Applications and Advantages of Alternating Quantities

Alternating current and three-phase current (a special form of alternating current) nowadays dominate most areas of electrical engineering, including energy technology, communications engineering and information technology. This is due, in particular, to the following advantages:

Large amounts of electrical energy are produced at power plants with the help of generators in which a turning rotor magnetically induces an alternating or three-phase voltage in a fixed stator. This type of configuration is not able to produce direct voltages without a means of conversion.
When electrical energy is transmitted over long distances, line losses occur. The higher the transmission voltage though, the lower the losses. With the help of transformers, that will be treated later in this course, alternating voltages can be easily stepped-up (e.g. to 380 kV) and then transmitted via high-tension lines; direct voltage cannot be transmitted economically in a similar manner.
Electric drives (motors) operate on a principle that is the converse of the generator principle, i.e. they convert electrical energy into rotational energy. Such motors can run on direct, alternating or three-phase current. Compared to DC motors, three-phase ones require much less maintenance and are better able to generate higher powers.
In communications engineering, high-frequency carrier signals may be used for analog radio transmission, for instance. By means of modulation, these signals are able to convey information such as music and speech. By using different carrier frequencies in a process termed multiplexing, it is possible to transmit several signals simultaneously on a common channel.



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