter cycle represents 90 electrical degrees, so the two samples are
effectively perpendicular to each other and can be treated as rectangular
components of the phasor quantity. By using the normal method of taking the
square root of the sum of the squares of the samples, the magnitude of the
phasor can be extracted. Since the actual sample values have been divided by
the square root of two (multiplied by 1/sqrt(2) in the drawing) before being
entered into the report column, no further adjustment is needed after doing the
magnitude calculation. In the example in
, successive pairs of
samples result in magnitude calculations very close to the true value of
2748 A, rms. The true rms value is shown as IA
peak
times 1/sqrt(2) = 3887 •
0.707 = 2748 A.
event report column
1379
–2376
–1375
2380
2380
–1375
–2376
1379
IA
2
1
2
multiply by
2
1
multiply by
2380
–2376
–1375
1379
–1945
–3360
1950
3366
t
IA
1/4 cyc.
IApeak = 3887 Apeak
3887Apeak = 2748 Arms
(1379)2 + (–2376)2 = 2747
(–2376)2 + (–1375)2 = 2745
(–1375)2 + (2380)2 = 2749
Содержание SEL-387-0
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