What is alternating current?

About the varieties of electric current, everyone is told about physics lessons at school. For some, this knowledge remains only theoretical, expanding the understanding of the world order, while others choose a profession directly related to energy. Regardless of this, every person knows that there is a constant and alternating current. In electrical engineering, the second version is widely used, as it is easier to convert, and electric motors based on it are simpler and more reliable.

An alternating current is a motion along a conductor of charged particles, which changes at a certain time (periods) in direction and magnitude. The famous sine wave just illustrates his behavior. To understand where the alternating current comes from, let's consider the operation principle of the simplest generating device. It is based on the phenomenon of electromagnetic induction, consisting in the appearance of a current in a closed conducting circuit, which crosses the magnetic lines of force.

On the axis, between the two poles of the magnet (north and south), a frame of conductive material (copper wire) is placed. Its ends are connected by means of sliding contacts of the brush mechanism to the circuit with a load or a voltage measuring device. The frame can rotate about the axis on which it is placed. Between the poles of the magnet there are invisible magnetic lines of field strength. When the frame is rotated, its two sides intersect these lines, resulting in an alternating current. The reason for its occurrence is caused by "knocking out" the magnetic field of electrons from the orbits far from the nucleus. Although the directions of EMF (electromotive force) in the two intersecting sections of the frame are always opposite, if you look at the chain as a whole, it becomes clear that they are unidirectional. The EMF reaches its maximum at the moment of vertical intersection of the lines of force and passes through zero with the horizontal arrangement of the frame parts (remember the sinusoid, it also intersects the zero value periodically). It's that simple.

Of course, real alternating current generators look harder than the wire frame, but the principle of their operation is the same. An anchor with windings (in fact - many frames from the example) rotates an external force in the stator magnetic field: it can be the energy of the falling water; The movement of steam created by the heat of a nuclear reactor; Wind pressure, etc. As a result, voltage appears at the terminals of the windings. It remains to connect the load and the alternating current does not take long to wait. Generally, not one, but three phases are generated at once.

As already indicated, in addition to the variable, there is also a direct current. Its name speaks for itself: there are no changes in the direction of the movement. This current is always directed from plus to minus. Secondary sources of energy, for example batteries, accumulate just such a current through chemical reactions, hence the notation "+" and "-". In comparison with variables, it has a number of features. I want to say "advantages and disadvantages", but it is not so - it is "features". For example, a constant-current motor makes it possible to smoothly adjust the armature rotation speed, rather than stepwise and, moreover, without the need for complex frequency converters. Moreover, almost all electronic circuits are designed to work with this type of current, because it is easier to control. To obtain a constant current from a variable is very simple - it must be "straightened out" with special semiconductor elements (diodes and diode bridges). There is a cutoff of the sinusoidal peaks immediately in two half-cycles. The remaining pulsating nature of the resulting current can also be smoothened.