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6

Power electronic

equipment

6.1 Introduction

Reactive power compensation in electric power systems is very important as
explained in earlier chapters. In this chapter, we examine closer how compensators
are realized in practice using the semiconductors and associated technology pre-
sented in Chapter 5.
In the first part of the chapter, the static compensators are presented. This kind of
equipment belongs to the class of active compensators. Furthermore, static means
that, unlike the synchronous condenser, they have no moving parts. They are used
for surge-impedance compensation and for compensation by sectioning in long-
distance, high-voltage transmission systems. In addition they have a variety of
load-compensating applications. Their practical applications are listed in greater
detail in Table 6.1. The main headings in Table 6.1 will be recognized as the
fundamental requirements for operating an AC power system, as discussed in pre-
vious chapters. Other applications not listed in Table 6.1, but which may nevertheless

Table 6.1 Practical applications of static compensators in electric power systems
Maintain voltage at or near a constant level
under slowly varying conditions due to load changes
to correct voltage changes caused by unexpected events (e.g. load rejections, generator and line outages)
to reduce voltage flicker caused by rapidly fluctuating loads (e.g. arc furnaces).
Improve power system stability
by supporting the voltage at key points (e.g. the mid-point of a long line)
by helping to improve swing damping.
Improve power factor
Correct phase unbalance