Page 99 - Power Quality in Electrical Systems
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82 Chapter Six
nonlinear load. The capacitors of the filter also provide reactive power
at the fundamental frequency (60 Hz) for power factor correction. The
filter is usually made up of one or more sections, as shown in Figure
6.10 [6.5]. The single-tuned RLC filter for each harmonic frequency
is the most common.
The impedance Z of the single-tuned section shown in Figure 6.11a
is given by:
2 X )
Z 5 R 1 j(X L c
where:
X 5 vL
L
1
X 5
C
vC
20
10
Amps 0
−10
−20
0.0 0.2 0.4 0.6 0.8 1.0
Time (sec)
100%
90%
80% I THD = 8.60%
70% = 148.2 A
I RMS
60% I Fund = 115.4 A
50%
40%
30%
20%
10%
0%
1 3 5 7 9 11 13 15 17 19 21 23 25
Harmonic number
(a)
Figure 6.9 Input waveforms to a 100-hp ASD, from [6.4]. (a)
Without an input line reactor, the line current THD 80.6 per-
cent; (b) with a 3-percent line reactor, the line current THD
37.7 percent.
[© 1999, IEEE, reprinted with permission]
