Page 126 - Power Quality in Electrical Systems

Chapter
8

Methods for Correction of

Power-Quality Problems

In this chapter we discuss methods of correction of power-
quality problems. Methods discussed include filters,
transformers, uninterruptible power supplies (UPSs) and
compensators.

Introduction

The first manifestation of a power-quality problem is a disturbance in the
voltage waveform of the power source from a sine wave, or in the ampli-
tude from an established reference level, or a complete interruption. The
disturbance can be caused by harmonics in the current or by events in
the supply system. The disturbance can last for a fraction of a cycle (mil-
liseconds) to longer durations (seconds to hours) in the voltage supplied
by the source. The disturbance usually becomes evident through mis-oper-
ation of the equipment supplied by the source, or because of a complete
shutdown. Certain power-quality problems, such as current or voltage
waveform distortion, will also appear as a result of a survey of a facility
using appropriate instruments, as described in Chapter 14.
The objective of a “method for correction” is to make the power source
meet a standard. For example, the standard can be for limits on rms volt-
age deviation in the form of an amplitude versus time chart, such as the
classical CBEMA curve (as described in Chapter 2). The standard can
be for voltage harmonic amplitudes in the form given in IEEE Std. 519.
The standard also can be expressed as the duration of outages in the util-
1
ity measure of SAIDI, or the number of nines in the reliability per unit

1
The SAIDI index is a standard measure of utility outage, and stands for “System
Average Interruption Duration Index.”
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