ELECTRONIC PRINCIPLES - OD1647 - LESSON 1/TASK 1
equal to I2R. However, this loss can be greatly reduced if the
power is transmitted over the lines at a very high voltage level
and a low current level. This is not a practical solution to
the power loss in the dc system since the load would then have
to be operated at dangerously high voltage. Because. of the
disadvantages related to transmitting and using direct current,
practically all modern commercial electric power companies
generate and distribute alternating current (ac).
Unlike direct voltages, alternating voltages can be stepped up
or down in amplitude by a device called a TRANSFORMER. Use of
the transformer permits efficient transmission of electrical
power over longdistance lines. At the electrical power
station, the transformer output power is at high voltage and low
current levels. At the consumer end of the transmission lines,
the voltage is stepped down by a transformer to the value
required by the load. Due to its inherent advantages and
versatility, alternating current has replaced direct current in
all but a few commercial power distribution systems.
c. Voltage Waveforms. We now know that there are two types of
current and voltage, that is, direct current and voltage and
alternating current and voltage. If a graph is constructed
showing the amplitude of a dc voltage across the terminals of a
battery with respect to time, it will appear as in figure 52,
view A, on the following page. The dc voltage is shown to have
a constant amplitude. Some voltages go through periodic changes
in amplitude like those shown in figure 52, view B. The pattern
which results when these changes in amplitude with respect to
time are plotted on graph paper is known as a WAVEFORM. Figure
52, view B, shows some of the common electrical waveforms. Of
those illustrated, the sine wave will be dealt with most often.
d. Electromagnetism. The sine wave illustrated in figure 52,
view B, is a plot of a current which changes amplitude and
direction. Although there are several ways of producing this
current, the method based on the principles of electromagnetic
induct ion is by far the easiest and most common method in use.
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