Power system fundamentals - Wind Power Integration: Connection and System Operational Aspects - page 21

Chapter 2
Power system fundamentals

2.1 Introduction

Most wind power capacity is connected to electricity supply networks, and this is likely
to continue for the foreseeable future. The advantages of connection to a grid include:

the ability to locate wind farms where the wind resource is plentiful, irre-
spective of demand;

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the ability of an interconnected grid to absorb variations in wind generation
unrelated to overall demand variation;

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provision of excitation, enabling simple induction machines to be used as
generators.

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These advantages are qualified by various limitations of the power supply
system, and Chapters 4 and 5 will consider how the resulting problems can be
overcome. However, the fact remains that grid connection has provided a major
impetus to the growth of wind energy. Hence it is important to understand the
fundamentals of electrical power engineering presented in this chapter.
The chapter will start with the basic principles of electrical engineering. The
discussion will lead naturally to the transformer, found in all wind farms as well as
throughout power supply systems. We then consider alternating current (AC) sys-
tems, with particular emphasis on active and reactive power and the use of phasors.
Power supply systems are then considered. The chapter will close with an intro-
duction to AC power transmission.

2.2 Basic principles

2.2.1 Electromagnetism
¨ ersted observed in 1820 that a magnetic compass needle is deflected by the flow
of electric current. He was able to show that the magnetic field may be represented
by concentric circles round the conductor axis. This is shown in Figure 2.1.
Note that current flowing away - represented by an ' ' produces a clockwise
field. Current flowing towards the observer - represented by a ' ' - produces an
anti-clockwise field. This relationship between field and current direction is known
as the right-hand screw rule: a right-handed screw will move away (the current)
when the screw is rotated clockwise (the field).