Any person who chooses to work with electrical engineering as their profession should be very well versed in what kind of power sources are, what are their features and differences. In fact, there is nothing complicated, which we will show in this article.
It is hard to imagine what the modern world would look like, if electric energy and related electrical appliances disappeared from it. Probably, mankind would still use steam engines and the muscular power of animals and their brothers. It is impossible to say unequivocally who exactly discovered electric energy for the first time: for example, spinners in ancient Syria used the ability of amber to magnetize (electrify), Aristotle tried to study the possibilities of electric stingray, but the danger of lightning has been known since the beginning of the world (it was not without reason that some nations deified it).
Electric current comes in two varieties - alternating and direct. This difference is due to the method of its preparation. Accordingly, alternating current power sources give a current of the first type, and direct current - of the second. By the way, here the division into "first - second" is arbitrary. In electrical engineering, both AC and DC power sources are used. Let's recall a little theory.
Any electric current is the movement of charged particles directed along the conductive material by the electromotive force of the EMF. External action gives some electrons located on the outer orbits of atoms an additional energy sufficient to overcome the attraction of the nucleus. As a result, free charge carriers appear - ions and electrons. According to the law of conservation of energy, a process of natural recombination of particles occurs at nearby atoms at the lattice sites. Without external influence, the structure of the material will be restored. However, if the EMF source is connected to the conductor, then the field generated by it directs the recombination in the desired direction - an electric current arises. The alternating current source is actually an emf generator, the directional vector of which periodically changes to the opposite. Hence the name "variable." AC power sources in most cases are represented by generating capacities - generators in modern power plants create exactly alternating current. They are more reliable in operation and easier to maintain than DC collector models. In the diagrams, AC power supplies are often indicated by a circle with a wave inside. This wave is a symbolic image of a sinusoid.
The alternating current source creates the movement of particles not only with a changing direction, but also with a "floating" effective value. The sine wave itself indicates that periodically the value passes through zero.
A completely different principle is based on direct current sources. They create in the conductor an unchanged in the direction of the electric field, forming a directed motion of particles having a charge. It is generally accepted that current flows from a positive to a negative contact (from positive to negative). In reality, the movement of electrons occurs in the opposite direction - from minus to plus. Since the charge of a single electron is negative, a pole with a minus sign indicates an excess of these particles (hence the total charge). Based on the fact that oppositely charged particles are mutually attracted, it is easy to guess that the electrons move from the “minus” to the “plus” along the conductor. An artificial change in the effective value is allowed - from this the current does not cease to be constant. There are a large number of different solutions that allow you to convert direct current to alternating current (sinusoidal generators) and vice versa (rectifiers, bridges).