Linear voltage in electrical networks

In each field of technology, one can always find a kind of echoes of ancient times, namely, names that reflect a kind of history of development of this direction. And very few people know that this or that technical concept has a long way of becoming addictive, and at the very beginning of its birth it marked the next, often very significant, step of technical progress. For example, among the electrical terms, it is very often possible to hear the expressions "three-phase voltage", "line voltage", "constant" or "alternating voltage" and many other names with the word "voltage".

Initially, as a physical value, the voltage is defined as the electric field potential difference, capable of performing work to move electric charge from one point of the field to another. The charge energy is consumed by the field energy, so its value, more precisely, the potential difference, decreases to zero. In a real closed circuit, work on moving electric charges is treated as an electric current - the result of moving electrons from one point of the chain to another. That it does not change, it is necessary to maintain the potential difference unchanged. As is known, the power source is responsible for maintaining the current in the circuit. It determines whether the current in the circuit is constant, i.e. Not changing its magnitude and direction, or variables that vary according to some law. The term "line voltage" is meaningful only for AC networks .

The greatest distribution in electrical engineering was obtained by alternating voltage networks of sinusoidal form. The maximum value of the voltage when it oscillates is called the amplitude Ua. For this voltage, additional units of measure are used - frequency F and phase ψ. The frequency is determined by the number of oscillations per unit time, and the phase is the time shift of identical oscillation points. It so happened historically that the term "phase" was also used to refer to the AC transmission line , if it is part of a multi-phase system, usually three. Three-phase networks were another achievement of electrical engineering and have so many advantages that it's simply impossible to pass by. And the most important of them is the possibility to obtain a rotating magnetic field without any effort, the basic principle of operation of any electric motor. The three-phase circuit distinguishes between phase and linear voltage, and its feature is that each phase has a shift relative to the remaining two +/- 120 degrees. The three-phase voltage generator has output windings in which the phase shift is structurally set. Each of the windings has an end and a beginning: H1-K1, H2-K2, H3-K3. In a three-phase system, two variants of phase connection are possible - "star" and "triangle".

When connecting the "star" all the ends are connected to one point - "terminal 0", and the beginning serves as the output ends for the generator and input terminals for the device powered by it. In such a system, the line voltage is a value measured between any pair of output ends H1, H2, H3, and it is designated Ulin. There is one more characteristic of the three-phase network - phase voltage. It is designated Uf and is measured between the points "lead 0" and any of the output ends K1, K2 and K3. Omitting the details, it should be noted that, based on the vector diagram for a three-phase network, the relationship between these voltages Ulin = Ѵ3 * Uf. When connecting the "triangle" the ends of the windings are connected along the ring: K1-H1-K2-H2-K3-H3-K1. Each end-start connection is an output, and the line voltage does not differ from the phase voltage; Ulin = Uf. It is interesting to compare the constant voltage Udir and the amplitude of the alternating voltage Ua, for example, based on the same energy released in the load. For this case Udir = Ѵ2 * Ua.

That's how for decades, accumulated knowledge about the nature and nature of electricity, and quietly the notion of "tension" has grown into related terms that expand our ability to use natural phenomena for human needs.