Tài liệu Power quality

Power quality - C. SANKARAN

POWER QUALITY - C. SANKARAN (202 pages)

Preface
The name of this book is
Power Quality,
but the title could very well be
The Power
Quality Do-It-Yourself Book
. When I set out to write this book, I wanted it to be
user friendly, easy to understand, and easy to apply in solving electrical power system
problems that engineers and technicians confront on a daily basis. As an electrical
engineer dealing with power system quality concerns, many of the books I consulted
lacked direct and precise information and required a very thorough search to find
what I needed. Very often, I would spend several hours pondering a case just so the
theory I read and the practical findings would come together and make sense. This
book is the product of my thought processes over many years. I have tried to combine
the theory behind power quality with actual power quality cases which I have been
involved with in order to create a book that I believe will be very useful and demystify
the term
power quality
.
What is power quality? Power quality, as defined in this book, is “a set of electrical
boundaries that allows equipment to function in its intended manner without significant
loss of performance or life expectancy.” Conditions that provide satisfactory
performance at the expense of life expectancy or vice versa are not acceptable.
Why should power quality be a concern to facility designers, operators, and
occupants? When the quality of electrical power supplied to equipment is deficient,
performance degradation results. This is true no matter if the equipment is a computer
in a business environment, an ultrasonic imaging machine in a hospital, or a process
controller in a manufacturing plant. Also, good power quality for one piece of
equipment may be unacceptable for another piece of equipment sitting right next to
it and operating from the same power lines, and two identical pieces of equipment
can react differently to the same power quality due to production or component
tolerances. Some machines even create their own power quality problems. Given
such hostile conditions, it is important for an engineer entrusted with the design or
operation of an office building, hospital, or a manufacturing plant to be knowledgeable
about the basics of power quality.
This book is based on 30 years of personal experience in designing, testing, and
troubleshooting electrical power systems and components, the last 9 of which have
been spent exclusively studying and solving power quality problems for a wide
spectrum of power users. This book is not an assemblage of unexplained equations
and statements. The majority of the information contained here is based on my
experiences in the power system and power quality fields. Mathematical expressions
are used where needed because these are essential to explaining power quality and
its effects. Throughout the book, several case examples are provided, the steps used
to solve power quality problems are described in depth, and photographs, illustrations,
and graphs are used to explain the various power quality issues. The examples show
that many power quality problems that have resulted in loss of productivity, loss of
equipment, injury to personnel, and in some cases, loss of life could easily have been
avoided. All that is needed to prevent such consequences is a clear understanding of
electrical power quality and its effects on power system performance.
I hope the reader will enjoy reading this book as much as I enjoyed writing it.
Also, I hope the reader will find the book useful, as it is based on the experiences
of an electrical engineer who has walked through the minefields of electrical power
system quality and for the most part survived.
C. Sankaran



Contents
Chapter 1
Introduction to Power Quality
1.1 Definition of Power Quality
1.2 Power Quality Progression
1.3 Power Quality Terminology
1.4 Power Quality Issues
1.5 Susceptibility Criteria
1.5.1 Cause and Effect
1.5.2 Treatment Criteria
1.5.3 Power Quality Weak Link
1.5.4 Interdependence
1.5.5 Stress–Strain Criteria
1.5.6 Power Quality vs. Equipment Immunity
1.6 Responsibilities of the Suppliers and Users of Electrical Power
1.7 Power Quality Standards
1.8 Conclusions
Chapter 2
Power Frequency Disturbance
2.1 Introduction
2.2 Common Power Frequency Disturbances
2.2.1 Voltage Sags
2.3 Cures for Low-Frequency Disturbances
2.3.1 Isolation Transformers
2.3.2 Voltage Regulators
2.3.3 Static Uninterruptible Power Source Systems
2.3.4 Rotary Uninterruptible Power Source Units
2.4 Voltage Tolerance Criteria
2.5 Conclusions
Chapter 3
Electrical Transients
3.1 Introduction
3.2 Transient System Model
3.3 Examples of Transient Models and Their Response
3.3.1 Application of DC Voltage to a Capacitor
3.3.2 Application of DC Voltage to an Inductor
3.4 Power System Transient Model
3.5 Types and Causes of Transients
3.5.1 Atmospheric Causes
3.5.2 Switching Loads On or Off
3.5.3 Interruption of Fault Circuits
3.5.4 Capacitor Bank Switching
3.6 Examples of Transient Waveforms
3.6.1 Motor Start Transient
3.6.2 Power Factor Correction Capacitor Switching Transient
3.6.3 Medium Voltage Capacitor Bank Switching Transient
3.6.4 Voltage Notch Due to Uninterruptible Power Source Unit
3.6.5 Neutral Voltage Swing
3.6.6 Sudden Application of Voltage
3.6.7 Self-Produced Transients
3.7 Conclusions
Chapter 4
Harmonics
4.1 Definition of Harmonics
4.2 Harmonic Number (
h
)
4.3 Odd and Even Order Harmonics
4.4 Harmonic Phase Rotation and Phase Angle Relationship
4.5 Causes of Voltage and Current Harmonics
4.6 Individual and Total Harmonic Distortion
4.7 Harmonic Signatures
4.7.1 Fluorescent Lighting
4.7.2 Adjustable Speed Drives
4.7.3 Personal Computer and Monitor
4.8 Effect of Harmonics on Power System Devices
4.8.1 Transformers
4.8.2 AC Motors
4.8.3 Capacitor Banks
4.8.4 Cables
4.8.5 Busways
4.8.6 Protective Devices
4.9 Guidelines for Harmonic Voltage and Current Limitation
4.10 Harmonic Current Mitigation
4.10.1 Equipment Design
4.10.2 Harmonic Current Cancellation
4.10.3 Harmonic Filters
4.11 Conclusions
Chapter 5
Grounding and Bonding
5.1 Introduction
5.2 Shock and Fire Hazards
5.3 National Electrical Code Grounding Requirements
5.4 Essentials of a Grounded System
5.5 Ground Electrodes
5.6 Earth Resistance Tests
5.7 Earth–Ground Grid Systems
5.7.1 Ground Rods
5.7.2 Plates
5.7.3 Ground Ring
5.8 Power Ground System
5.9 Signal Reference Ground
5.10 Signal Reference Ground Methods
5.11 Single-Point and Multipoint Grounding
5.12 Ground Loops
5.13 Electrochemical Reactions Due to Ground Grids
5.14 Examples of Grounding Anomalies or Problems
5.14.1 Loss of Ground Causes Fatality
5.14.2 Stray Ground Loop Currents Cause Computer Damage
5.14.3 Ground Noise Causes Adjustable Speed Drives to Shut Down
5.15 Conclusions
Chapter 6
Power Factor
6.1 Introduction
6.2 Active and Reactive Power
6.3 Displacement and True Power Factor
6.4 Power Factor Improvement
6.5 Power Factor Correction
6.6 Power Factor Penalty
6.7 Other Advantages of Power Factor Correction
6.8 Voltage Rise Due to Capacitance
6.9 Application of Synchronous Condensers
6.10 Static VAR Compensators
6.11 Conclusions
Chapter 7
Electromagnetic Interference
7.1 Introduction
7.2 Frequency Classification
7.3 Electrical Fields
7.4 Magnetic Fields
7.5 Electromagnetic Interference Terminology
7.5.1 Decibel (dB)
7.5.2 Radiated Emission
7.5.3 Conducted Emission
7.5.4 Attenuation
7.5.5 Common Mode Rejection Ratio
7.5.6 Noise
7.5.7 Common Mode Noise
7.5.8 Transverse Mode Noise
7.5.9 Bandwidth
7.5.10 Filter
7.5.11 Shielding
7.6 Power Frequency Fields
7.7 High-Frequency Interference
7.8 Electromagnetic Interference Susceptibility
7.9 EMI Mitigation
7.9.1 Shielding for Radiated Emission
7.9.2 Filters for Conducted Emission
7.9.3 Device Location to Minimize Interference
7.10 Cable Shielding to Minimize Electromagnetic Interference
7.11 Health Concerns of Electromagnetic Interference
7.12 Conclusions
Chapter 8
Static Electricity
8.1 Introduction
8.2 Triboelectricity
8.3 Static Voltage Buildup Criteria
8.4 Static Model
8.5 Static Control
8.6 Static Control Floors
8.7 Humidity Control
8.8 Ion Compensation
8.9 Static-Preventative Casters
8.10 Static Floor Requirements
8.11 Measurement of Static Voltages
8.12 Discharge of Static Potentials
8.13 Conclusions
Chapter 9
Measuring and Solving Power Quality Problems
9.1 Introduction
9.2 Power Quality Measurement Devices
9.2.1 Harmonic Analyzers
9.2.2 Transient-Disturbance Analyzers
9.2.3 Oscilloscopes
9.2.4 Data Loggers and Chart Recorders
9.2.5 True RMS Meters
9.3 Power Quality Measurements
9.4 Number of Test Locations
9.5 Test Duration
9.6 Instrument Setup
9.7 Instrument Setup Guidelines
9.8 Conclusions