Electrical Power Systems Quality
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Both electric utilities and end users of electric power are becoming
increasingly concerned about the quality of electric power. The term
power quality has become one of the most prolific buzzwords in the
power industry since the late 1980s. It is an umbrella concept for a multitude
of individual types of power system disturbances. The issues
that fall under this umbrella are not necessarily new. What is new is
that engineers are now attempting to deal with these issues using a
system approach rather than handling them as individual problems.
There are four major reasons for the increased concern:
1. Newer-generation load equipment, with microprocessor-based controls
and power electronic devices, is more sensitive to power quality
variations than was equipment used in the past.
2. The increasing emphasis on overall power system efficiency has
resulted in continued growth in the application of devices such as
high-efficiency, adjustable-speed motor drives and shunt capacitors
for power factor correction to reduce losses. This is resulting in
increasing harmonic levels on power systems and has many people
concerned about the future impact on system capabilities.
What Is Power Quality?
There can be completely different definitions for power quality, depending
on one’s frame of reference. For example, a utility may define power
quality as reliability and show statistics demonstrating that its system
is 99.98 percent reliable. Criteria established by regulatory agencies
are usually in this vein. A manufacturer of load equipment may define
power quality as those characteristics of the power supply that enable
the equipment to work properly. These characteristics can be very different
for different criteria.
Why Are We Concerned about Power
The ultimate reason that we are interested in power quality is economic
value. There are economic impacts on utilities, their customers,
and suppliers of load equipment.
The quality of power can have a direct economic impact on many
industrial consumers. There has recently been a great emphasis on
revitalizing industry with more automation and more modern equipment.
This usually means electronically controlled, energy-efficient
equipment that is often much more sensitive to deviations in the supply
voltage than were its electromechanical predecessors. Thus, like
the blinking clock in residences.
The Power Quality Evaluation
Power quality problems encompass a wide range of different phenomena,
as described in Chap. 2. Each of these phenomena may have a
variety of different causes and different solutions that can be used to
improve the power quality and equipment performance. However, it is
useful to look at the general steps that are associated with investigating
many of these problems, especially if the steps can involve interaction
between the utility supply system and the customer facility. Figure
1.2 gives some general steps that are often required in a power quality
investigation, along with the major considerations that must be
addressed at each step.
The general procedure must also consider whether the evaluation
involves an existing power quality problem or one that could result from
a new design or from proposed changes to the system.
Who Should Use This Book
Power quality issues frequently cross the energy meter boundary
between the utility and the end user. Therefore, this book addresses
issues of interest to both utility engineers and industrial engineers and
technicians. Every attempt has been made to provide a balanced
approach to the presentation of the problems and solutions.
The book should also be of interest to designers of manufacturing
equipment, computers, appliances, and other load equipment. It will
help designers learn about the environment in which their equipment
must operate and the peculiar difficulties their customers might have
when trying to operate their equipment. Hopefully, this book will serve
as common ground on which these three entities—utility, customer,
and equipment supplier—can meet to resolve problems.
This book is intended to serve both as a reference book and a textbook
for utility distribution engineers and key technical personnel with industrial
end users. Parts of the book are tutorial in nature for the newcomer
to power quality and power systems, while other parts are very technical,
intended strictly as reference for the experienced practitioner.