Download Wind Energy an Introduction - Mohamed a. El-Sharkawi (CRC, 2016) PDF

TitleWind Energy an Introduction - Mohamed a. El-Sharkawi (CRC, 2016)
File Size20.2 MB
Total Pages345
Table of Contents
                            Front Cover
Contents
Preface
Author
List of Variables
Chapter 1: History of the Wind Energy Development
Chapter 2: Aerodynamics of Wind Turbines
Chapter 3: Wind Statistics
Chapter 4: Overview of Wind Turbines
Chapter 5: Solid-State Converters
Chapter 6: Induction Generator
Chapter 7: Synchronous Generator
Chapter 8: Type 1 Wind Turbine System
Chapter 9: Type 2 Wind Turbine System
Chapter 10: Type 3 Wind Turbine System
Chapter 11: Type 4 Wind Turbine
Chapter 12: Grid Integration
Back Cover
                        
Document Text Contents
Page 1

K24400

Wind Energy: An Introduction covers wind energy system types, operation,

modeling, analysis, integration, and control. Beginning with a history of the

development of wind energy, this comprehensive book:

• Explains the aerodynamic theories that govern the operation of
wind turbines

• Presents wind energy statistics to address the stochastic nature
of wind speed

• Employs the statistical modeling of wind speed to evaluate sites for
wind energy generation

• Highlights the differences between the most common types of
wind turbines

• Analyzes the main power electronic circuits used in wind energy
• Details the induction, synchronous, and permanent magnet generators

from the basic principle of induced voltage to the steady-state
and dynamic models

• Explores the operation, stability, control, and protection of type
1, 2, 3, and 4 wind turbines

• Discusses the main integration challenges of wind energy systems
with electric utility systems

• Features numerous models, illustrations, real-world examples,
and exercise problems

• Includes a solutions manual and �gure slides with qualifying
course adoption

Wind Energy: An Introduction requires a basic knowledge of electric circuit
theory, making it an ideal text for students at the senior-undergraduate and
graduate levels. In addition, the book provides practicing engineers with a
handy professional reference.

Wind Energy AN INTRODUCTION

Engineering – Electrical

ISBN: 978-1-4822-6399-2

9 781482 263992

90000

Page 172

149

7
Synchronous Generator

The synchronous generator is the most popular machine used to generate electricity
in power plants. Worldwide, over 98% of all electric power is generated by the syn-
chronous generators. The machine has excitation circuit connected to the rotor. For
small-sized generators, the excitation is produced by ferrite permanent magnetic mate-
rial. This is the most economic design for fractional horsepower generators that do not
experience repeated surges in stator currents (repeated surges can demagnetize the
rotor). In better designs, the rotor is made of rare earth permanent magnetic material
such as the samarium–cobalt to produce stronger magnetic fields. One great advan-
tage of generators built with rare earth material is their high power/volume ratios
that make them small in size and weight. The strong rare earth permanent magnetic
material allows designers to build generators as large as 1.0 MW. Another advantage is
that the rare earth permanent magnet cannot be easily demagnetized, so it can be used
for applications where heavy currents and surges in currents are expected. Because of
these advantages, the rare earth permanent magnetic synchronous generator is used
in wind turbine.

For high power production, the field of the generator is electric to produce strong flux
intensity; this also allows the operator to control the terminal voltage and reactive power of
the generator. This type is used in conventional power plants and some large wind turbines.

7.1 Description of Synchronous Generator

The synchronous generator consists of a stator and a rotor, as shown in Figure 7.1a. The sta-
tor of the synchronous machine is similar to the stator of the induction machine; it consists
of three-phase windings mounted symmetrically inside the stator. The stator windings are
also known as “armature windings.” To produce electric field, the winding of the rotor is
excited by an external dc source through a slip-ring system. The rotor winding, which is
also known as “field winding” or “excitation winding,” produces a stationary flux (ϕf) with
respect to the rotor.

When a wind turbine spins the rotor of the synchronous generator, the magnetic
field cuts the stator windings, thus inducing sinusoidal voltages across the stator wind-
ings. Because the three stator windings are equally spaced from each other, the induced
voltages across the phase windings are shifted by 120° from each other, as shown in
Figure 7.1b.

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