Power supply


Power supply

Power supply serves for electricity supply of all industries of economy: industries, agriculture, transport, municipal economy, etc. The power sources raising and step-down substations the electric, feeding distribution network circuits, different auxiliary devices and constructions enter the utility power system. The main part of the developed electric power is consumed by the industry (for example, in the USSR — about 70% in 1977). The structure of power supply is defined by historically developed features of production and electric power distribution in the certain countries. The principles of creation of utility power systems in industrialized countries are the general.

Схема подачи электроснабжения потребителям

Scheme of giving of power supply to consumers.

Some specifics and local differences in schemes of power supply depend on the sizes of the territory of the country, its climatic conditions, level of economic development, industrial output and density of placement of the electrified objects and their power consumption.

Power sources. Main power supplies the electric power — power plants and power lines of regional power generating systems (See. Power generating system stability). At the industrial enterprises and in the cities for the combined supply with energy and heat use combined heat and power plants which power is defined by the need for heat for technology needs and heating. For the large power-intensive enterprises, for example steel works with big heatconsumption and the considerable exit of secondary energy resources, powerful combined heat and power plants at which install the generators developing current up to 20 kV are constructed. Such power plants which are usually located outside the plant at distance up to 1 — 2 km have regional value and, except the enterprise, supply with electrical energy and heat nearby industrial and residential areas. For unloading of power sources in rush hours so-called "consumers regulators" who without essential damage to technology process allow breaks or restrictions in electric power consumption serve. The majority of the electric furnaces possessing the considerable thermal lag, some electrolysis installations which allow to level schedules of loadings in power generating systems is among such electroreceivers, for example.

Схема глубоких вводов 110 и 220 кВ: а - радиальная; б - магистральная; ПГВ - подстанции глубокого ввода; УРП - узловая распределительная подстанция.

Figure 1. Scheme of deep inputs of 110 and 220 kV: and - radial; - main; PGV - substations of deep input; URP - nodal distribution substation.

Tension in utility power systems is the best values checked in practice. In each case voltage selection depends on delivered power and (from power source distance to the consumer) are characteristic of other countries. In scales of some countries there is tension of intermediate values which was entered at the early stage of construction of network circuits and continue to be used though in some cases already and are not optimum.

The power supply by the electric power of large industrial and transport enterprises and municipal economy is carried out at the voltage of 110 and 220 kV (in the USA often of 132 kV), and for especially large and power-intensive — 330 and 500 kV. Energy distribution at the first steps at the same time is carried out at the voltage of 110 or 220 kV. Voltage of 110 kV is applied more often since in this case it is easier to place overhead power transmission lines in the built-up territories of the enterprises and the cities. Energy distribution between consumers at the voltage of 220 kV is reasonable when this tension is as well feeding. Under certain conditions the mains voltage of 60 — 69 kV has advantages (it is applied in a number of countries of Western Europe and in the USA). Voltage of 35 kV is used in the feeding and distribution networks of the industrial enterprises of mean power, in the small and average cities and in rural network circuits and also for the power supply on large enterprises of powerful electroreceivers: electric furnaces, vypryamitelny installations, etc. Voltage of 20 kV is used rather seldom for development of the networks having this tension; it can be reasonable in areas with the small density of electric loadings and also in big cities and on large enterprises in the presence

Combined heat and power plant with generating voltage of 20 kV. Tension of 10 and 6 kV applies at electric power distribution (at different steps of power supply) at the industrial enterprises, in the cities, etc. This tension is suitable also for the power supply of the objects of small power nearby remote from the power source. Use of voltage of 10 kV as the basic is in most cases reasonable. At the same time the power supply of electric motors is made from step-down substations 10/6 kV according to the scheme the transformer — the engine or from windings of 6 kV of the transformer 110/220 of kV with the split secondary winding.

Schemes of utility power systems build proceeding from the principle of the greatest possible approach of the source of the electric power of the highest tension to electric units of consumers with the minimum quantity of steps of intermediate switching and transformation. Apply so-called deep inputs (35 — 220 kV) to these purposes cable and overhead power transmission lines. Step-down substations are placed in the centers of the arrangement of the main consumers of electricity, i.e. in the centers of electric loadings. As a result of such placement loss of the electric power decreases, the consumption of materials is reduced, the number of intermediate network links decreases, the operating mode of electroreceivers improves. Elements of the utility power system bear the permanent load, are calculated on mutual reservation taking into account admissible overloads and reasonable restriction of electric power consumption and in postemergency operation when recovery work on the damaged element or the site of network is performed. Separate work of elements with use of means of automatic equipment and deep sectioning of all links is in most cases provided. Parallel work is applied only at necessary justifications.

Deep inputs carry out the trunk and radial lines (fig. 1) depending on environmental conditions, building of the territory, etc. factors. The scheme of input of cable radial lines directly in the transformer of substation is the elementary the most compact and reliable. When using deep inputs application of the compact, completely closed KRUE cells (complete will distribute, devices with gas-insulated filling) on voltage of 110 kV is possible.

 Схемы сетей 6 и 10 кВ: а — двухступенчатая радиальная с промежуточными распределительными пунктами (РП); б — магистральная с токопроводами; в — двухлучевая с автоматическим включением резерва (АВР) на напряжение 0,4 кВ; ГПП — главная понизительная подстанция; ТП — трансформаторная подстанция.

Figure 2. Schemes of networks 6 and 10 of kV: and — two-level radial with the intermediate distribution points (DP); — main with current-conducting wires; in — dual-beam with the automatic inclusion of the reserve (AIR) on voltage of 0,4 kV; GPP — the main step-down substation; TP — transformer substation.

Will distribute schemes, networks 6 — 20 kV carry out main, radial or mixed (fig. 2) with modifications on reliability degree. The first steps of power supply of large enterprises usually carry out according to the main schemes with powerful current-conducting wires of 6 — 10 kV from which through distribution points shop transformer points eat. In city networks at voltage of 6 and 10 kV apply the loopback, dual-beam and multibeam schemes which are kinds of main.

On large nodal substations of 110 — 220 kV (at the big plants, in the cities with the developed network circuit, the large number of accessions, etc.) circuitries usually have the double system of tires. At voltage of 6 and 10 kV in large distributing devices in case of need divisions of the power supply or allocation of consumers (for example, on large converter substations) the double system of tires allows to transfer some units to the lowered tension, keeping normal stress for other consumers. In consumer electric units most often use schemes of substations with one system of sectioned tires using (if necessary) automatic equipment on section switches or inputs. At frequent operational switchings and audits (surveys and checks) of switches schemes with the bypass (additional) system of tires which allows to make audit or repair of any working system of tires and any switch without interruption of the power supply are reasonable. These schemes apply, for example, on large electrooven substations of the industrial enterprises. The simplest schemes of substations without tires of primary voltage on substations of deep inputs of 210 and 220 kV and on transformer substations of 10 and 6 kV fed according to block schemes the line — the transformer are distributed (see fig. 1 and 2). On transformer substations on the party of 10 and 6 kV put loading switches, and at the radial power supply apply deaf connection of transformers.
On large objects construction of network circuits with powerful current-conducting wires 10 and 6 of kV (instead of the large number of cables), cable platforms and galleries (instead of expensive and bulky tunnels), laying of cables 110 and 220 of kV is rational (instead of air-lines).

Reliability of power supply depends on requirements of uninterrupted operation of operation of electroreceivers. Necessary degree of reliability is defined by that possible damage which can be caused to production at the termination of their power supply. There are 3 categories of reliability of electroreceivers. Refer to the 1st category those which power supply is provided not less than 2 independent automatically reserved the source. Such electroreceivers are necessary on objects with increased requirements to uninterrupted operation of work (for example, process chemical production). The best in this case schemes of power supply with territorially separated independent sources. The admissible break in power supply for some productions should not exceed 0,15 — 0,25 sec. therefore the important condition is necessary high-speed performance of recovery of the power supply. For especially responsible electroreceivers provide the additional third source in the scheme of power supply. The electroreceivers allowing the power supply break for time necessary for inclusion of the manual reserve belong to the 2nd category. For receivers of the 3rd category the power supply break for a while up to 1 days, necessary on replacement or repair of the damaged system element is allowed.

Electric power quality. Electroreceivers which operation is followed by shock loads often enter utility power systems and reflects adversely at operation of other ("quiet") electroreceivers, the general regime of work of system, on electric power quality (see the Electric power quality). Valve inverters, arc electric furnaces, electrowelding machines, electric locomotives which work is followed by sharply variable pushes of loading, fluctuations of tension, decrease in electrical power factor, formation of the upper harmonics, emergence not of symmetry of tension belong to such electroreceivers. Quality characteristics of the electric power improve at increase in power of the short circuit in the point of network to which priklyuchena electroreceivers with adverse characteristics. To create such conditions, reduce the condensance of the feeding lines, without turning on in them reactors electric (See the Reactor electric) or reducing their reactivity, excluding from schemes current-conducting wires, etc. At the same time the disconnected power of switches has to be respectively increased.

Support of lines of the elektroperedachvoprosa of improvement of electric power quality are solved in a complex at design of utility power systems and the electric drive. Good results are yielded by division of the power supply of electroreceivers with shock and so-called quiet loads by accession them to different transformers and different branches of the split transformers or shoulders of dual reactors. Improvement of electric power quality is promoted by implementation in schemes of power supply of electric drives with the lowered consumption of reactive power, application of multiphase rectification circuits, etc. At insufficiency of these actions use special devices: the synchronous compensators with high-speed excitation, big frequency rate of the overload on reactive power (by 3 — 4 times) working in the so-called mode of tracking the reactive power of electroreceivers; the synchronous electric motors with quiet loading attached to the tires, general with valve inverters, and having the necessary located power and high-speed excitation with the high level of the forsirovka; static sources of reactive power with high high-speed performance, without inertance and smooth change of reactive power; the longitudinal capacitive compensation giving the chance of instant inertialess and continuous automatic control of tension; power tuned electrical wave filters for clearing of the upper harmonics.

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