When designing a power supply network for large consumers, which also includes individual workshops of enterprises, it is important to take into account quite a lot of conditions. The initial data for design depends on many factors, ranging from the specialization of the enterprise to the geographical location, since it is necessary to take into account not only the power consumed by the equipment, but also the costs of lighting and heat supply. A competently and rationally executed workshop power supply project significantly affects the reliability of the installed equipment with the minimum permissible electricity consumption. The power supply of an enterprise must ensure safe working conditions and not have a harmful effect on the environment.

The most complex and time-consuming stage of designing internal power supply is determining and calculating the load power consumption. The calculation is based on data on both the rated power consumption of the equipment and its operating modes. All factors are taken into account, including reactive power, which requires compensation using special equipment - reactive power compensators to ensure a uniform load on the three-phase network.

A separate column in determining the power is the calculation of the workshop lighting system, which allows you to select and optimize the location and types of lamps, depending on the requirements for illumination of various areas. The presence or absence of central heating may require the introduction of seasonal connection of electric heating systems to consumers.

Most industrial workshops require the design of ventilation systems.

These conditions show how labor-intensive it can be to calculate the power supply system at the first stage of design, especially when it comes to power supply to a non-standard equipment workshop.

At the second stage of design, using the data from the first stage and a large-scale equipment placement plan, the type of distribution network is selected. In this case, it is necessary to take into account the following factors:

• Location of electricity receivers on the workshop territory;
• Degree of responsibility of receivers (requirements for power supply reliability);
• Operating mode.

The consumption of power line materials, the location of transformer substations, and distribution boards depend on the chosen distribution network design.

The following types of distribution networks are used:

• Radial schemes;
• Trunk;
• Combined.

With a radial circuit, each receiver is powered from a separate line laid from the distribution board. This type of network is used to connect powerful receivers located at a sufficient distance from one another, and the substation is located near the geometric center of the load.

The main circuit is characterized by the fact that it is used with a concentrated load, when energy receivers are grouped in series and at a short distance from each other. In this case, they are connected to a single main line laid from a transformer substation or distribution board.

A combined circuit includes a main circuit with concentrated loads, when several mains depart from the distribution board, each for its own group of loads. A combined network can also be called a radial construction, when powerful consumers receive power directly from the supply substation, and less powerful ones are combined into groups and receive power from distribution boards.

It is the combined networks that have become most widespread, since they allow the most optimal use of material resources without reducing reliability. At this stage, the receivers’ requirements for power reliability are also taken into account and power supply redundancy schemes are laid out.

The third stage of project development is based on the previous two and involves calculating the required number and power of switchgears, substations, and reactive power compensators.

Calculation of power of electrical energy receivers

The power load on the supply network largely depends on the type of production. For example, the equipment of a metal-cutting machine shop at a metal processing plant, with the same number of devices, consumes much more power than the machines of a wood processing shop. Thus, the power supply of a heavy engineering machine shop requires a more stringent approach regarding the selection of the number and capacity of converter substations and power lines.

When designing, the daily operating schedule of consumers should be taken into account, and calculations should be based on the average power consumption during peak hours. If we take into account the total power of consumers, then most of the time the substation transformers will operate in an underloaded mode, which will lead to unnecessary financial costs for servicing the supply equipment.

It is believed that the optimal operating mode of a transformer should be operation at 65 - 70% of the rated power.

The required cross-section of power supply lines is also selected taking into account the average power consumption, since it is necessary to take into account the permissible current density, heating and power losses.

In the same way, at this stage, the characteristics of the consumption of the reactive component of power must be taken into account for the rational use of compensators. Incorrect placement and parameters of compensators will lead to excessive energy consumption, incorrect metering, and, most importantly, to increased losses and load on power lines.

This task is posed primarily where there are many powerful consumers with inductive loads. The most common example is induction motors, which are found in most machine tools.

Second design stage

The choice of the type of distribution network is partially determined by the characteristics of the equipment according to the category of receivers. There are three categories based on power supply reliability requirements:

1. The first category - a power supply interruption leads to a safety hazard, accidents, and complete disruption of the technological process. This category includes a large number of machine-building and metal-working profile equipment, as well as conveyor-based mass production enterprises, for example, machine-building profiles.
2. The second category is disruption of the production cycle, interruptions in production that do not lead to serious economic consequences. Most industries fall into this category. Here you can specify the equipment of the mechanical repair shop (RMS).
3. The third category includes consumers with more gentle power requirements than the first two categories. This includes most of the production equipment of the sewing workshop, and some metal products workshops.

Equipment belonging to the first category requires designing power supply taking into account the mutual redundancy of several (usually two) sources of external power supply.

The optimal combination of power supply reliability at minimal cost is achieved by the correct choice of power supply system in accordance with the category of equipment and the location of the equipment on the production floor area.

In most cases, the most rational is a combined main circuit with concentrated loads. The equipment of a forge shop or welding shop has its own characteristics in terms of energy consumption and requires the laying of separate supply lines, and the power supply of the machine assembly shop section, on the contrary, can be carried out according to the main circuit. And when several production lines are installed in a workshop, it is impossible to do without several power lines. The same must be taken into account when calculating the power supply of the tool shop.

Separate power lines are laid on the lighting and ventilation system, whether it is an electrical project for a woodworking plant or an electrical project for an aircraft factory of an aviation enterprise.

The final stage

Based on the data from previous calculations, an electrical project is drawn up, consisting of several sets of documents. First, a working design is developed, which can be adjusted during the execution of work depending on local conditions and at the end of the work will differ from the calculated one. One of the main documents when designing power supply is a single-line diagram of the power supply of the workshop. A drawing of a single-line diagram allows you to quickly navigate the intricacies and features of the workshop’s power supply.

Let's sum it up

Designing the power supply system for a separate workshop or an entire plant is one of the most important activities, the implementation of which can only be carried out by specialized organizations authorized to carry out such work. There is no point in wasting time developing a project yourself. No matter how competently and accurately it is carried out, it will still not receive approval from energy sales organizations. By ordering a standard design for an intra-shop power supply scheme for up to 1000 V or more from a licensed organization, you don’t have to worry about the safety and legality of all activities related to the construction and operation of electrical equipment. The finished project will have all the necessary approvals and approvals, starting from a sketch and ending with fully adjusted documentation upon commissioning of the facility.

You can order a project from the Mega.ru company. The company's website contains many articles that reveal the essence and subtleties of design, with examples of projects. Particular attention should be paid to the article, which explains in detail what stages there are in the implementation of an electrical project.

But still, much more information of interest can be obtained by contacting the company directly for advice. The section indicates how you can contact our specialists and get answers to all your questions.

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Introduction

1. General part

1.2 Enterprise structure

1.3 Workshop characteristics

2. Calculation part

2.1 Lighting calculation

2.3 Calculation of short circuit currents

2.4 Selecting equipment

2.5 Calculation of power lines

2.6 Calculation and selection of cable

2.7 Grounding calculation

2.8 Operation and repair of electrical equipment

2.9 Installation of equipment

2.10 Installation of grounding bars of the internal grounding loop

3. Special part

3.1 Description of the electrical equipment of the workshop and substations

3.2 Diagram of stations and substations, their description

3.3 Electroerosive installation, protection of electrical equipment from corrosion

4. Labor protection

4.1 Measures for the safety of equipment operation

4.2 Safety measures during the operation of electrical equipment

4.3 Fire prevention measures

5 Economic part

5.1. Determination of capital costs

5.2 Staff calculation

5.3 Calculation of wage costs, payroll accruals

5.4 Calculation of depreciation costs

5.5 Calculation of electricity costs

5.6 Calculation of material costs

5.7 Calculation of repair costs, commissioning costs, overhead costs, taxes

5.8 Determination of costing for a site (workshop, etc.)

Conclusion

Bibliography

INTRODUCTION

This diploma project will examine the power supply and electrical equipment of the mechanical assembly shop of parts of a medium-sized machine-building plant.

Electricity has been serving people for many decades, and over time the need for it is continuously increasing, which is explained by its advantages over other types of energy: it is easily converted into mechanical, thermal and light energy; relatively easily transmitted over significant distances; the speed of propagation of electricity is approximately equal to the speed of light, and finally, the production and consumption of electricity coincide in time.

In the field of power supply to consumers, the objectives of industrial development, by increasing production efficiency based on accelerating scientific and technological progress, include increasing the level of design developments, introducing and rational operation of highly reliable electrical equipment, reducing non-productive electricity costs during transmission, distribution and consumption.

The development and complication of the structure of power supply systems, increasing requirements for the efficiency and reliability of their operation, combined with the changing structure and nature of electricity consumers, the widespread introduction of devices for controlling the distribution and consumption of electricity based on modern computer technology pose the problem of training highly qualified engineers.

The most important stage in the development of creative activity of future specialists is coursework and diploma design, during which the skills of independent solving of engineering problems and the practical application of theoretical knowledge are developed.

Optimization of production processes in combination with optimization of industrial power supply systems can and should give the country additional funds by reducing unproductive costs

The power supply system is a set of elements designed for the conversion, production, distribution and consumption of electrical energy. Electrical energy is produced by power plants: TPP (thermal power plant), CHP (heat and power plant), HPP (hydro-electric power plant), GRES (hydro-distribution power plant), NPP (nuclear power plant), WPP (wind power plant). In addition to the listed stations, there are also non-traditional methods of obtaining electrical energy, for example: under the influence of the sun, the energy of sea tides, energy obtained as a result of the decay of food waste and environmental plants (organic substances). The power supply of industrial enterprises directly depends on the comprehensive solution of engineering problems. To provide critical equipment with a “clean” guaranteed power supply, it is necessary to use an uninterruptible power supply, which will ensure “continuity” of the voltage sinusoid in the event of an accident in the public network and protect the equipment from all types of electrical interference. Using uninterruptible power supplies, you can ensure reliable power supply to enterprises in any industry. Reliable power supply is an important factor determining the successful functioning of any production.

To ensure uninterrupted power supply, power backup must also be taken into account. Backup power supply allows you to completely eliminate the risks associated with an unexpected power outage in central power grids.

Electrification ensures the fulfillment of the task of widespread comprehensive mechanization and automation of production processes, which makes it possible to increase the growth rate of social labor productivity, improve product quality and facilitate working conditions. Based on the use of electricity, technical re-equipment of industry, the introduction of new technological processes and the implementation of fundamental changes in the organization of production and its management are being carried out. Therefore, in modern technology and equipment of industrial enterprises, the role of electrical equipment is great, i.e. a set of electrical machines, apparatus, instruments and devices through which electrical energy is converted into other types of energy and automation of technological processes is ensured.

Electrical mechanical engineering is one of the leading branches of the mechanical engineering industry. The manufacturing process of an electric machine consists of operations that use a variety of technological equipment. At the same time, the bulk of modern electrical machines are manufactured using mass production methods. The specificity of electrical engineering lies mainly in the presence of processes such as the manufacture and installation of windings of electrical machines, for which non-standardized equipment is used, usually manufactured by the electrical engineering plants themselves.

Electrical mechanical engineering is characterized by a variety of processes that use electricity: foundry, welding, processing of metals and materials by pressure and cutting, heat treatment, etc. Electrical mechanical engineering enterprises are widely equipped with electrified lifting and transport mechanisms, pumping, compressor and fan units.

Modern energy is characterized by increasing centralization of the production and distribution of electricity. To ensure the supply of electricity from power systems to industrial facilities, installations, devices and mechanisms, power supply systems consisting of networks with voltages of up to 1000 V and higher and transformer, converter and distribution substations are used. To transmit electricity over long distances, ultra-long-distance power lines (PTLs) with high voltage are used: 1150 kV AC and 1500 kV DC.

In modern multi-bay workshops of the automotive industry, complete transformer substations (CTS), complete distribution units (KRU), power and lighting busbars, switching, protection, automation, control, metering devices, and so on are widely used. This creates a flexible and reliable power supply system, resulting in significantly reduced costs for power supply to the workshop.

Automation affects not only individual units and auxiliary mechanisms, but increasingly their entire complexes, forming fully automated production lines and workshops.

Of primary importance for production automation are multi-motor electric drives and electrical controls. The development of electric drives follows the path of simplifying mechanical transmissions and bringing electric motors closer to the working parts of machines and mechanisms, as well as the increasing use of electrical speed control of drives.

The purpose of this diploma project is to design the power supply of the mechanical workshop for mechanical assembly of parts No. 9. The main objective of this project is to design a reliable uninterrupted power supply to the workshop receivers with minimal capital and operating costs and ensure high safety.

Power supply systems for industrial enterprises are created to provide electricity to industrial receivers, which include electric motors of various machines and mechanisms, electric furnaces, electrolysis installations, devices and machines for electric welding, lighting installations, etc.

The distribution and consumption system of electricity received from power systems is built in such a way that the basic requirements of electrical receivers located at consumers are met.

Reliability of power supply is achieved through the uninterrupted operation of all elements of the power system and the use of a number of technical devices both in the system and at consumers: relay protection and automation devices, automatic switching on of a reserve, control and alarm. The quality of power supply is determined by maintaining voltage and frequency values ​​at the established level, as well as limiting higher harmonics, non-sinusoidality and voltage asymmetry in the network.

Economical power supply is achieved through the development of advanced power distribution systems, the use of rational designs of complete switchgears and transformer substations, and the development of optimization of the power supply system. The efficiency is influenced by the choice of rational voltages, optimal cross-sections of wires and cables, the number and power of transformer substations, means of reactive power compensation and their placement in the network.

The implementation of these requirements ensures a reduction in costs during the construction and operation of all elements of the power supply system, implementation of this system with high technical and economic indicators, and reliable and high-quality power supply to industrial enterprises.

1. GENERAL PART

1.1 Brief information about the company

Engineering factories consist of separate production units called workshops and various devices.

The composition of the workshops, devices and structures of the plant is determined by the volume of production, the nature of technological processes, requirements for product quality and other production factors, as well as, to a large extent, the degree of specialization of production and cooperation of the plant with other enterprises and related industries.

Specialization involves the concentration of a large volume of output of strictly defined types of products at each enterprise.

Cooperation involves the provision of blanks (castings, forgings, stampings), components, various instruments and devices manufactured at other specialized enterprises.

If the plant being designed will receive castings through cooperation, then it will not include foundries. For example, some machine tool factories receive castings from a specialized foundry that supplies consumers with castings centrally.

The composition of the plant’s energy and sanitary equipment may also vary depending on the possibility of cooperation with other industrial and municipal enterprises in the supply of electricity, gas, steam, compressed air, in terms of transport, water supply, sewerage, etc.

The further development of specialization and, in connection with this, widespread cooperation between enterprises will significantly affect the production structure of factories. In many cases, machine-building plants do not include foundry and forging shops, workshops for the production of fasteners, etc., since blanks, hardware and other parts are supplied by specialized factories. Many mass production factories, in cooperation with specialized factories, can also be supplied with ready-made components and assemblies (mechanisms) for the machines they produce; for example, automobile and tractor factories - finished engines, etc.

1.2 Enterprise structure

The composition of the machine-building plant can be divided into the following groups:

1. Procurement shops (iron foundries, steel foundries, non-ferrous metal foundries, forging shops, forging shops, pressing shops, forging shops, etc.);

2. Processing shops (mechanical, thermal, cold stamping, woodworking, metal coating, assembly, painting, etc.);

3. Auxiliary shops (tool shops, mechanical repair shops, electrical repair shops, model shops, experimental shops, testing shops, etc.);

4. Storage devices (for metal, tools, molding and charge materials, etc.);

5. Energy devices (power plant, combined heat and power plant, compressor and gas generator units);

6. Transport devices;

7. Sanitary installations (heating, ventilation, water supply, sewerage);

8. General plant institutions and devices (central laboratory, technological laboratory, central measurement laboratory, main office, check-out office, medical center, outpatient clinic, communication devices, canteen, etc.).

The production of metalworking equipment, especially machine tools, occupies an important place in mechanical engineering, providing it with the necessary fixed production assets. The production capabilities of mechanical engineering itself, its compliance with modern requirements and the ability to technologically re-equip the entire production and, above all, mechanical engineering, largely depend on the available fleet of machine tools, their proper technological level, and the optimal structure in terms of species composition and significance. The state and technical and technological level of machine tool industry, the structure of the country's metalworking equipment is one of the main indicators of the development of mechanical engineering and its production capabilities.

1.3 Workshop characteristics

The mechanical assembly workshop is designed for the production of food industry equipment.

The workshop is an integral part of the production of a machine-building plant.

The workshop includes production, auxiliary, service and household premises. The workshop receives power supply (ESN) from its own workshop transformer substation (TS) located at a distance of 1.5 km. From the deep input substation (DHS) of the PLANT. Supply voltage 6,10 or 35 kV.

The PGW is connected to the power grid (ENS), located at a distance of 8 km. EE consumers belong to ESN reliability categories 2 and 3. Number of work shifts: 2. The soil in the workshop area is clay with a temperature of +50C. The building frame is constructed from blocks - sections 6 and 8 m long each. Dimensions of the plot: АхВхН=52х36х10m. All rooms, except the machine room, are two-story.

Table 1 - List of workshop equipment

Posted on http://www.allbest.ru/

1.4 Existing power supply scheme

To distribute electrical energy within the workshops of industrial enterprises, electrical networks with voltages of up to 1000V are used.

The layout of the intra-shop network is determined by the technological process of production, the layout of the workshop premises, the relative location of the electric power supply, transformer transformer and power inputs, the design power, the requirements for uninterrupted power supply, environmental conditions, and technical and economic considerations.

The power supply of the workshop's electrical equipment is usually carried out from the workshop's transformer substation or the transformer substation of a neighboring workshop.

Intrashop networks are divided into:

· nourishing

· distribution.

The supply networks extend from the central distribution board of the workshop transformer substation to the power distribution cabinets of the joint venture, to the ShRA distribution busbars or to individual large electric power distribution units. In some cases, the supply network is carried out according to the BTM (Block - Transformer - Main) scheme.

Distribution networks are networks that go from power distribution cabinets or busbars directly to the electric power supply. In this case, the electric power supply is connected to the distribution devices by a separate line. It is allowed to connect up to 3-4 electrical units with a power of up to 3 kV in one line, connected in a chain.

In their structure, the schemes can be radial, mainline and mixed.

Radial schemes using SP are used in the presence of concentrated loads with their uneven distribution over the workshop area, as well as in explosion- and fire-hazardous workshops, in workshops with a chemically active and dusty environment. They are highly reliable and are used to power electrical devices of any category. Networks are made by cables or insulated wires.

It is advisable to use main circuits to power distribution loads relatively evenly over the workshop area, as well as to power groups of electrical equipment belonging to the same production line. The circuits are made using busbars or cables. In a normal environment, complex busbar trunking systems can be used to build backbone networks.

1.5 Selecting a power supply scheme

An important technical problem that needs to be solved when designing power supply is the choice of voltage for the power and lighting networks. Voltage losses, electricity losses and many other factors will depend on the correct choice. The choice of voltage is based on a comparison of the technical and economic indicators of various options. When choosing a voltage to supply power and lighting consumers, preference should be given to the option with a higher voltage, since the larger the U value, the lower the current in the wires, the smaller the cross-section, and the less power and energy losses.

The choice of power supply circuit for workshop receivers depends on many factors:

· power of individual consumers;

· location of consumers;

· workshop area;

· technological process of the workshop, which determines the category of power receivers based on uninterrupted power supply.

The power supply system must meet the following requirements:

· convenience and reliability of service;

· proper quality of electricity;

· uninterrupted and reliable power supply both in normal and emergency modes;

· efficiency of the system, that is, the lowest capital costs and operating costs;

· flexibility of the system, that is, the ability to expand production without significant additional costs.

To transmit and distribute electricity to workshop consumers, we use the most advanced “transformer - main line” block diagram, which reduces the cost and simplifies the construction of a workshop substation. Such schemes are very common and provide system flexibility and reliability, as well as cost-effectiveness in material consumption.

For the designed workshop we use a three-phase alternating current system with a voltage of 380/220 V with a solidly grounded neutral, which allows power and lighting loads to be powered from the same transformers. Power consumers are powered by a voltage of 380 V, and lighting by a voltage of 220 V. According to the requirements of Safety Engineering, the control circuits and local lighting are powered by reduced voltage: The control circuits are powered by a voltage of 110 V, lighting by 12 V or 24.

When powering the power and lighting networks from a single transformer transformer substations, the lights of the lighting fixtures flicker, as powerful motors start and large inrush currents arise. Therefore, power is supplied from two transformer transformer substations. Power receivers with large and frequent peak loads need to be connected to one of the KTP transformers, and a “quieter” load to another transformer. In this case, work lighting must be powered from a transformer with a “quiet” load, and emergency lighting from a transformer with a “unquiet” load, in order to ensure proper quality of work lighting.

2. CALCULATION PART

2.1 Lighting calculation

The illuminated volume of the room is limited by enclosing surfaces that reflect a significant part of the light flux incident on them from light sources. In indoor lighting installations, reflective surfaces include the floor, walls, ceiling and equipment installed in the room. In cases where the surfaces enclosing the space have high reflectance values, the reflected component of illumination can also be of great importance and its consideration is necessary, since reflected fluxes can be comparable to direct fluxes and their underestimation can lead to significant errors in calculations.

In the process of performing the calculation part it is necessary:

a) select a lighting system, light source, type of lamp for a given area or workroom;

b) calculate the general lighting of the working area.

The purpose of calculating general lighting is to determine the number of lamps necessary to ensure Emin and the power of the lighting installation necessary to ensure normal illumination in the workshop. Below we consider the calculation of general lighting using the luminous flux utilization coefficient method.

When calculating using this method, the required luminous flux of one lamp is determined by the formula:

or number of lamps:

where Emin is the minimum standardized illumination, lux;

k - safety factor (for incandescent lamps k=1.15, for fluorescent and DRL lamps,

S - illuminated area, m2;

Z - minimum illumination coefficient (lighting unevenness coefficient) (when calculating lighting from lamps with incandescent lamps and DRL Z = 1.15)

N - number of lamps;

n is the number of lamps in the lamp;

h is the luminous flux utilization factor in fractions of unity.

The power of the lighting installation P is determined from the expression:

Where: Pi is the power consumption of one lamp, kW.

1.Choose a lighting system.

2. Justify the standardized illumination at workplaces of a given object.

3. Choose an economical light source.

4. Choose a rational type of lamp.

5. Estimate the illumination safety factor, k, and the illumination unevenness coefficient, Z.

6. Estimate the reflection coefficients of surfaces in the room (ceiling, walls, floor), r.

8. Find the luminous flux utilization factor, h.

10. Draw a sketch of the location of the lamps on the floor plan, indicating the dimensions.

Principles for selecting the main elements necessary for calculation

Selecting a lighting system:

This work considers only work lighting, which can be general or combined. The installation of only local lighting in production premises is prohibited.

The choice of lighting system depends, first of all, on such an important factor as the accuracy of the visual work performed (the smallest size of the object of discrimination); according to current standards, when performing work of categories I - IV, a combined lighting system should be used. In mechanical, instrumental, assembly, etc., as a rule, a combined lighting system is used. The choice of lighting system is made simultaneously with the choice of normalized illumination.

Selection of normalized illumination:

Quantitative and qualitative indicators of artificial lighting are determined in accordance with current standards.

As a quantitative characteristic of illumination, the lowest illumination of the working surface Emin is taken, which depends on the category of visual work, the background and contrast of the object with the background and the lighting system. The category of visual work is determined by the minimum size of the object of discrimination, i.e. the size of an object, its part or a defect on it that needs to be detected or distinguished during production activities.

Qualitative indicators of lighting (pulsation coefficient and glare index) are not considered in this work.

You can take the Emin value for precision work of the III category 300-500 lux, for medium precision IV category 150-300 lux, for low-precision work V category 100-150 lux. A lower illumination value in each digit for a light background and high contrast, a higher value for a dark background and low contrast.

The determining parameters when choosing an economical light source are construction parameters, architectural and planning solutions, air condition, design issues and economic considerations.

When designing lighting, the designer always makes a compromise decision.

Incandescent lamps are low-cost, have a light output of 7-26 lm/W, they have a distorted emission spectrum, and become very hot during operation. But, on the other hand, they are low cost, easy to operate and can be recommended for premises with temporary occupancy, household premises, etc.

In industrial premises with a height of up to 7 - 12 m, it is advisable to use DRL type lamps, because they are more powerful and have greater light output up to 90 lm/W.

The final choice of a light source must be made simultaneously with the choice of the type of luminaire of which it is a part.

The choice of general lighting fixtures is made based on lighting technical, economic requirements, and air conditions. There is a classification of lamps according to light distribution: direct, predominantly direct, diffused, predominantly reflected and reflective light.

In addition, there are lamps with different luminous intensity curves: concentrated, deep, cosine, semi-wide, wide, uniform and sine.

According to GOST 14254-69, lamps are classified according to the degree of protection from dust, water and explosion.

Based on their design, there are 7 operational groups of luminaires. Due to the extreme variety of luminaires, the specific choice of luminaire should be decided jointly with energy specialists, economists, designers and taking into account occupational safety requirements.

The safety factor k takes into account dust in the room and a decrease in the luminous flux of lamps during operation. The values ​​of the coefficient k are given in the table.

Table 2 Values ​​of coefficient k

The minimum illumination coefficient Z characterizes the unevenness of illumination. It is a function of many variables, its exact determination is difficult, but to the greatest extent it depends on the ratio of the distance between the luminaires to the design height (L / h).

Choose a method for placing lamps, which can be symmetrical or localized. With symmetrical placement, the lamps are located both along and across the room at the same distance, at the corners of a rectangle or in a checkerboard pattern. Symmetrical placement of lamps provides equal illumination of equipment, machines, workplaces and passages, but requires high power consumption. With a localized arrangement, luminaires are placed taking into account the location of machines, machines, equipment, control points and workplaces. This arrangement of lamps, which reduces energy consumption, is used in workshops with asymmetrical placement of equipment.

Next, determine the ratio of the distance between the lamps L to the height of their suspension h. Depending on the type of lamp, this ratio L / h when the lamps are arranged in a rectangle can be taken equal to 1.4-2.0, and when the lamps are arranged in a checkerboard pattern -1.7-2.5.

The height of the lamp above the illuminated surface

Hc=H - hcв - hp (4)

where: H - total height of the room, m;

hcв - height from the ceiling to the bottom of the lamp, m;

hр - height from the floor to the illuminated surface, m.

To reduce the glare of general lighting lamps, their suspension height above the floor level is set to at least 2.5-4 m for lamps with a power of up to 200 W and at least 3-6 m for lamps of higher power.

Required number of luminaires (lamp) n= S/LI (with La = Lb).

When placing lamps in a line (row), if the most favorable L/h ratio is maintained, it is recommended to take Z = 1.15 for incandescent lamps and DRLs.

Fig. 1 Layout of lamps in the room

To determine the utilization factor of the luminous flux h, find the room index i and the expected reflection coefficients of the room surfaces: ceiling rп, walls rс, floor rр.

For dusty production areas:

The room index is determined by the following expression:

where: A, B, h - length, width and estimated height (height of the lamp hanging above the working surface) of the room, m.

where: H - geometric height of the room;

hsv - overhang of the lamp.

Typically: hsv = 0.2 ...0.8 m;

hp - height of the working surface.

hp = 0.8 ...1.0 m.

The luminous flux utilization coefficient is a complex function, depending on the type of lamp, room index, reflectance of the ceiling, walls and floor.

Intermediate values ​​of the utilization factor are found by interpolation.

For a given Fl, i.e. we know which lamps will be used, find N, i.e. how many lamps need to be used.

Given N or n, we determine Fl. Based on the found FL, the nearest standard lamp is selected within the tolerance limits of 10 +20%.

Table 3 Value of utilization factor h for luminaires with fluorescent lamps, %

An example of calculating a room using the utilization coefficient method

Example. In a room with dimensions A=52 m, B=36 m, H=10 m, hp=0.9 m and the reflection coefficients of the ceiling rп=30%, walls rc=10%, design surface рр=10% are determined by the utilization coefficient method luminous flux lighting with Astra lamps with incandescent lamps to create illumination E = 50 lux.

Solution. In a room with low dust emissions, a lighting installation with incandescent lamps is calculated with a safety factor of k = 1.15. The Astra lamp has cosine light distribution. Therefore, the optimal relative distance between lamps should be taken l = 1.6. Taking the light height of the lamps hcв = 0.5 m, we obtain the estimated height

hр=10-0.9-0.5=8.6 m

and distance between lamps

L=8.6 H 1.6=13.76 m.

Number of rows of lamps in the room

Nb=36/13.76=2.6.

Number of lamps in a row

Na=52/13.76=3.77.

We round these numbers to the nearest larger ones Na=4 and Nb=3.

Total number of luminaires

N= Na × Nb=4 × 3=12. (7)

We finally place the lamps.

Along the width of the room, the distance between the rows is Lb = 3.77 m, and the distance from the outer row to the wall is slightly more than 0.3 L, namely 1.13 m. In each row, the distance between the lamps we also take La = 13.76 m, and the distance from the outermost lamp to the wall there will be:

This amounts to 0.28 L=3.85

Room index

i=52 H 36/=1872/(8.6 H 88)=2.47.

Using the reference book, we select the luminous flux utilization factor з=0.6. Since the distance between the lamps is almost equal to the optimal one, we accept the minimum illumination coefficient z = 1.15. Determine the required luminous flux of the lamp

Fl = 50 H 1.15 H 1872 H 1.15/(12 H 0.6) = 17192.5 lm

We select from the table the nearest standard DRL 250 lamp having a flux Fl = 11000 lm, which is less than the calculated value

DF=(11000-17192.5)100/17192.5= - 3.6%.

2.2 Calculation of loads and selection of power transformer

When determining design electrical loads, you can use the following basic methods:

1. ordered diagrams (maximum coefficient method);

2. specific electricity consumption per unit of production;

3. demand coefficient;

4. specific density of electrical load per 1 m2 of production area.

The calculation of expected loads is carried out using the method of ordered diagrams, which is currently the main method in the development of technical and operational power supply projects.

The estimated maximum power of electrical receivers is determined from the expression:

Pmax=Kmax * Ki * Pnom = Kmax * Pcm, (8)

where: Ki - utilization factor;

Kmax - maximum active power coefficient;

Pcm is the average active power of electrical receivers for a more loaded circuit.

Determine the planned working time fund for the analyzed period, taking into account the established operating mode. To calculate it, you can use the production time sheet-calendar if the enterprise operates on a five-day work week. If shifts are established in production, then the planned working hours are calculated based on the approved shift schedules. In this example, the planned load of one machine for a month will be equal to: 30 days per 24 hours = 720 hours.

We determine the number of hours of actual operation of machines in the workshop for the period. To do this, we need timesheet data. Let's find the total number of hours worked by the workshop personnel. Let the workers of the mechanical assembly shop work 14,784 man-hours in a month, which corresponds to the actual operating time of the machines.

Let's calculate the utilization rate of weaving shop equipment using the formula:

Ki= (Fr/S)/Fp, (9)

where: Фр - actual amount of time worked by all machines, hour,

C - number of machines in the workshop, pcs.

Fp - planned working time fund, hour.

In this example, the equipment utilization rate will be equal to:

14784/42/720 = 0,5.

Consequently, the looms of the weaving workshop were used at 50% per month. The remaining 50% is his downtime.

For a group of electrical receivers for a busier shift of operating mode, the average active and reactive loads are determined by the formula:

Pcm = Ku * Pnom (10)

Qcm = Pcm * tan c, (11)

where tg c corresponds to the weighted average cos c for electrical receivers of a given operating mode.

The weighted average utilization rate is determined by the formula:

KU.SR.VZ. = ?Рсм / ?Рном, (12)

where? Рсм is the total power of electrical receivers and groups for the busiest shift;

Rnom - the total rated power of electrical receivers in the group.

The relative number of electrical receivers is determined by the formula:

where n1 is the number of large receivers in the group;

n is the number of all receivers in the group.

The relative power of the largest power receivers is determined from the expression:

P* = ?Pn 1/?Pnom, (14)

where?Pn 1 is the total active rated power of large electrical receivers of the group;

Rnom - the total active rated power of the group's electrical receivers.

The main effective number of electrical receivers in a group is determined from reference tables based on the values ​​of n* and P*

n*e = f(n*; P*) (15)

The effective number of power receivers in a group is determined by the formula:

Ne = n*e * n (16)

The maximum coefficient is determined from reference tables, based on the values ​​of ne and KU.SR.VZ.:

Kmax = f(Ne; KU.SR.VZ.) (17)

Estimated maximum active circuit power:

Rmax = Kmax * ?Рcm (18)

Estimated maximum reactive power in the circuit:

Qmax = 1.1 ?Qcm (19)

The total design power of the group is determined by the formula:

Smax = vPmax2 + Qmax2 (20)

The maximum rated current of the group is determined by the formula:

Imax = Smax/(v3 * Unom) (21)

Calculation of expected loads in a metal-cutting machine shop.

1. Determine the average active and reactive power for a more loaded circuit of electrical receivers.

Calculation example for machines positions 1-3

Rcm1-3 = Rnom Ch Ki = 3 Ch 0.5 Ch 3 = 4.5 kW (22)

Qcm1-3 = Рсм1-3 Х tgts = 4.5 Х 0.75 = 3.4 kVAr (23)

The rest of the calculation data is presented in Table 5

2. Determine the total power for the group:

Pnom = 3Pcm1-3 + 2Pcm4.5 + 2Pcm6.7 + 4Pcm8-11 + 2Pcm12-13+ 8Pcm14-21 + 3Pcm22-24 + 2Pcm25-26 + 1Pcm27 + 4Pcm28-31+ 3Pcm32-34 + 2Pcm35-36 + 2Pcm37- 38+ 1Pcm39 + 2Pcm40-41 + 1Pcm42 + 6Pcm43-48 + 2Pcm 49-50 = 216.5 kW (24)

3. Let’s sum up the active and reactive loads:

Pcm = Pcm1-3 + Pcm4.5 + Pcm6.7 + Pcm8-11 + Pcm12-13+ Pcm14-21 + Pcm22-24 + Pcm25-26 + Pcm27 + Pcm28-31+ Pcm32-34 + Pcm35-36 + Pcm37- 38+ Pcm39 + Pcm40-41 + Pcm42 + Pcm43-48 + Pcm 49-50 = 108.25 kW (25)

Qcm = Qcm1-3 + Qcm4.5 + Qcm6.7 + Qcm8-11 + Qcm12-13+ Qcm14-21 + Qcm22-24 + Qcm25-26 + Qcm27 + Qcm28-31+ Qcm32-34 + Qcm35-36 + Qcm37- 38+ Qcm39 + Qcm40-41 + Qcm42 + Qcm43-48 + Qcm 49-50 = 81.21 kVAr. (26)

4. Determine the weighted average value of the utilization factor:

Ki.av.vz = 108.25 /216.5 = 0.5

5. Determine the relative number of electrical receivers:

N* = 12/42 = 0.3

6. Determine the relative power of the largest power receivers:

P* = 119/216.5 = 0.55 kW

7. The main effective number of electrical receivers in a group is determined based on the values ​​of N* and P*:

8. Determine the effective number of electrical receivers in the group:

Ne = 0.68 H 42 = 28.56

9. The maximum coefficient Kmax is used to transition from average load to maximum. The maximum active power factor is determined based on the values ​​of ne and Ki.av.in:

10. Determine the estimated maximum active power of the circuit:

Rmax = 0.51 H 108.25 = 55.21 kW

11. Determine the estimated maximum reactive power of the circuit:

Qmax = 1.1 H 81.21 = 89.33 kVAr

12. Determine the total design capacity of the group:

13. Determine the maximum rated current of the group:

Imax = 105.01/(1.73 H 0.38) = 159.7 A

Table 5 Summary of electrical power loads in the workshop

The choice of the number and power of power transformers for the main step-down substations (MSS) of industrial enterprises must be technically and economically justified, since this has a significant impact on the rational design of industrial power supply schemes. When choosing the number and power of power transformers, the technique of technical and economic calculations is used, and also takes into account such indicators as the reliability of power supply to consumers, non-ferrous metal consumption and required transformer power. For ease of operation of industrial power supply systems, they strive to use no more than two or three standard transformer capacities, which leads to a reduction in the warehouse reserve and facilitates the interchangeability of transformers. It is desirable to install transformers of the same power, but such a solution is not always feasible. The selection of transformers should be made taking into account the electrical connection diagrams of substations, which have a significant impact on capital investments and annual costs of the power supply system as a whole, and determine its operational and operating characteristics.

In order to reduce the cost of substations (GPP or GRP) with a voltage of 35 - 220 kV, circuits without installing switches on the higher voltage side (according to the line-transformer block diagram), shown in Fig. 1. Shop transformers, as a rule, should not have a switchgear on the high voltage side (Fig. 2). Direct (blind) connection of the supply cable to the transformer should be widely used for radial power supply circuits of the transformer (Fig. 2, a) or connection through a disconnector or load switch for main power supply circuits (Fig. 2.6, c, d). In the main power supply circuit of a transformer with a power of 1000 kVA and above, a load switch is installed instead of a disconnector, since at a voltage of 6 - 20 kV the disconnector can disconnect XX transformers with a power of no more than 630 kVA. Currently, newly constructed workshop transformer substations are completed as complete units (KTP ), completely manufactured in factories and large blocks mounted at industrial enterprises.

Rice. 2 Structurally, workshop transformer substations (TS) are divided into intra-shop ones, which are located in multi-bay workshops; built into the workshop circuit, but with transformers rolled out; attached to the building; separately located on the territory of enterprises, which are used when it is impossible to locate in-shop, built-in or attached substations due to production conditions.

Rice. 3. Basic connection diagrams for workshop TS with higher voltage 6 - 20 kV: a - blind connection; b, c, d - connection of TP through switching devices (VN - load switch, R - disconnector, VNP - load switch with fuse)

The choice of the number of transformers is related to the operating mode of the station or substation. The load schedule may be such that, for economic reasons, it is necessary to install not one, but two transformers. Such cases, as a rule, occur when the load graph fill factor is poor (0.5 and below). In this case, the installation of disconnecting devices is necessary for operational actions (performed by personnel on duty or occurring automatically) with power transformers while observing the economically feasible mode of their operation. The important factors that most significantly influence the choice of the rated power of a transformer and, therefore, its economically feasible mode of operation are the temperature of the cooling medium at the place of its installation and the load schedule of the consumer (load changes during the day, week, month, season and year).

The type of transformers is selected taking into account the conditions of their installation, ambient temperature, etc. Two-winding transformers are mainly used in industrial enterprises. Three-winding transformers 110/35/6 - 20 kV at the gas production point are used only if there are remote consumers of average power related to this enterprise. Transformers with split windings 110/10-10 kV or 110/6-10 kV are used in enterprises with voltages of 6 and 10 kV when it is necessary to reduce the short-circuit current and provide power to shock loads.

Rice. 4. Single-line diagrams of electrical connections of a GPP with two transformers without switches on the high voltage side: a -- with short circuiters and separators; b - only with short circuiters; c -- with disconnectors and fuses of the PSN type.

GPP transformers with a voltage of 35 - 220 kV are manufactured only with oil cooling and are usually installed outdoors. For workshop transformers with a higher voltage of 6 - 20 kV, oil transformers of the TM, TMN, TMZ types, dry transformers of the TSZ type (with natural air cooling) and transformers of the TNZ type with non-flammable liquid (Sovtol) are used. Oil transformers of workshop transformer substations with power SHOM.T «S< 2500 кВ * А устанавливают на открытом воздухе и внутри зданий. Внутрицеховые ТП, в том числе и КТП, применяют только в цехах I и II степени огнестойкости с нормальной окружающей средой (категории Г и Д по противопожарным нормам). Число масляных трансформаторов на внутрицеховых подстанциях не должно быть более трех. Мощность открыто установленной КТП с масляными трансформаторами допускают до 2 х 1600 кВА. При установке на втором этаже здания допустимая мощность внутрицеховой подстанции должна быть не более 1000 кВ * А. Сухие трансформаторы мощностью SH0M T sg 1000 кВ- А применяют для установки внутри административных и общественных зданий, в лабораториях и других помещениях, к которым предъявляют повышенные требования в отношении пожаробезопасности (некоторые текстильные предприятия и т. п.). Сухие трансформаторы небольшой мощности (10 -- 400 кВА) размещают на колоннах, балках, фермах, так как они не требуют маслосборных устройств. Трансформаторы (совтоловые) типа ТНЗ предназначены для установки внутри цехов, где недопустима открытая установка масляных трансформаторов. Герметизированные совтоловые трансформаторы не требуют в условиях эксплуатации ни ревизии, ни ремонта. Их ремонт и ревизию производят на заводах-изготовителях.

The main requirements when choosing the number of transformers for state substations and shop transformer substations are: reliability of power supply to consumers (taking into account the category of electricity receivers in relation to the required reliability), as well as the minimum reduced costs for transformers, taking into account the dynamics of growth of electrical loads.

When designing a substation, the requirements are taken into account based on the following basic provisions. Reliability of power supply to category I consumers is achieved due to the presence of two independent power sources, while ensuring power backup for all other consumers. When supplying category I consumers from one substation, it is necessary to have at least one transformer on each bus section, and the power of the transformers is selected so that if one of them fails, the second (taking into account the permissible overload) will provide power to all category I consumers. Backup power supply for category I consumers is introduced automatically. Category II consumers are provided with a reserve entered automatically or by the actions of on-duty personnel. When powering these consumers from one substation, you should have two transformers or a warehouse backup transformer for several substations feeding category II consumers, provided that the transformer can be replaced within a few hours. During the replacement of the transformer, restrictions are introduced on the power supply to consumers, taking into account the permissible overload of the transformer remaining in operation. Consumers of category III receive power from a single-transformer substation in the presence of a “warehouse” backup transformer.

When choosing the number of transformers, it is assumed that the construction of single-transformer substations does not always provide the lowest costs. If, under the conditions of consumer power backup, it is necessary to install more than one transformer, then they strive to ensure that the number of transformers at the substation does not exceed two. Two-transformer substations are more economically feasible than substations with one or more transformers. When constructing two-transformer GPP substations, the simplest electrical connection scheme on the higher voltage side is chosen. All other solutions (substations with three or more transformers) are usually more expensive. However, they may be necessary when it is necessary to build substations to supply consumers requiring different voltages. Main step-down substations, deep bushing substations (DHS) and workshop transformer substations are made with no more than two transformers. For consumers of III and partially II categories, the option of installing one transformer with backup power from an adjacent transformer substation is being considered. In this case, the backup substation is the second substation and must have power reserve. At workshop substations with two transformers, it is advisable to keep the working sections of low-voltage busbars in operation separately. In this mode, the short-circuit current is reduced by 2 times and the operating conditions for devices with voltages up to 1 kV are simplified. When one operating transformer is disconnected, the second one takes over the load of the sectional circuit breaker that was disconnected as a result of turning on.
Currently, workshop TPs are completed as complete units (KTP). Correct determination of the number of transformer substations and the power of transformers on them is possible only on the basis of technical and economic calculations (TEC), taking into account compensation of reactive loads at voltages up to 1 kV. The number of workshop transformers varies from the minimum possible Nmm (with full compensation of reactive loads) to the maximum Nmax (in the absence of compensating devices) with the average value of the load factor Kt T for all transformer substations. At two-transformer workshop substations with a predominance of loads of category I K-,. , taken within 0.65 - 0.7; with a predominance of loads of category II 0.7--0.8, and with loads of category III 0.9 - 0.95. The minimum and maximum number of workshop transformers are determined by the expressions

where: Pmax, Smax - design load of the workshop; SHom,t is the rated power of the workshop transformer.

A change in the number of workshop transformers (at t = const) leads to a change in the reduced costs for switchgear 6 - 20 kV, for workshop networks 0.4 kV, for distribution networks 6-20 kV. When choosing the number of transformers at workshop transformer substations, it is taken into account that the maximum power of transformers currently manufactured by manufacturers for a voltage of 0.4-0.66 kV is 2500 kVA.

The power of power transformers under normal conditions should provide power to all power receivers of industrial enterprises. The power of power transformers is selected taking into account the economically feasible mode of operation and the corresponding provision of power backup for consumers when one transformer is turned off and the fact that the load of transformers under normal conditions should not (due to heating) cause a reduction in its natural service life. The country's industrial enterprises are increasing their production capacity through the construction of new workshops, the development of new or more rational use of existing areas. Therefore, they provide for the possibility of expanding substations by replacing installed transformers with more powerful ones. In this regard, the equipment and busbars in transformer circuits are selected according to design parameters, taking into account the future installation of transformers with the next rated power on the GOST scale. For example, if two transformers with a capacity of 16,000 kV A are installed at a substation, then their foundations and structures provide for the installation of two transformers with a capacity of 25,000 kV * A without significant alterations to the substation.

Similar documents

Calculation of workshop electrical loads using the maximum coefficient method. Selecting the cross-section and brand of wires. Determination of short circuit currents and grounding devices. Arrangements for organizing electrical installation work. Directions for the development of capital construction.

course work, added 04/18/2011


Power supply system for metallurgical enterprises. Main equipment at the substation. Characteristics of operating electrical equipment. Calculation of short circuit currents in the network. Calculation and selection of switching devices and power transformer.

course work, added 05/08/2013


Power supply for the mechanical repair shop. Buffer nitrogen compression installation. Calculation of electrical loads of power supply systems. Selecting the number and power of transformers. Calculation of short circuit currents and relay protection of a power transformer.

training manual, added 01/15/2012


Development of a power supply diagram for an industrial enterprise. Calculation of electrical loads and short circuit currents. Determination of the number and power of transformers. Selection of high-voltage electrical equipment, protection devices and grounding devices.

course work, added 04/16/2014


Calculation of electrical loads. Selecting a power supply and voltage scheme. Calculation and selection of transformer power. Calculation of short circuit currents. Relay protection of power transformer. Calculation of protective grounding. Overvoltage and lightning protection.

thesis, added 02/20/2015


Characteristics of the installation area of ​​the electromechanical workshop. Calculation of electrical loads, lighting, power losses in the transformer, short circuit currents. Selection of elements of supply and distribution networks. Calculation of the grounding device.

course work, added 11/24/2014


Operation, testing, maintenance, repair and disposal of power transformer. Calculation of the life curve of electrical equipment and grounding devices for personnel protection. Organization of construction, electrical installation and commissioning works.

course work, added 04/10/2012


Detailed development of power supply for the ZRDT "KEC" workshop. Determination of overhead power line loads, rated currents and short circuit currents. Selection of electrical equipment for a step-down substation. Calculation of grounding and lightning protection scheme.

thesis, added 07/07/2015


Calculation of short circuit currents for selecting and checking electrical equipment parameters and relay protection settings. Characteristics of electricity consumers. Selecting the number and power of power transformers. Calculation of power and lighting loads of the workshop.

test, added 11/23/2014


General characteristics of the workshop building and electricity consumers. Electrical load analysis. Calculation and selection of a compensating device, power of transformers, networks, protection devices, high-voltage electrical equipment and grounding devices.

Power supply of mechanical shop section No. 19

Coursework

Energy

Shop power distribution networks must: ensure the necessary reliability of power supply to power receivers depending on their category; be convenient and safe to use; have optimal technical and economic indicators with a minimum of reduced costs...

MINISTRY OF EDUCATION AND SCIENCE OF RUSSIA

Orsk Institute of Humanities and Technology (branch)

federal state budgetary educational institution

higher professional education

"Orenburg State University"

(Orsk Institute of Humanities and Technology (branch) of OSU)

Faculty of Mechanics and Technology

Department of Electric Power and Electrical Engineering

COURSE PROJECT

in the discipline "Power supply of enterprises and electric drive"

Power supply of mechanical shop section No. 19

Explanatory note

OGTI 140106. 65 6 4. 14. 019 PZ

Supervisor

Ph.D. tech. sciences

Davydkin M.N.

"___"______________2014

Executor

Student gr. 10EOP

Saenko D.A.

"___"______________2014

Orsk 2014

Task………………………………………………………………………………………3

Abstract………………………………………………………………………………..5

Introduction……………………………………………………………………………………….6

1. Brief description of the electrical receivers of the workshop……………………….…..8

2. Selection and justification of the workshop power supply scheme…………………….…9

3. Calculation of electrical loads of the workshop area……………………………..10

4. Selection of brand and cross-section of live parts (wires, cables,

busbars)……………………………………………………………….…16

5. Selection of switching and protective equipment……………………………18

6. Selection of power of workshop substation transformers. Compensation

reactive power…………………………………………………………….....21

7. Calculation of the 10 kV supply line…………………………………………………………...25

8. Structural implementation of the workshop network…………………………………..31

Conclusion…………………………………………………………………………………33

List of sources used……………………………………… ….34

Exercise

Topic: Power supply of the machine shop area.

Option 19

1. 2 transformers of the TMN 10000/110 brand are installed at the GPP.
2. The distance from the main production point to the workshop is 0.6 km; from the gas station to the power system substation is 12 km.
3. Short circuit power on 110 kV busbars of a power system substation S k = 1500 MVA.

Introduction

A power supply system (PSS) is a set of devices for the production, transmission and distribution of electricity. Power supply systems for industrial enterprises are created to provide power to industrial receivers, which include electric motors of various machines and mechanisms, electric furnaces, electrolysis installations, devices and machines for electric welding, lighting installations, etc.

Currently, most consumers receive electricity from power grids.

As electricity consumption develops, power supply systems for industrial enterprises become more complex. They include high-voltage networks, distribution networks, and in some cases, industrial CHP networks.

On the way from the power source to electrical receivers in modern industrial enterprises, electrical energy is usually transformed one or more times. Depending on their location in the power supply diagram, transformer substations are called main step-down substations or workshop transformer substations.

Shop electrical distribution networks must:

• ensure the necessary reliability of power supply to electricity receivers depending on their category;
• be convenient and safe to use;
• have optimal technical and economic indicators (minimum reduced costs);
• have a design that ensures the use of industrial and high-speed installation methods

For receiving and distributing electricity to consumer groups

Three-phase alternating current of industrial frequency with a voltage of 380 V is used in power distribution cabinets and points.

The main problem in the near future will be the creation of rational power supply systems for industrial enterprises, which is associated with the following:

• selection and application of a rational number of transformations (the optimal number of transformations is two or three);
• selection and use of rational voltages (in power supply systems of industrial enterprises provides significant savings in electricity losses);
• correct choice of location for workshop and main distribution (step-down) substations (provides minimum annual levelized costs);
• further improvement of the methodology for determining electrical loads (contributes to solving the general problem of optimizing the construction of in-plant power supply systems);
• rational choice of the number and power of transformers, as well as power supply circuits and their parameters, which leads to a reduction in electricity losses and increased reliability;
• a fundamentally new formulation for solving problems such as, for example, symmetry (leveling) of electrical loads.

1. Brief description of the electrical receivers of the workshop.

When determining the electrical loads of existing or planned industrial enterprises, it is necessary to take into account the operating mode, power, voltage, type of current and reliability of power supply of electrical receivers.

According to their operating mode, electrical receivers can be divided into three groups:

with long-term operation;

with intermittent operation;

with short-term operating mode.

Heating furnaces and drying cabinets constitute a group of electric receivers operating in continuous mode with a constant or slightly varying load. Furnaces and drying ovens with a power of 2.5÷70 kW are classified as low and medium power consumers, powered by a voltage of 380 V, industrial frequency 50 Hz.

The machines operate for a long time, but with variable load and short-term deviations, during which the electric motor does not have time to cool down to ambient temperature, and the duration of the cycles exceeds 10 minutes. In terms of power, they are classified as low and medium power consumers, powered by a 380 V network with an industrial frequency of 50 Hz.

Fans operate in continuous mode, without shutting down, from several hours to several shifts in a row, with a fairly high, constant or slightly varying load. They belong to low and medium power consumers, powered by a 380V industrial frequency network.

Tap operates in repeated short-term mode with a shutdown duration of 40%. Power 2.2 kW, powered from a 380V network at an industrial frequency of 50 Hz.

Welding transformers operate in a repeated short-term mode with constant large surges of power, an on-time of 40%, power 48 kVA and 42 kVA, powered by a 380 V network with an industrial frequency of 50 Hz. The mechanical section belongs to the consumers of the second category.

2. Selection and justification of the power supply scheme.

Shop distribution networks must:

Ensure the necessary reliability of power supply to electricity receivers depending on their category.

Be convenient and safe to use.

Have optimal technical and economic indicators.

Have a design that ensures the use of industrial and high-speed installation methods.

Therefore, to power the workshop, a main power supply circuit is selected, which ensures a small number of connections, and therefore a reduction in the construction part; small changes in the network when the location of process equipment changes; less energy losses. Along with the advantages of the scheme, there are also disadvantages:

Lower reliability of mainline circuits compared to radial circuits.

It is more difficult to ensure selectivity of protection.

The circuit is made of distribution busbars of the ShRA type, which are designed to power low- and medium-power electrical receivers evenly distributed along the main line.

3. Calculation of electrical loads of the workshop.

Calculation of electrical loads of a workshop area is carried out using the method of ordered diagrams using the design load coefficient. The preliminary rated power of receivers with intermittent operation is reduced to PV-100% using the formulas:

P n = P pass - for electric motors (1)

Р n = S pass cosφ - for welding transformers and

Welding machines (2)

Р n = S pass cosφ - for electric furnace transformers (3)

where P pass (kW), S pass (kW), PV - passport data of power and duration of inclusion in relative units;

cosφ passport active power factor.

Welding powertransformers

kW

kW

Converter unit power

kW

Overhead Crane Power

kW

Calculation of electrical loads with voltage up to 1 kV is carried out for each power supply unit (distribution point, distribution busbar, main busbar, workshop transformer substation or for the workshop as a whole).

We accept the following values ​​for the utilization factor of electrical receivers, which is taken from.

The power unit assembly module is defined:

, (2)

Where:

Maximum rated power of the electrical receiver connected to the power supply unit, kW;

Minimum rated power of the electrical receiver connected to the power supply unit, kW.

Table 1 - Equipment utilization factors

For the power node, the value of the assembly module is determined:

where R n.max1, R n.min1  maximum and minimum power of one electrical receiver for a power supply unit.

Average values ​​of active and reactive powers for the busiest shift for groups of receivers:

(3)

, (4)

Where - utilization factor of the electrical receiver;

Sum of rated powers of electrical receivers, kW.

The average power for a power supply unit is determined by summing the active, average and reactive powers of groups of electrical receivers.

Weighted average values ​​of utilization factor and reactive power factor:

(5)

(6)

Determination of the effective number of electrical receivers n E:

For the power node the value is written n E  effective number of electrical receivers, which is determined by the formula:

If the number of power receivers is more than five, the effective number of power receivers ( n E) determined using simplified formulas depending on the assembly module and the weighted average value of the utilization factor:

a) if K u > 0.2 and m< 3, то n Э = n

b) if K u< 0.2, а m < 3, то n Э is not determined, and the design load will be:

, (8)

Where:

K z = 0.75 - for repeated short-term mode;

K z = 0.9 - for continuous mode;

K z = 1.0 - for automatic lines.

B) if, a, then:

(9)

d) if, a, then:

the effective number of electrical receivers () is determined as follows:

1) the number of electrical receivers is determined, the power of which is equal to or more than half the power of the largest receiver;

2) the total power of these electrical receivers is determined;

3) relative values ​​are determined

(10)

(11)

4) according to /4.58/ the effective relative number of electrical receivers is determined*

5) the effective number of electrical receivers is determined

(12)

, (13)

where is the design load coefficient.

The value of the design load factor is determined by /4,100/ depending on the weighted average utilization factor and the effective number of electrical receivers n E .

When n e  10 (14)

At n e  10 (15)

Total design power, kVA:

(16)

Rated current, A:

(17)

Calculation example for RP 1

1. Number of electrical receivers n=3
2. Installed power kW
3. Total rated power 118.5 kW
4. Usage rates:

carousel machine

longitudinal planer

carousel machine

1. Average power:

Longitudinal planer:

Carousel machine:

kW

1. Assembly module:

1. Average power for power supply:

kW

Kvar

1. Effective number of electrical receivers:

Since for RP1 even then

1. Weighted average utilization rate:

1. Weighted average value of reactive power factor:

1. Design load factor for and:

1. Rated current:

The calculation for other electrical receivers is carried out similarly.

The calculation results are summarized in Table 2.

4 Selection of brand and cross-section of live parts

The choice is made using the example of a cable from ShRA1 to cabinet RP1

The cross-section of wires and cables is selected according to the heating conditions for normal operating conditions:

A cable of the VVG 4×16 brand is selected, for which:

60.9 A<70А the condition is met.

(18)

where voltage loss in the conductor, V;

permissible voltage loss, V.

(19)

specific active and inductive resistance of the conductor;

l cable length (determined according to Figure 1);

0,621< 20 В - the condition is met.

If the selected cross-section does not accommodate voltage losses, then the cross-section must be increased.

The cross section is checked for compliance with the current of the protective device:

(20)

where protection factor is taken depending on the environment and

constructive implementation of current-carrying parts;

current of the protective device, the current of the fuse link or the operating current of the thermal release of the circuit breaker is taken, A.

Checking for this condition is only possible after selecting the protective equipment on the power side; an example of the calculation is given below:

The calculation of the remaining current-carrying parts is similar to the above.

The calculation results are summarized in Table 3.

5.Selection of protective and switching equipment.

For practical calculations of electrical networks with voltages up to 1000 V, the selection of protective switching equipment can be done as follows:

1. The selection of fuses is made based on the conditions:

where rated fuse voltage, V;

voltage of the installation in which the fuse is used, V.

where rated fuse current, A;

rated current, A.

where rated current of the fuse link, A;

, (21)

where is a coefficient that takes into account the increase in current when starting the engine.

with frequent and easy starts;

during heavy and rare starts;

motor starting current, A.

(22)

where is the multiplicity of the starting current

rated motor current, A.

(23)

where short-term (peak) current;

(24)

where is the largest starting current of the motors of the receiver group;

calculated current of the receiver group;

rated motor current (reduced to PV=1) with the highest starting current;

utilization factor characteristic of the motor having the highest starting current.

The choice is made using the example of a fan:

Select fuse PR2 100/100 for which:

, ;

The adopted fuse meets the above requirements.

1. Selection of circuit breakers:

Selection conditions:

where, respectively the rated current of the circuit breaker and the rated current of the release, A;

To protect connections with a uniform load:

where rated current of the thermal release of the machine;

rated current of the electromagnetic release of the machine;

For branches to motors:

; (25)

For lines with mixed load:

(26)

The choice is made using the example of a branch to the fan motor. The Sirius 3RV1031-4FB10 switch is selected, for which (look at the catalogue):

Selected switch Sirius 3RV1031-4FB10 meets the specified conditions.

The results of the selection of fuses and circuit breakers are recorded in Table 4.

6. Selection of power of workshop substation transformers.

Reactive power compensation.

The issue of choosing the power of transformers is resolved simultaneously with the issue of choosing the power of compensating devices with voltages up to 1000V:

(27)

where power of compensating devices, providing choice

optimal power of workshop transformers;

power of compensating devices selected for the purpose

minimizing power losses in workshop substation transformers and in 10 kV distribution networks.

The approximate power of transformers can be determined by the formula:

, (28)

Where :

number of transformers;

emergency transformer overload factor;

Two transformers of type TND-400/10 are accepted for which:

, (29)

Where:

addition to the nearest whole number towards the larger one;

β n load factor of transformers in normal mode;

β n =0.8 for two-transformer substations with a predominance of consumers in the workshop II category.

The minimum number of transformers of a workshop substation is determined:

(30)

Where:

additional number of transformers, determined depending on from and

The maximum possible reactive power transmitted through transformers from a 10 kV network is determined:

; (31)

Since, then it is accepted and reactive power compensation is not needed, i.e. ;

Determining additional powerBSK to reduce power losses in transformers:

, (32)

where is the calculated coefficient, determined depending on the coefficients and;

A coefficient that takes into account the location of the energy system and the shift of the enterprise;

coefficient depending on the power of the transformers and the length of the supply line.

[ 1,109]

[ 1,107]

Therefore, for a workshop substation:

The load factor of transformers in normal and post-emergency modes is determined:

The need to install the BSC is determined:

Capacitor batteries are not installed in the workshop.

Power losses in workshop transformers:

(35)

Where:

No-load losses, kW;

Short circuit losses, kW.

(36)

Where :

No-load current, %;

Short circuit voltage, %.

Active power consumed by the transformer:

Reactive power consumed by the transformer:

Total power consumed by the transformer:

(37)

7. Calculation of the 10 kV supply line.

To select a 10 kV supply line, you need to know the short circuit current on the GPP buses.

A replacement scheme is being drawn up

An equivalent circuit is drawn up, Figure 1.

Distance from the GPP to the workshop l = 0.6 km; Rice. 1 Equivalent circuit

Distance from the gas station to the power system substation L = 12 km;

Short circuit power on the 110 kV buses of the power system substation = 1500 MVA.

Transformers GPP: TMN 10000/110;

Base current:

(38)

System resistance:

O.e. (39)

Where (. ) - rated power of the system, MVA.

Air line resistance:

, (40)

where is the specific resistance of the overhead line, Ohm/km;

- length of overhead line, km.

Accepted

Transformer resistance:

, (41)

Cable line resistance:

, (42)

where is the resistivity of the cable line, Ohm/km;

l - cable line length, km.

accepted Ohm/km

l =0.6 km

Resulting resistance:

(43)

We find the steady-state value of the short circuit current:

The line cross-section is determined by the economic current density j e :

(45)

Where:

Rated current of the cable line in normal mode, A;

Economic current density, A/mm 2

We take j e =1.4 A/mm 2 [7.305]

Rated current of the cable line in normal mode:

(46)

Select 2A cable C B-10-3×16, for him

The selected section is checked:

According to heating conditions in normal mode:

The permissible cable current is determined for a long time, taking into account the laying:

number of parallel cables in a cable line.

rated current of one cable, A;

We determine the current of one cable in post-emergency mode:

(47)

where correction factor for the number of cables laid in

one trench;

correction factor for ambient temperature;

The fulfillment of the heating condition in normal mode is checked:

69 A>10.2 A the condition is met.

2. According to the heating condition in post-emergency mode:

The current of one cable in post-emergency mode is determined:

(48)

The emergency overload coefficient is determined depending on the type of cable laying, the preload coefficient and the duration of the maximum:

(49)

The permissible cable current in post-emergency mode is determined:

(50)

The fulfillment of the heating condition in the post-emergency mode is checked:

93.15 A>20.4 A the condition is met.

The selected cross section is checked based on the permissible voltage loss:

Δ U add = 0.05 10 = 0.5 kV

=, (51)

Where:

Specific active resistance of the cable, Ohm/km;

Cable specific reactance, Ohm/km;

Cable line length, km.

 the condition is met.

The cross-section is checked for thermal resistance:

, (52)

Where:

C coefficient of temperature change;

reduced short-circuit time, s;

16 < 69,1505 – это условие не выполняется.

The standard cross-section of cable cores and cable grade 2ASB-10-3×50 are finally adopted.

8. Constructive implementation of the workshop network.

Depending on the adopted power supply scheme and environmental conditions, the workshop electrical network is made of distribution busbars. Such busbar trunkings are called complete, since they are made in the form of separate sections, which consist of four busbars enclosed in a shell and held together by the shell itself.

To make straight sections of lines, straight sections are used, for turns - angular, for connections - connecting. The busbars are connected at the installation site using bolted connections. For every 3 m busbar section, up to 8 branch boxes can be installed (4 on each side). Circuit breakers or fuse switches are installed in branch boxes. The busbars are fastened with brackets to the columns at a height of 3.5 meters from the floor level.

The descent of cables and wires from the busbar to distribution cabinets or individual electrical receivers is carried out along the walls in pipes. Sections of cables feeding individual electrical receivers are laid in pipes embedded in the finished floor to a depth of 10 cm.

Cabinets with fuses or circuit breakers are used as distribution points. Cabinets with fuses have a switch at the input. Cabinets with automatic switches are made with input terminals. Technical characteristics of the cabinets are presented in Table 5.

Table 5 Distribution points

Conclusion

In the course project, a power supply diagram for a repair and mechanical workshop was developed. For this purpose, electrical loads and a 0.4 kV network were calculated, current-carrying parts and a workshop transformer were selected, and the cables supplying the workshop substation were checked for short-circuit currents.

The power supply of individual electrical receivers is carried out by cables of the AVVG brand and wires of the APV brand.

Sirius brand circuit breakers are used as protective devices.and PR-2 fuses.

This electrical network diagram can be considered rational and economical.

List of sources used

1. Fedorov A. A., Starkova L. E. Textbook for course and diploma design on power supply of industrial enterprises: Textbook. manual for universities. M.: Energoatomizdat, 1987. 368 p.: ill.
2. Handbook on the design of electrical networks and electrical equipment / edited by Barybin Yu. G. et al. M.: Energoatomizdat, 1991. 464 p., ill.
3. Handbook on power supply design / edited by Barybin Yu. G. et al. M.: Energoatomizdat, 1990. 576 p.
4. Directory of power supply for industrial enterprises /under the general title. edited by A.A. Fedorov and G.V. Serbinovsky. In 2 books. Book 1. Design and calculation information. M.: Energy, 1973. 520 p., ill.
5. Neklepaev B. N., Kryuchkov I. P. Electrical part of stations and substations. Reference materials for course and diploma design: Proc. manual for universities. 4th ed., revised. and additional M.: Energoatomizdat, 1989. 608 p., ill.
6. Electrotechnical reference book /under general. ed. Professor MPEI Gerasimov V.G. et al. 8th ed., rev. and additional M.: MPEI Publishing House, 1998. 518 p.
7. Handbook on the design of electrical power systems / edited by S.S. Rokotyan and I.M. Shapiro. 3rd ed., revised. and additional M.: Energoatomizdat, 1985. 352 p.
8. Rules for the construction of electrical installations - M.: Gosenergonadzor, 2000
9. http://electricvdome.ru/montaj-electroprivodki/raschet-secheniya-provoda kabelya.html
10. http://www.electromonter.info/library/cable_current_1.html
11. Catalog “Protection devices. Automatic switches"
12. http://www.rus-trans.com/?ukey=product&productID=1145
13. Guidelines for course design

Table 2 Calculation of electrical loads of the workshop

Continuation of table 2

The choice of power supply scheme is inextricably linked with the issue of voltage, power, category of electric power supply in terms of reliability, remoteness of electric power supply.

With regard to ensuring the reliability of power supply, power receivers are divided into the following three categories.

Electrical receivers first category– electrical receivers, the interruption of power supply to which may entail a danger to human life, a threat to state security, significant material damage, disruption of a complex technological process, disruption of the functioning of particularly important elements of public utilities, communications and television facilities.

From the first category of electrical receivers, a special group of electrical receivers is distinguished, the uninterrupted operation of which is necessary for an accident-free shutdown of production in order to prevent threats to human life, explosions and fires.

Electrical receivers second category– electrical receivers, the interruption of power supply to which leads to a massive shortage of products, massive downtime of workers, machinery and industrial transport, disruption of the normal activities of a significant number of urban and rural residents.

Electrical receivers third category– all other electrical receivers that do not fall within the definitions of the first and second categories.

Electric receivers of the first category in normal modes must be provided with electricity from two independent, mutually redundant power sources, and an interruption in their power supply in the event of a power failure from one of the power sources can be allowed only for the duration of automatic power restoration.

To supply power to a special group of electrical receivers of the first category, additional power must be provided from a third independent, mutually redundant power source.

As a third independent power source for a special group of electrical receivers and as a second independent power source for the remaining electrical receivers of the first category, local power plants, power plants of power systems (in particular, generator voltage buses), uninterruptible power supply units intended for these purposes, batteries and etc.

If power supply redundancy cannot ensure the continuity of the technological process or if power supply redundancy is not economically feasible, technological redundancy must be implemented, for example, by installing mutually redundant technological units, special devices for accident-free shutdown of the technological process, operating in the event of a power supply failure.

If feasibility studies are available, it is recommended that the power supply to power receivers of the first category with a particularly complex continuous technological process require a long time to restore normal operation from two independent mutually redundant power sources, which are subject to additional requirements determined by the features of the technological process.

Electrical receivers of the second category in normal modes must be provided with electricity from two independent, mutually redundant power sources.

For power receivers of the second category, in the event of a power supply failure from one of the power sources, interruptions in power supply are allowed for the time required to turn on the backup power by the actions of the duty personnel or the mobile operational team.

For electrical receivers of the third category, power supply can be provided from a single power source, provided that power supply interruptions necessary to repair or replace a damaged element of the power supply system do not exceed one day.

The issue of choosing a power supply scheme and voltage level is decided on the basis of a technical and economic comparison of options.

To power industrial enterprises, electrical networks with voltages of 6, 10, 20, 35, 110 and 220 kV are used.

In the supply and distribution networks of medium-sized enterprises, a voltage of 6–10 kV is accepted. Voltage 380/220 V is the main one in electrical installations up to 1000 V. The introduction of voltage 660 V is cost-effective and is recommended to be used primarily for newly built industrial facilities.

Voltage 42 V (36 and 24) is used in areas with increased danger and especially dangerous conditions, for stationary local lighting and hand-held portable lamps.

The 12V voltage is used only under particularly unfavorable conditions with regard to the risk of electric shock, for example when working in boilers or other metal containers using hand-held portable lights.

Two main electricity distribution schemes are used - radial and main, depending on the number and relative location of workshop substations or other electrical installations in relation to the point feeding them.

Both schemes provide the required reliability of power supply to ES of any category.

Radial distribution schemes are used mainly in cases where the loads are dispersed from the power center. Single-stage radial circuits are used to power large concentrated loads (pumping, compressor, converter units, electric furnaces, etc.) directly from the power center, as well as to power workshop substations. Two-stage radial circuits are used to power small workshop substations and high-voltage power receivers in order to unload the main energy centers (Fig. H.1). All switching equipment is installed at intermediate distribution points. The use of multi-stage circuits for intra-shop power supply should be avoided.

Distribution points and substations with electrical receivers of categories I and II are supplied, as a rule, by two radial lines that operate separately, each for its own section; when one of them is disconnected, the load is automatically taken up by the other section.

Rice. 3.1. Fragment of a radial power distribution diagram

Trunk power distribution circuits should be used for distributed loads, when there are many consumers and radial circuits are not economically feasible. Main advantages: they allow better loading of cables during normal operation, save the number of cabinets at the distribution point, and reduce the length of the main line. The disadvantages of mainline circuits include the complication of switching circuits, simultaneous shutdown of the electrical power supply of several production sites or workshops powered by a given mainline when it is damaged. To power power supplies of categories I and II, circuits with two or more parallel end-to-end mains should be used (Fig. 3.2).

It is recommended that electric power supply in networks with voltage up to 1000 V of categories II and III in terms of power supply reliability be carried out from single-transformer complete transformer substations (CTS).

The choice of two-transformer transformer substations must be justified. The most appropriate and economical for intra-shop power supply in networks up to 1 kV are the main circuits of transformer-main blocks without switchgear at a substation using complete busbars.

Radial circuits of intra-shop power supply networks are used when it is impossible to implement main circuits due to the conditions of the territorial location of electrical loads, as well as environmental conditions.

In design practice, radial or main circuits in their pure form are rarely used to supply power to workshop consumers. The most widespread are the so-called mixed electrical network circuits, which combine elements of both radial and main circuits.

Rice. 3.2. Scheme with double through highways

Power supply circuits and all AC and DC electrical installations of an enterprise with voltages up to 1 kV and higher must meet the general requirements for their grounding and protection of people and animals from electric shock both in normal operation of the electrical installation and in the event of insulation damage.

Electrical installations with regard to electrical safety measures are divided into:

– for electrical installations with voltages above 1 kV in networks with a solidly grounded or effectively grounded neutral;

– electrical installations with voltages above 1 kV in networks with an isolated or grounded neutral through an arc suppression reactor or resistor;

– electrical installations with voltage up to 1 kV in networks with a solidly grounded neutral;

– electrical installations with voltage up to 1 kV in networks with an insulated neutral.

For electrical installations with voltages up to 1 kV, the following designations are used. System TN– a system in which the neutral of the power source is solidly grounded, and the open conductive parts of the electrical installation are connected to the solidly grounded neutral of the source through neutral protective conductors (Fig. 3.3–3.7).

Rice. 3.3. System TN-C- system TN, in which zero protective

and neutral working conductors are combined in one conductor

along its entire length

The first letter is the state of the neutral of the power source relative to

T– grounded neutral;

I– isolated neutral.

The second letter is the state of open conductive parts relative to the ground:

T– exposed conductive parts are grounded, regardless of the relation to the ground of the neutral of the power source or any point of the supply network;

N– open conductive parts are connected to the solidly grounded neutral of the power source.

Subsequent (after N) letters - combination in one conductor or separation of the functions of the zero working and zero protective conductors:

S– zero worker ( N) and zero protective ( P.E.) conductors are separated;

C– the functions of the neutral protective and neutral working conductors are combined in one conductor ( PEN-conductor);

N– zero working (neutral) conductor;

P.E.– protective conductor (grounding conductor, neutral protective conductor, protective conductor of the potential equalization system);

PEN– combined zero protective and zero working conductor.

Zero working (neutral) conductor ( N) – a conductor in electrical installations up to 1 kV, intended for powering electrical receivers and connected to a solidly grounded neutral of a generator or transformer in three-phase current networks, with a solidly grounded output of a single-phase current source, with a solidly grounded source point in direct current networks.

Combined zero protective and zero working ( PEN) conductor - a conductor in electrical installations with voltages up to 1 kV, combining the functions of the neutral protective and neutral working conductors.

To protect against electric shock in normal operation, the following protective measures against direct contact must be applied, individually or in combination:

– basic insulation of live parts;

– fences and shells;

– installation of barriers;

– placement out of reach;

– use of ultra-low (low) voltage.

Rice. 3.4. System TN-S- system TN, in which zero protective

and zero working conductors are separated along its entire length

Rice. 3.5. System TN-C-S- system TN, in which the functions of zero

protective and neutral working conductors are combined in one

conductor in some part of it, starting from the power source

Rice. 3.6. System TT– a system in which the neutral of the power supply

solidly grounded, and open conductive parts of the electrical installation

grounded using a grounding device, electrically

source independent from the solidly grounded neutral

Rice. 3.7. System IT– a system in which the neutral of the power source

isolated from the ground or grounded through instruments or devices,

having high resistance, and exposed conductive parts

electrical installations are grounded

For additional protection from direct contact in electrical installations with voltage up to 1 kV, if there are requirements of other chapters of the PUE, it should be used residual current devices(RCD) with a rated residual current of no more than 30 mA.

To protect against electric shock in the event of insulation damage, the following protective measures for indirect contact must be applied individually or in combination:

– protective grounding;

– automatic power off;

– potential equalization;

– potential equalization;

– double or reinforced insulation;

– ultra-low (low) voltage;

– protective electrical separation of circuits;

– insulating (non-conductive) rooms, zones, areas.

Electrical installations with voltage up to 1 kV of residential, public and industrial buildings and outdoor installations should, as a rule, receive power from a source with a solidly grounded neutral using the system TN.

Power supply of electrical installations with voltage up to 1 kV AC from a source with an isolated neutral using the system IT should be performed, as a rule, if it is not permissible to interrupt the power supply during the first short circuit to ground or to exposed conductive parts connected to the potential equalization system. In such electrical installations, to protect against indirect contact during the first ground fault, protective grounding must be performed in combination with network insulation monitoring or an RCD with a rated residual current of no more than 30 mA must be used. In case of a double ground fault, the power supply must be automatically turned off in accordance with the PUE.

Power supply of electrical installations with voltage up to 1 kV from a source with a solidly grounded neutral and with grounding of exposed conductive parts using a ground electrode not connected to the neutral (system TT), is allowed only in cases where electrical safety conditions in the system T N cannot be provided. To protect against indirect contact in such electrical installations, the power must be automatically turned off with the mandatory use of an RCD.

In this case, the condition must be met

R a I a≤ 50 V,

Where I a – tripping current of the protective device;

R a is the total resistance of the grounding conductor and the grounding conductor of the most distant electrical receiver when using an RCD to protect several electrical receivers.

When using the system TN It is recommended to re-ground PE- And PEN- conductors at the entrance to electrical installations of buildings, as well as in other accessible places. For re-grounding, natural grounding should be used first. The resistance of the re-grounding electrode is not standardized.

In electrical installations with voltages above 1 kV with an insulated neutral, protective grounding of exposed conductive parts must be performed to protect against electric shock.

In adj. 3 shows power supply diagrams for individual buildings, and appendix. 4 – graphic and letter symbols in electrical circuits.