AC vs. DC
Electric current is the flow of electrons carrying electric charge. There are 2 types of electric current – direct (DC) and alternating (AC). In Direct Current the electron flow takes place only in one direction. A battery is a source of direct current. DC is widely used in many electronic circuits operating in low voltage levels.
In Alternating Current, both voltage and current alternate in direction back and forth following a sine wave pattern. The number of cycles per second, called the frequency, varies from 50 or 60 depending on the power system in a country. Alternating current is produced universally in power stations using AC generators. The AC theory is briefly described below.
A rotating coil in a magnetic field cuts the magnetic lines of force in two different directions during each half rotation in an AC generator. Thus the current produced travels alternately from left to right and then from right to left. When the coil is parallel to the magnetic lines of force, no current is generated. The alternating current so generated is collected by slip rings attached to the ends of the rotating coil and then transferred to an external circuit through metallic brushes.
Alternating current can be readily transmitted over long distances with minimum loss unlike DC. Any voltage drop along the way can be easily boosted using transformers. Also motors with high power can be designed using AC. Eddy current and radiation losses are the principal disadvantages of AC. 3 phase AC is generated in power stations, with each current out of phase by 120 deg to each other.
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