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Basics of Electricity
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Figure 1.17. Alternating current cycle.
Normal alternating current goes through many cycles each second. See
Figure 1.18. The number of cycles per second is measured in Hertz (Hz).
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In Europe and many other parts of
the world, alternating current is generated at 50 Hz, or 50 cycles per second.
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In United States, alternating
current is typically generated at 60 Hz, or 60 cycles per second.
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Figure 1.18. Alternating current frequency.
Voltage in a AC circuit is also represented by a sine wave. In
Figure 1.19, the current and voltage sine waves are superimposed on the same time
axis. Note the two wave forms rise and fall simultaneously.
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Figure 1.19. Single phase alternating current.
Single-phase and Three-Phase Alternating Current
There are two types of alternating current: single-phase and three-phase. The symbol for
phase is the Greek letter "phi" (Ø).
Figure 1.19 shows single phase AC as a series of single AC cycles. There are one
current and one voltage wave form. Single-phase AC power is produced by a single- phase generator
or by using one phase of the three-phase supply. Single-phase power is used for domestic premises
and small commercial installations.
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