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16 Electrical power systems ± an overview

These factors coupled with the ongoing deregulation and open access electricity
markets, where large consumers may shop around for competitively priced, high-
quality electricity, have propelled the distribution industry into unprecedented
change. On the technical front, one major development is the incorporation of power
electronics controllers in the distribution system to supply electricity with high
quality to selected customers. The generic, systematic solution being considered by the
utility to counter the problem of interruptions and low power quality at the end-user
level is known as Custom Power. This is the low voltage counterpart of the more
widely known FACTS technology.
Although FACTS and custom power initiatives share the same technological base,
they have different technical and economic objectives (Hingorani and Gyugyi, 2000).
Flexible alternating current transmission systems controllers are aimed at the trans-
mission level whereas Custom Power controllers are aimed at the distribution level, in
particular, at the point of connection of the electricity distribution company with
clients with sensitive loads and independent generators. Custom Power focuses
primarily on the reliability and quality of power flows. However, voltage regulation,
voltage balancing and harmonic cancellation may also benefit from this technology.
The STATCOM, the DVR and the solid state switch (SSS) are the best known
Custom Power equipment. The STATCOM and the DVR both use VSCs, but the
former is a shunt connected device which may include the functions of voltage
control, active filtering and reactive power control. The latter is a series connected
device which precisely compensates for waveform distortion and disturbances in the
neighbourhood of one or more sensitive loads. Figure 1.10 shows the schematic
representation of a three-phase STATCOM. Figure 1.14 shows that of a DVR and
Figure 1.15 shows one phase of a three-phase thyristor-based SSS.
The STATCOM used in Custom Power applications uses PWM switching control
as opposed to the fundamental frequency switching strategy preferred in FACTS
applications. PWM switching is practical in Custom Power because this is a relatively
low power application.
On the sustainable development front, environmentally aware consumers and
government organizations are providing electricity distribution companies with a
good business opportunity to supply electricity from renewable sources at a pre-
mium. The problem yet to be resolved in an interconnected system with a generation
mix is how to comply with the end-user's desire for electricity from a renewable
source. Clearly, a market for renewable generation has yet to be realized.

1.3.4 Utilization

The customers of electricity vendors may be classified as industrial, commercial and
domestic (Weedy, 1987). In industrialized societies, the first group may account for
as much as two fifths of total demand. Traditionally, induction motors have formed
the dominant component in the vast array of electric equipment found in industry,
both in terms of energy consumption and operational complexity. However, compu-
ter-assisted controllers and power electronics-based equipment, essential features in
modern manufacturing processes, present the current challenge in terms of ensuring
their trouble-free operation. This equipment requires to be supplied with high quality
electricity.