Ieee std 1159-1995, ieee recommended Practice for Monitoring Electric Power Quality

8.4.6 Harmonic analysis
8.4.6.1 Scope
Harmonics produce steady-state distortion of a voltage or current signal when compared to a pure sine wave.
Although harmonics have always been present in the power system, the advent of computers and power
conversion devices has forever altered the Òsine wave mentalityÓ of electrical theory, design, and practical
application.
8.4.6.2 Analysis tips
Three techniques for analyzing harmonics will be examined in subclauses 8.4.6.2.1 through 8.4.6.2.3. The
Þrst involves several simple ways of determining whether harmonics are present in the power system. The
second provides help in determining what particular type of load may be contributing to harmonic distortion.
The last looks at how harmonic data can be used to produce an impedance spectrum of the power system.
8.4.6.2.1 Harmonic presence
Before expensive harmonic-measuring equipment is rented or purchased, several easy tasks can be done to
determine if harmonics are present. The measurement requires both true rms and conventional measuring
devices. If the answer to any of the following questions is yes, then harmonics are present (see Þgure 10).
Ñ
Is the crest factor (ratio of peak to rms) of the voltage or current different than 1.4?
Ñ
Is the form factor (ratio of rms to average) of the voltage or current different than 1.1?
Ñ
Do the readings from a true rms meter differ from those of an averaging type meter? 
Ñ
Is the neutral current in a panel greater than what is expected due to simple imbalance?
Figure 20ÑModel for generation of load induced transients

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IEEE
MONITORING ELECTRIC POWER QUALITY
Std 1159-1995
57
8.4.6.2.2 Generic harmonic spectrums
If harmonics are present in the power system, then further investigation typically requires the use of a har-
monics analyzer. Such a device can provide speciÞc information about harmonic levels. Some of these pro-
vide only the total harmonic distortion (THD), while others provide THD and a full harmonic spectrum.
Harmonic spectrums can be very useful in gaining insight into the general type of load(s) which may be con-
tributing to the overall distortion.
Three generic harmonic spectrum signatures are described in the following. Keep in mind that these are gen-
eral descriptions only.
a)
If there are signiÞcant even order harmonics, then the signal is not symmetrical with respect to the
zero axis.
b)
Single-phase power conversion devices will typically produce high third harmonic current distortion
with an exponential decay of each successive odd harmonic.
c)
Three-phase rectiÞers will produce higher current harmonics in accordance with
where
h is the harmonic order
k is constant 1, 2, etc.
q is the number of pulses of rectiÞer
The highest harmonic will occur at k = 1 and +1, the next at k = 1 and Ð1. Each successive set of harmonics
will be smaller. Thus, a six-pulse rectiÞer will have a high Þfth and seventh (1
´ 6 ±1), then smaller eleventh
and thirteenth (2
´ 6 ±1), and so forth. See [B13].