Page 17 - Power Quality in Electrical Systems

Chapter
1

Introduction

In this introductory chapter, we shall attempt to define the
term “power quality,” and then discuss several power-quality
“events.” Power-quality “events” happen during fault
conditions, lightning strikes, and other occurrences that
adversely affect the line-voltage and/or current waveforms. We
shall define these events and their causes, and the possible
ramifications of poor power quality.

Background
In recent years, there has been an increased emphasis on, and concern
for, the quality of power delivered to factories, commercial establish-
ments, and residences [1.1–1.15]. This is due in part to the preponder-
ance of harmonic-creating systems in use. Adjustable-speed drives,
switching power supplies, arc furnaces, electronic fluorescent lamp bal-
lasts, and other harmonic-generating equipment all contribute to the
harmonic burden the system must accommodate [1.15–1.17]. In addi-
tion, utility switching and fault clearing produce disturbances that
affect the quality of delivered power. In addressing this problem, the
Institute of Electrical and Electronics Engineers (IEEE) has done sig-
nificant work on the definition, detection, and mitigation of power-
quality events [1.18–1.27].
Much of the equipment in use today is susceptible to damage or serv-
ice interruption during poor power-quality events [1.28]. Everyone with
a computer has experienced a computer shutdown and reboot, with a loss
of work resulting. Often, this is caused by poor power quality on the 120-V
line. As we’ll see later, poor power quality also affects the efficiency and oper-
ation of electric devices and other equipment in factories and offices
[1.29–1.30].

1
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