Electrical Fundamentals - Concepts of Alternating Current
A. Bhatia, B.E.
The electricity you get from your electric outlet is alternating current (AC). There are many appliances such as computer and TVs that actually work on DC while other electrical appliances, such as refrigerators, air-conditioners, lighting etc… can be designed for both AC and DC.
Since some kinds of loads only require DC to power them and others can easily operate on either AC or DC, the question naturally arises, "Why not dispense entirely with AC and just use DC for everything?" This question is augmented by the fact that in some ways AC is harder to handle as well as to use. Nevertheless, there is a very practical reason, which overrides all other considerations for a widely distributed power grid. It all boils down to a question of cost.
This 3-hr course material provides insight to the basic concepts of alternating current and is based entirely on Naval Education and Training Materials (NAVEDTRA 14173), Electricity and Electronic Training Series; Module-2 "Concepts of Alternating Current" and covers Chapter 1.
The course includes
a multiple-choice quiz at the end, which is designed to enhance the understanding
of course materials.
At the conclusion of this course, the student will be able to:
This course is aimed at students, professional engineers, service technicians, energy auditors, operational & maintenance personnel, facility engineers and general audience.
AC stands for Alternating
Current. The current flows in one direction for a period of time and then switches
direction, going the opposite way. It switches direction over and over again
continuously. In the United States the AC current in power lines goes switches
direction, forward to backward, then backward to forward, 60 times each second.
This is a frequency of 60 cycles and is called 60Hertz AC electricity.
The usual waveform of an AC power circuit is a sine wave, which results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves. The alternating voltage and current have a number of properties associated with any such waveform. The most important of these properties are frequency and amplitude, since some types of electrically powered equipment must be designed to match the frequency and voltage of the power lines. Wavelength is not generally important in this context, but becomes much more important when we start dealing with signals at considerably higher frequencies.
In this course, you
are required to study Naval Education and Training Materials (NAVEDTRA 14173),
Electricity and Electronic Training Series; Module-2 "Concepts of Alternating
Current" Chapter 1:
Concepts of Alternating Current (Chapter 1, NAVEDTRA 14173)
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Alternating current, or sine wave, is produced by an alternating voltage source that reaches a maximum in one direction (+), decreases to zero, reverses itself, and continues in the opposite direction until a maximum is reached. The cycle repeats continuously. The sine wave is the most common type of waveform. It is so named because it changes in value at the ramp rate, as the trigonometric function known as the sine.
AC transmission uses voltages ranging from 200 to 600 thousand volts. To meet customer demands the power company installs a transformer at different points along the AC power transmission line to lower the output voltage. Various potentials are involved. For homes and commercial buildings, it is lowered to the 220/120 volt level and for industrial use it is 220 volts and above. The AC voltage is usually transmitted at higher voltages which mean lower current for the same power, and less resistive loss. This is the major benefit AC provides over DC for large distance transmissions.
This course familiarizes you with the definitions of the following referenced terms.
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.