Page 230 - Fluid Power Engineering

CHAPTER10

Basics of Electricity

and Generators

I shall make electricity so cheap that only the rich can afford
to burn candles
—Thomas Alva Edison

Introduction
In this chapter, the generator side of wind turbines is described. The
aerodynamics chapters alluded to the notion that the type of genera-
tor has a significant impact on the efficiency of the turbine rotor. These
aspects are covered in this chapter. The chapter starts with basic prin-
ciples of electromagnetism followed by basic principles of alternating
current and basic principles of electrical machines. This is followed by
descriptions of synchronous, permanent magnet, and asynchronous
generators. The chapter concludes with a comparison of most com-
monly used types of generators in wind turbines.

Basic Principles of Electromagnetism
A current carrying straight conductor creates a magnetic field (lines
of force) that is circular and in a plane that is perpendicular to the
conductor.
A current carrying circular conductor creates a magnetic field that
is perpendicular to the plane of the circular conductor.
A current carrying circular conductor that is cylindrically wound
in the form of a coil produces a magnetic field that is parallel to the
axis of the cylinder. When a core of ferromagnetic material is placed
inside the coil, then the magnetic field is magnified and this is called

197