TABLE OF CONTENTS Over the last 10 years both operators and customers have taken an increasing interest in the quality of the power, or more precisely the quality of the voltage, which is delivered by distribution networks. This interest has been stimulated by a number of factors, including [1]:
increasingly sensitive load equipment, which often includes computer-based controllers and power electronic converters which can be sensitive to variations in voltage magnitude, phase and frequency
the proliferation of power electronic switching devices on the network, including the power supplies of small items of equipment such as PCs and domestic equipment, and the rise in background harmonic voltage levels on the electricity supply network
increased sophistication of industrial and commercial customers ofthe network and concern over the effect, and commercial consequences, of perceived poor power quality on their equipment and hence production. This particularly concerns the effect of voltage dips or sags on continuous industrial processes.
Although the main issues of power quality are common to any distribution network, whether active or passive, the addition of embedded generation can have a significant effect and, as usual, increases the complexity of this aspect of distribution engineering. Some forms of embedded generation can introduce non-sinusoidal currents into the distribution network and so degrade power quality by causing harmonic voltage distortion while other types can cause unacceptable variations in RMS voltage magnitudes. Perhaps surprisingly, embedded generators may also improve network power quality by effectively increasing the short-circuit level of part of the distribution network.
Figure 5.1 shows...
