Page 25 - Power Quality in Electrical Systems

Introduction 9

cycloconverters, arc furnaces, and other systems that draw current not
in synchronization with the line frequency [1.51–1.61]. Such fluctua-
tions can result in variations in the lighting intensity due to an effect
known as “flicker” which is visible to the end user.
■ A voltage “imbalance” is a variation in the amplitudes of three-phase
voltages, relative to one another.

The need for corrections
Why do we need to detect and/or correct power-quality events
[1.63–1.64]? The bottom line is that the end user wants to see the non-
interruption of good quality electrical service because the cost of down-
time is high. Shown in Table 1.1, we see a listing of possible mitigating
strategies for poor power quality, and the relative costs of each.

The Scope of This Text

We will address the significant aspects of power quality in the follow-
ing chapters:

Chapter 1, Introduction, provides a background for the subject, includ-
ing definitions, examples, and an outline for the book.
Chapter 2, Power Quality Standards, discusses various power-quality
standards, such as those from the IEEE and other bodies. Included
are standards discussing harmonic distortion (frequencies that are
multiples of the line frequency) as well as high-frequency interhar-
monics caused by switching power supplies, inverters, and other high-
frequency circuits.
Chapter 3, Voltage Distortion, discusses line-voltage distortion, and
its causes and effects.
Chapter 4, Harmonics, is an overall discussion of the manner in which
line-voltage and line-current distortion are described in quantitative
terms using the concept of harmonics and the Fourier series, and
spectra of periodic waveforms.
Chapter 5, Harmonic Current Sources, discusses sources of harmonic
currents. This equipment, such as electronic converters, creates fre-
quency components at multiples of the line frequency that, in turn,
cause voltage distortion.
Chapter 6, Power Harmonic Filters, discusses power harmonic fil-
ters, a class of equipment used to reduce the effect of harmonic cur-
rents and improve the quality of the power provided to loads. These
filters can be either passive or active.