Page 22 - Power Quality in Electrical Systems

6 Chapter One

Spectral
amplitude

f
0 75 kHz 150 kHz 225 kHz 300 kHz
Figure 1.4 Typical interharmonic spectra produced by a high-
frequency switching power supply with switching frequency
75 kHz. We see interharmonics at multiples of 75 kHz.

Other sources of interharmonics are cycloconverters, arc furnaces,
and other loads that do not operate synchronously with the power-line
frequency [1.41].
High-frequency components can interfere with other electronic sys-
tems nearby and also contribute to radiated electromagnetic interfer-
ence (EMI). Medical electronics is particularly susceptible to the effects
of EMI due to the low-level signals involved. Telephone transmission can
be disrupted by EMI-induced noise.
This recent emphasis on the purity of delivered power has resulted
in a new field of study—that of “power quality.”

The Definition of Power Quality
Power quality, loosely defined, is the study of powering and ground-
ing electronic systems so as to maintain the integrity of the power
8
supplied to the system. IEEE Standard 1159 defines power quality as
[1.23]:
The concept of powering and grounding sensitive equipment in a manner
that is suitable for the operation of that equipment.
Power quality is defined in the IEEE 100 Authoritative Dictionary of
IEEE Standard Terms as ([1.42], p. 855):
The concept of powering and grounding electronic equipment in a manner
that is suitable to the operation of that equipment and compatible with the
premise wiring system and other connected equipment.

8
IEEE Std. 1159-1995, section 3.1.47, p. 5.