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Chapter 7

Direct Current

Power Systems

Alternating Current (AC) is used in greater quantities than direct
current (DC); however, many important operations are dependent upon
DC power. Industries use DC power for many specialized processes.
Electroplating and DC variable-speed motor drives are only two exam-
ples that show the need for DC power to sustain industrial operations. We
use DC power to start our automobiles, and many types of portable equip-
ment in the home use DC power. Most of the electrical power produced
in the United States is three-phase AC, and this three-phase AC power may
be easily converted to DC for industrial or commercial use. Direct current
is also available in the form of primary and secondary chemical cells. These
cells are used extensively. In addition, DC generators are also used to sup-
ply power for specialized applications.

IMPORTANT TERMS

Chapter 7 deals with DC power systems. After studying this chapter,
you should have an understanding of the following terms:

Primary Cell
Secondary Cell
Electrolyte Electrode
Battery
Internal Resistance
Carbon-Zinc Cell
Mercury Cell
Alkaline Cell
Nuclear Cell
Lead-Acid Cell