Schweitzer Engineering SEL-387-0 - Figure 9.7 Derivation of Phasor RMS Current Values from Event Report Current Values

9.18
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Event Reports and SER
Standard 15-, 30-, or 60-Cycle Event Reports
Figure 9.7 Derivation of Phasor RMS Current Values From Event Report
Current Values
In Figure 9.7, note that two rows of current data one-quarter cycle apart can be
used to calculate phasor rms current values. At the time of interest, the present
sample is used as the Real Axis, or “X” component, while the value from one-
quarter cycle before is used as the Imaginary Axis, or “Y” component.
Plotting the components as shown, and noting that the angle of the phasor is
Arctan(Y/X), the complete phasor quantity can be derived and compared with
other current phasors calculated from other current pairs selected from the
same two rows of the Event Report. In Figure 9.7 at the present sample the
phasor rms current value is:
Equation 9.1
IA
t
IA
1
3
7
9
–
2
3
7
6
–
1
3
7
5
2
380
event re
p
ort colum
n
X=
p
resent sam
p
l
e
Y=
p
reviou
s
1/4 c
y
cl
e
Magnitude =
X = 2
380
Y
=
–
13
7
5
An
g
le = Ar
ctan
= Ar
cta
n
Y
X
(
)
–
2
380
(
)
=
–
30.0
˚
R
ea
l Axi
s
A
xi
s
I
ma
g
inary
1/4 cyc.
(
–
1375
)
2
+
(
–
2380
)
2
= 274
9
IA 2749 A 30.0–=