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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Distribution of electricity. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric power supply Outdoor networks. Electrical energy is supplied to an apartment, individual house, villa or country house at a nominal voltage of 220 V through outgoing lines of the distribution network, which originate at a transformer substation (TS). Electricity is supplied to the transformer substation in most cases by three-phase current through three-wire high-voltage lines at a voltage of 6 to 35 kV, and is diverted through three-phase four-wire: three phase wires, the fourth - zero or neutral. In cities, lines are laid with cables in the ground, in rural areas - overhead lines (VL). In this case, bare wires are mounted on porcelain or glass insulators, mounted on wooden, reinforced concrete or metal supports. If street lighting is provided along the overhead line, another ("lantern") wire is laid. It is mounted on the supports of the outgoing overhead line, resulting in a five-wire line. Street lighting is connected to the "lantern" and neutral wires. To control street lighting, a switching device (switch or magnetic starter) is installed and a "lantern" wire and one of the phase wires are connected to its contacts. In four-wire electrical networks, the neutral wire must be grounded. Grounding is being built at the transformer substation. In addition, every 100-200 m along the route of the outgoing overhead lines and on the end supports, re-grounding the neutral wire is arranged.
1 - transformer substation; 2 - fuses and automatic switches in phase wires A, B and C (it is forbidden to install protective and switching devices in the neutral wire); 3 - building with two-wire single-phase input: phase A or B (C) and zero; 4 - building with four-wire three-phase input; 5 - a semi-detached house with a three-wire branch (single-phase input to each apartment); 6 - ground loop of the substation; 7 - street lighting lamp; 8 - repeated earthing along the route; 9 - cable line; 10 - input device (power box) From a four- or five-wire overhead line, which usually runs along a rural street, taps are made to consumers, distributing the load on each phase more or less evenly. With two-wire (single-phase) branches, this is achieved by alternating them from each phase of the overhead line. For example, a tap is made from the first phase to the first consumer, from the second to the second, from the third to the third, to the fourth - again from the first, etc. The other wire of each two-wire tap is connected to the neutral wire of the overhead line. There are also three- and four-wire branches: sometimes three-wire ones are made to two-apartment houses for power supply of two consumers from different phases with a common neutral wire, four-wire ones - to apartment buildings, in order to evenly distribute the loads of each apartment over the phases. The more evenly the electrical loads are distributed over the phases, the less the power loss. Four-wire branches are also performed for consumers with three-phase power receivers. Electric receivers of one- and three-phase current. Previously, electricity was used in everyday life only for lighting, and an electric lamp is a single-phase power receiver, therefore single-phase current has become widespread among individual consumers. Such a power supply system did not cause difficulties with the introduction of electric heaters, radio-electronic equipment and household appliances, since it does not affect the consumer properties of these devices, whether they are intended for single- or three-phase current. Other position with electric motors. The simplest in design, simple in operation and the most widespread in terms of application under production conditions, three-phase asynchronous motors cannot operate efficiently with a single-phase current. Therefore, in household electric vacuum cleaners, washing machines, compression refrigerators, various kitchen machines, as well as in power tools, single-phase electric motors are used. It must be admitted that, firstly, they are more complicated than three-phase ones, and secondly, they are less economical. As the power of single-phase electric motors increases, their disadvantages compared to three-phase motors become more and more noticeable. So, with a power of 1,3 kW, single-phase electric motors are so bulky that their use in everyday life becomes difficult. This power began to be considered the limit for household electrical appliances (with the exception of floor electric stoves). In addition, apartment wiring in old buildings is not suitable for turning on electrical appliances with a power of more than 1,3 kW. In order to intensify work in personal subsidiary plots, collective gardens and orchards, there was a need for more powerful electrified machines and tools with three-phase electric motors. Distribution systems. Between any pair of phase wires there is a linear, or interphase voltage, and between any of the phase and zero - phase. Under normal operating conditions, the line voltage is 1,73 times the phase voltage. So, if the linear voltage is 380 V, then the phase voltage is 220 V. It is customary to characterize three-phase electrical networks by the value of the linear voltage, but for networks that directly serve the population, the value of the phase voltage is given after the linear voltage, i.e., a three-phase four-wire system with a line voltage of 380 V denote 380/220 V. A three-phase 380/220 V system with a grounded neutral has become predominant, but other systems can also be found: a three-phase 220 V with an ungrounded (insulated) neutral without a neutral wire or a single-phase three-wire 2x220 V with a grounded middle wire. In a three-phase system without a neutral wire, single-phase receivers are connected to any pair of phase wires, evenly distributing loads across the phases; three-phase - to three phase wires. An electric shock in the event of an insulation fault with an isolated neutral is less likely than with a grounded one, but it is more difficult to find the fault. A single-phase 2x220 V system is used in small settlements (about a dozen houses). Two-wire branches are carried out to consumers - from the grounded and from one of the ungrounded wires. At the same time, an equal number of consumers are trying to be connected to each of the ungrounded wires. With such a system, three-phase receivers are not used. It happens that when using a 380/220 V system, difficulties arise with the supply of three-phase current to consumers, for example, if a group of consumers located away from a four-wire overhead line has a common branch from the neutral wire and not from all phase, but only from one or two. Author: Bannikov E.A.
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Comments on the article: Karpenko Alexander Filippovich Hello friends in misfortune! I have long been interested in the question of a grounded neutral wire. Does it really need to be grounded? This article writes that with an ungrounded neutral wire, it is difficult to troubleshoot the network. But is this difficulty commensurate with human casualties with a grounded neutral wire. How many thousands and thousands, I'm not afraid of this word, people died who stood on the ground and accidentally touched the phase wire. I myself was "beaten" by a current of 220 volts more than once. But it's good that it "beat" and not killed. And how many people were killed ... And only from the fact that the grounded neutral wire. I think it's time to think about it. Nicholas I am writing a thesis on the topic of power supply of a settlement with the development of a special issue "load distribution over the phases of overhead lines" I am interested in the question of how it all happens, why it is necessary and what is needed for this ![[cry]](https://diagram.com.ua/comments/smilies/cry.gif){kind=small}
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