Course Design - Power Supply to Metallurgical Plant

Introduction

The design of any link of the power supply system of an industrial enterprise (site, department, workshop or plant as a whole) should begin with a study of the technological characteristics of the enterprise.

The designed system must meet the conditions of reliability and economy, ensure the quality of energy at the consumer, safety, convenience of operation and development. Knowing the manufacturing technology, it is easy and convenient to draw up a power supply scheme for any process unit, line or redistribution. For example: the converter of the main span of the metallurgical plant has many electric receivers (drives of fast and slow turns, conveyor paths, aspiration, etc.); when compiling the diagram, it is not necessary to record these electric receivers from different sections of the same substation, since the disconnection of at least part of the electric receivers will affect the operation of the converter. However, there are electric receivers and technological units, which need to be powered only from independent power sources.

Knowing the dynamics of the development of technological loads, it is necessary to take into account its further development and the possibility of combining with the main scheme. The designed diagrams shall have operational and structural flexibility.

Design Input

Power supply to metallurgical plant

Plant Plot Plan - Figure 1.

About Plant Electrical Loads - Table 1

List of electrical loads of the repair and mechanical workshop (variant of the task is specified by the teacher).

Power can be supplied from a substation of the power system, on which two three-winding transformers with a capacity of 60,000 kV each are installed, with a primary voltage of 110 kV and a secondary voltage of 35, 20, 10, 6 kV.

System capacity 1000 MVA; reactance of the system on the 110 kV side, assigned to the system power, 0.7.

The cost of electricity is 0.8 kop/kWh.

The distance from the power system substation to the plant is 5 km.

Brief description of the plant and electric receivers of the metallurgical plant

At the metallurgical plant, two types of electric furnaces are used for steel smelting: arc and induction (high-frequency). The first of them were more widely used in the metallurgical industry. [4]

Arc furnaces have a capacity of 3-80 tons or more. At metallurgical plants, furnaces with a capacity of 30-80 tons are installed. In electric furnaces, it is possible to obtain very high temperatures (up to 2000 ° C), melt metal with a high concentration of refractory components, have a base slag, clean the metal well from harmful impurities, create a reducing atmosphere or vacuum (induction furnaces) and achieve high deoxidation and degassing of the metal.

Induction furnaces differ from arc furnaces by means of energy supply to molten metal. The induction furnace approximately works in the same way as a conventional transformer: there is a primary coil around which an alternating magnetic field is created when AC is passed. The magnetic flux induces alternating current in the secondary furnace, under the influence of which the metal is heated and melted. Induction furnaces have capacity from 50 kg to 100 t or more.

Nonmagnetic carcass has inductor and refractory melting motor. Furnace inductor is made in form of coil with definite number of turns of copper tube inside which cooling water circulates. The metal is loaded into a crucible which is a secondary winding. Alternating current is generated in machine or lamp generators. Current is supplied from generator to inductor by means of flexible cable or copper buses. The power and frequency of the current are determined by the capacity of the melting crucible and the composition of the charge. Typically, induction furnaces use a current of 500-2500 Hz. Large furnaces operate at lower frequencies. Generator power is selected on the basis of 1.0-1.4 kW/kg of charge. Melting crucibles of furnaces are made of acidic or basic refractory materials.

Forge-stamping machines and presses.

This includes machines for forging and forging metals in hot and cold form in presses used in the manufacture of plastic articles pressed in hot form.

For the production of small parts in the electric industry, electromagnetic presses of 0.5-2 ton are used; in them, the slider is moved using a DC electromagnet that overcomes the action of a spring that normally supports the slider in a raised position. The electromagnet is powered through a semiconductor rectifier.

Cold stamping crank presses with a pressure of 16-4000 tf have a drive power of 2-180 kW; hot stamping - for 630-8000 tf - 28500 kW. The most powerful presses (hydraulic) operate from pump accumulator stations at pressures of 200450 kgf/cm2. This includes hydraulic stamping presses with a force of up to 30000 tf, hydraulic forging presses with a force of up to 100075000 tf. The engines of pump stations of hydropressors are 2501500 kW, and the total capacities of pump stations reach 1012 MW or more. All AC drives 50 Hz, voltage 380, 660, 6000 and 10000 V. The mode of operation is characterized by alternation x.x. with short-term shocks of the shock load, as a result of which flywheels and engines with increased sliding are often used. In some cases, forging machines are equipped with an installation for electrical induction heating or heating of the treated metal with a capacity of up to 400500 kVA. According to the degree of continuity, forging machines and presses belong to 2 categories. The most uninterrupted power supply requires powerful hydropressors that process unique forging - shafts and rotors of large generators, the blanks for which are heated in special furnaces to forging temperature sometimes for several days. For example, an ingot weighing 220 tons for forging a column 23 m long, 900 mm in diameter, 145 tons in a 10,000 tf press is heated before forging for 6 days. The process of forging and stamping is stable, heavy equipment has a permanent location.

The metallurgical plant belongs to consumers of a special category, since the cessation of power supply to production, even for a short period of time, is impossible.

Environmental conditions

Climatic conditions for VL calculation and shall be accepted in accordance with the maps of climatic zoning of Russia and regional maps on wind speed head and ice wall thickness. [7]

The value of the highest air temperature is taken according to actual observations, and the lowest temperature - according to repeatability data 1 times every 5 years.

VL wires should be calculated for normal operation based on different climatic conditions for wind and ice loads.

The following combinations of climatic conditions shall be taken when calculating the HF:

the highest temperature, wind and ice are absent;

low temperature, wind and ice are absent;

wires covered with ice, temperature 5 ° C, no ice;

normal wind speed head qmax, temperature 5 ° С, no ice;

wires are covered with ice, temperature 5 ° C, wind head 0.25qmax (wind speed 0.5Vmax).

Determination of design climatic conditions, intensity of thunderstorm activity and wire dancing for calculation and selection of HF design shall be carried out on the basis of climatic zoning maps with clarification according to regional maps and materials of many observations of hydrometeorological stations and weather posts of hydrometeorological services and power systems for wind speed, intensity of ice-frost deposits and air temperature, thunderstorm activities and beach wires in the area of the constructed route.

When processing these observations, the influence of microclimatic features on the intensity of ice formation and on wind speed as a result of both natural conditions (rough terrain, height above sea level, the presence of large lakes and reservoirs, the degree of vegetation, etc.) and existing or designed engineering structures (dams and watersheds, pond coolers, continuous development strips, etc.) should be taken into account.

The wind head on the support structure is determined taking into account its increase in height. For individual zones with a height of not more than 15 m, the value of the correction factors should be taken constant, determining it by the height of the middle points of the corresponding zones, counted from the ground elevation at the place of installation of the support.

For sections of the VL located in places with strong winds (the high bank of a large river, the upland, valleys and gorges that stand out sharply above the surrounding area, the coastal strip of large lakes and reservoirs within 3-5 km open for strong winds), in the absence of these observations, the maximum speed should be increased by 40% (wind speed - by 18%) compared to the accepted for this area.

The calculated air temperatures are taken to be the same for all voltages for VL according to the data of actual observations and are rounded to values ​ ​ multiple of five.

In certain areas of the territory where there are increased wind speeds during ice or where they can be expected, as well as in areas where a combination of ice-cold deposits is possible, the standard ice values should be taken in accordance with the data on the actual observed ice sizes and wind speed during ice.

VL calculation by emergency operation mode shall be performed for the following combinations of climatic conditions:

average annual temperature te, wind and ice are absent;

lower temperature tmin, no wind and ice;

wires and cables are covered with ice, temperature 5 ° С, no wind;

wires and cables are covered with ice, temperature 5 ° C, wind head 0.25qmax.

The following combinations of climatic conditions shall be taken when calculating the approximations of the current-carrying parts to the elements of the VL supports and structures:

at operating voltage: maximum standard wind speed head qmax, temperature 5 ° С;

at thunderstorms and internal surges: temperature + 15 ° С, wind pressure q = 0.1qmax (V≈0,3Vmax), but not less than 6.25 daN/m2;

to ensure safe lifting to the support under voltage: temperature 15 ° С, wind and ice are absent.

Characteristics of power supply schemes

Intra-plant distribution of electric power is carried out according to the main, radial or mixed "scheme depending on the territorial arrangement of loads, their value, the required degree of reliability of supply. All other things being equal, trunk schemes are used as the most economical. [2]

It is important to provide power for lighting and power loads during the night, on weekends and holidays, if possible without high costs for additional network devices. This task is most successfully solved with single-transformer workshop substations, which for mutual protection of substations are usually connected to each other by low-voltage jumpers designed for power up to 15-30% of the transformer power. This makes it possible to turn off a part of transformers during low loads, which provides an economic effect by reducing power losses and increasing the power factor.

Power distribution schemes within enterprises have a step-by-step construction. In most cases, two or three stages are used, since multi-stage circuits complicate switching and protection. In small enterprises, single-stage power distribution schemes with the use of the second stage are used only for consumers remote from the receiving point.

At the system of deep inputs of PA - 220 kV, the power distribution at the first stage between the SGV is carried out along radial and main air or radial cable lines 35 - 220 kV from the BPU or from the substation of the power system.

When constructing RP, it is necessary to fully use the full

capacity of switching devices: head and section switches. Therefore, RP, as a rule, is advisable with a number of outgoing lines of 6-10 kV of at least eight or ten.

The power distribution scheme is interconnected with the process diagram of the object:

power supply of electric receivers of different parallel process flows is provided from different substation, RP or main lines or from different section of buses of the same substation or RP, so that both process flows do not stop in case of an accident;

within the same flow, all interconnected process units are connected to one source (substation, RP, sections, etc.) so that when the flood is stopped, all electric receivers included in it are simultaneously de-energized;

auxiliary circuits are designed so that their power supply is not disturbed during any switching of power circuits of parallel process flows in order to avoid false disconnections and production shutdown.

Trunk diagrams. In the case of mains, electricity is supplied from the main power unit or power supply center of the enterprise (CHP, GPP) directly to the shop distribution and transformer substations. The number of power distribution and switching links is reduced. This is the main and very significant advantage of these schemes.

The main circuits are suitable for distributed loads, with substations located on the territory of the designed facility, favoring as direct as possible the passage of the highways from the power source to the energy consumers without back-flows of energy and long bypasses. They are most convenient when performing backup of shop substations from another source in case of shutdown of the main supply station.

With trunk circuits, secondary voltage redundancy of adjacent single-transformer substations is not possible, since they are fed along one trunk and simultaneously go out of operation. To eliminate this drawback, closely spaced single-transformer substations are fed from different backbones.

The number of shop transformers fed from one line is usually assumed to be two at the power of transformers 2500 and 1600 kVA; two to three at a power of 1000 kVA; five at a power of 630-250 kVA. The number of thyristor converter transformers of this process line supplied from one line can be taken equal to five to six. With a large number of transformers and a blind connection to the main line, the maximum protection on the head section of the supply line is cut down and may be insensitive during short circuit in this transformer, which may cause the need to install fuses on the branch from the main to the transformer. This makes it possible to selectively disconnect the transformer in case of damage in it.

At large and medium-sized enterprises, 6-35 kV main current wires were widely used. With large electricity flows, cable lines are bulky, difficult to implement, uneconomical, and require a large number of scarce cables. Therefore, at very large energy-intensive enterprises, main current wires are widely used at the first stages of power supply.

Main current conductors 10 and 6 kV have preferential use at currents more than 1.5 - 2 kA. The feasibility of using 35 kV current conductors is determined by technical and economic calculations.

The route of current conductors passes through the areas of placement of main electric loads, in the center of which there are distribution points connected to current conductors. With a successful selection of the route of current conductors, it is possible to provide power from them to about 70-75% of all electrical loads of the enterprise. Consumers remote from the current source route can be fed from remote RP or directly from the GPP. In some cases, conductors can also be used to communicate between two power supplies, which makes the circuit cheaper.

It is often used to connect current wires directly to transformers through separate switches, bypassing the assembly buses of 6-10 kV GPGT. Due to this, the input switches connected to the busbars are unloaded and independent power supply of the current conductors is created, which significantly improves the reliability of the power supply.

Even more rational is the circuit with connection of the current conductor to one of the split windings of the transformer, but it can be used with a uniform distribution of loads between the current conductor and the busbars.

Up to the present time, the circuits of branches from the current conductors, as a rule, were carried out using split (twin) reactors connected to the current conductor through disconnectors, and with the installation of switches after the reactors at the inputs to the RP. However, due to the failure of the reactors while passing the DC current through both windings of the reactor phase, the use of such circuits began to be limited.

Radial power distribution schemes are mainly used when loads are located in different directions from the power center. They can be two-stage or single-stage. Single-stage schemes are mainly used in small enterprises, and two-stage schemes are used in large enterprises .

Figure 4 shows the current distribution of the metallurgical plant, in Figures 5 and 6 the structural and schematic diagram of the power supply, respectively.

List of sources used

Block V.M. Manual for course and degree design for electric power specialties of universities/V.M. Block. - M.: Higher School, 1990.383 p.

Ivannikova N.Y. Methodological guidelines for the course project on the course "Power supply of enterprises and electric drive "/N.Y. Ivannikova. - Murmansk.: MSTU, 2007. – 32 pages.

Kryuchkov I.P., Kuvshinsky N.N., Neklepaev B.N.

Electrical part of power plants and substations: Reference materials for course and degree design. - M.: Energy, 1978.456 p., Il.

Mukoseyev Yu.A. Power supply of industrial enterprises. Textbook for universities/Yu.A. Mukoseev. - M.: "Energy," 1973.584 p. Il.

Electrical Power and Equipment Handbook. In 2 t. - T.1/Under the general. Ed. A.A. Fedorova. - M.: Energoatomizdat, 1986.568 p.

Fyodorov A.A., Starkova L.E. Training manual for course and degree design on power supply to industrial enterprises. - M.: Energoatomizdat, 1987.- 368 s.

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