Coursework: Power supply and electrical equipment of a mechanical shop. Power supply scheme of the workshop Design of the power supply system of the machine shop drawing

FGOU SPO Cheboksary College of Construction and Municipal Economy

COURSE PROJECT

Explanatory note

1. Introduction.

2. a brief description of the designed object.

3. Development of a power supply scheme for the facility.

4. Determination of calculated power loads.

5. Calculation and selection of supply and distribution lines.

5.1 Selection of supply lines.

5.2 Selection of distribution lines.

6. Calculation of protection.

6.1 Calculation and selection of protection of supply lines.

6.2 Calculation and selection of distribution line protection.

7. Choice of location and type of power and distribution points.

8. Choice of compensating devices.

9. Selection of the number and power of transformers at the transformer substation.

10. Calculation of short circuit current.

10.1 Calculation of three-phase short circuit currents.

10.2 Calculation of single-phase short circuit currents.

11. Checking equipment for the action of short circuit currents.

12. List of references.

Introduction

At the present time it is impossible to imagine the life and work modern man without the use of electricity. The main advantage of electrical energy is the relative ease of production, transmission, crushing, and transformation.

In the power supply system of objects, three types of electrical installations can be distinguished:

for the production of electricity - power plants; for the transmission, conversion and distribution of electricity - electrical networks and substations;

on electricity consumption for industrial and domestic needs - electricity receivers.

A power plant is a plant that generates Electric Energy. At these stations different kinds energy (energy of fuel, falling water, wind, nuclear, etc.) using electrical machines, called generators, is converted into electrical energy.

Depending on the type of primary energy used, all existing stations are divided into the following main groups: thermal, hydraulic, nuclear, wind, tidal, etc.

The set of electrical receivers of production facilities of a workshop, building, enterprise, connected with the help of electrical networks to a common power supply point, called an electrical consumer.

The set of power stations, transmission lines, substations of thermal networks and receivers, united by a common continuous process of generation, transformation, distribution of thermal electrical energy, is called an energy system.

Electrical networks are divided according to the following criteria:

1) Mains voltage. Networks can be voltage up to 1 kV - low voltage, or low voltage (LV), and above 1 kV high voltage, or high voltage.

2) Type of current. Networks can be direct and alternating current.

Electric networks are carried out mainly on a three-phase alternating current system, which is the most expedient, since electricity can be transformed in this case.

3) Appointment. By the nature of consumers and the purpose of the territory in which they are located, they distinguish: networks in cities, networks industrial enterprises, electric transport networks, networks in rural areas.

In addition, there are regional networks, networks of intersystem communications, etc.

Section 1

Brief description of the designed object

The Mechanical Repair Shop (RMS) is designed to repair and adjust electromechanical devices that are out of order.

It is one of the shops steel plant smelting and processing metal. The RMC has two sections in which the equipment necessary for repair is installed: turning, planing, milling, drilling machines, etc. The workshop provides premises for a transformer substation (TP), fan, instrumental, warehouses, welding posts, administration, etc.

RMC receives ENS from the main step-down substation (MSS). The distance from the GPP to the shop TP is 0.9 km, and from the power system (ENS) to the GPP is 14 km. The voltage at the GPP is 6 and 10 kV.

The number of work shifts is 2. Shop consumers have 2nd and 3rd ENS reliability categories. The soil in the RMC area is black soil with a temperature of +20 C. Frame

the workshop building is assembled from blocks-sections 6 m long each.

Workshop dimensions

Auxiliary premises are two-story, 4 m high.

The list of RMC equipment is given in Table 1.

The power consumption is indicated for one electrical receiver.

The location of the main equipment is shown on the plan.

Table 1 List of EO of the mechanical repair shop.

Section 2

Development of a power supply scheme for an object

For the distribution of electrical energy inside the workshops of industrial enterprises, electrical networks with voltages up to 1000V are used.

The scheme of the intrashop network is determined by the technological process of production, the layout of the premises of the shop, the relative position of the electric power supply, transformer substations and power inputs, the rated power, the requirements for uninterrupted power supply, the conditions environment, technical and economic considerations.

The power supply of the EP of the shop is usually carried out from the shop substation of the transformer substation or the transformer substation of the neighboring shop.

Intrashop networks are divided into supply and distribution networks.

The supply networks depart from the central switchboard of the shop TP to the power distribution cabinets of the joint venture, to the distribution busbars of the ShRA or to individual large EPs. In some cases, the supply network is carried out according to the BTM scheme ("Block - Transformer - Main").

Distribution networks are networks that go from power distribution cabinets or busbars directly to the EA. In this case, the EA is connected to the switchgears by a separate line. It is allowed to connect up to 3-4 EPs with power up to ZkV connected in a chain by one line.

By their structure, schemes can be radial, main and mixed.

Radial schemes with the use of joint ventures 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 have high reliability and are used to power EP of any category. Networks are made with cables or insulated wires.

It is advisable to use trunk circuits to power distribution loads relatively evenly over the workshop area, as well as to power power supply groups of EP belonging to the same production line. The schemes are carried out by busbars or cables. In a normal environment, complex busbars can be used to build backbone networks.

To power the EP of the designed workshop, we use a three-phase four-pass network with a voltage of 380/220V, a frequency of 50Hz. The electrical equipment will be powered from the workshop transformer substation. Because Since consumers in terms of reliability of power supply belong to categories 2 and 3, then we install 1 transformer at the transformer substation and provide a low-voltage backup jumper from the transformer substation of the neighboring workshop.

Section 3

Determination of Design Force Loads

The correct determination of the expected (calculated) electrical loads (rated powers and currents) in all sections of the SES is the main fundamental stage of its design. The initial data for the selection of all elements of the SES depend on this calculation - the cash costs for the installation and operation of the selected equipment (EE).

An overestimation of the expected loads leads to an increase in the cost of construction, an overrun of the conductor material of networks, to an unjustified increase in the installed capacity of transformers and other electrical equipment.

Understatement - can lead to a decrease bandwidth electrical networks, overheating of wires, cables, transformers, to unnecessary power losses.

For distribution networks, the calculated power is determined by the rated power (passport) of the connected EP. In this case, the power of the EP operating in the repeated short-term mode leads to a long-term mode.

For lines supplying power supply units (power distribution points, bus ducts, workshops and enterprises in general), the calculation of the expected loads is carried out by a special method. The estimated expected power of the node is always less than the sum of the rated powers of the connected ED due to the non-simultaneity of their operation, the random probable nature of their switching on and off, therefore, the simple summation of the EP leads to a significant overestimation of the load compared to the expected one. The main method for calculating the load is the method of ordered diagrams. The method is applicable when the nominal data of all EAs and their placement on the shop plan are known.

The procedure for determining the calculated power loads by the method of ordered diagrams.

1. All EAs connected to this node are grouped according to the same technological process, but not according to the same power, while the powers of EAs operating in the intermittent mode lead to a long-term mode.

2. For each group, determine the total power, utilization factor, trigonometric functions and c. 52, table 2.11.

3. For each group, a replaceable active, reactive is determined by the formulas

Where is the average value of the active power consumed by the node.

4. For the entire node, determine , , the average value of the utilization factor for the entire node

weighted averages trigonometric functions

, .

5. For the assembly, the assembly factor is determined, where is the rated power of the most powerful EP, is the rated power of the lowest-powered EP. m can be greater than, equal to, or less than 3.

6. For a node, the effective number of power receivers is determined - this is a conditional number of EPs of the same power and operating mode that would consume the same amount of electricity per shift as real EPs. The value is determined by p. 55, 56 formulas 2.35 - 2.42.

7. According to the values and determine the coefficient of the maximum active load with. 54, table 2.13.

8. Determine the maximum calculated active power of the node:

9. Determine the maximum calculated reactive power of the node: , where is the maximum reactive power factor.

10. Determine the maximum calculated total power of the node:

11. The maximum rated node current is determined

Calculation according to the joint venture - 1.

Define the build module:

We find the active shift power of a group of identical EPs for the busiest shift:

We find the reactive shift power of a group of identical EPs for the busiest shift:

We determine the average utilization rate:

When calculating the maximum load, we select the conditions for calculating the effective number . So, for SP-1 , the effective number is not determined, and the maximum consumed active power is calculated from the load factor . kW.

Determine the maximum reactive power:

Determine the total maximum power:

We determine the maximum load current of the power point SP-1:

The calculation of loads for SP-2 - SP-7 is similar. All calculation results are summarized in Table 2.

Table 2 Summary of loads

Name of electrical receivers

Given load reduced to continuous duty

Lathes

Gear hobbing machines

Cylindrical grinding machines

Welding units

Fans

Overhead crane

Total for SP1, SP2, SP3

Sharpening machines

Lathes

Drilling machines

Lathes

Surface grinders

Total for SP4 and SP5

Planers

Milling machines

boring machines

Overhead crane

Total for SP6 and SP7

Section 4

Calculation of supply and distribution networks

According to the PUE, the cross-sections of the conductors of the power network with voltages up to 1 kV, with the number of use of the maximum load per year less than 4000, are selected by heating or by the allowable load current.

It is known that the current passing through the conductor heats it. The amount of heat released is determined by the Joule-Lenz law. The greater the current, the greater the heating temperature of the conductor. excessive heat can lead to premature wear of insulation, deterioration of contact connections, as well as a fire hazard. Therefore, the PUE establishes the maximum permissible heating temperatures for conductors, depending on the brand and material of the conductor insulation.

The current flowing through the conductor for a long time, at which the highest allowable temperature is set, is called long-term allowable heating current.

The value of currents 1 DOP for conductors of various grades and sections, taking into account the ambient temperature and laying conditions, is determined by calculation, verified experimentally and given in reference books. At the same time, the values of permissible currents are given for normal laying conditions ─ air temperature + 25 ° С, ground temperature + 15 ° С and one cable is laid in the trench.

If the laying conditions differ from normal, then the allowable current is determined with corrections for temperature and correction for the number of cables laid in one trench, then

The cross section of the conductors is selected according to the condition , where is the maximum rated current in the line in question.

4.1 Calculation and selection of supply lines

The type and brand of the network conductor is selected depending on the environment, the characteristics of the premises of its configuration, the placement of equipment, and the method of laying networks.

The supply networks will be carried out by AVVG (AVRG) cable.

The calculation results are shown in Table 3.

Table 3 Supply lines

Feed lines			Four-core cable up to 1 kV
To SP1, SP2, SP3			AVVG mm 2


			AVVG mm 2

4.2 Calculation and selection of distribution lines

Distribution lines are supposed to be made with APV brand PVC wire laid in a pipe. The wire cross section is selected according to the condition. The estimated current is determined by the formula

, where = 0.85.

We find SP1.

1) =33.3 A..

2) \u003d 41.7 A ..

3) =14.5 A..

The continuous current for any distribution line is determined from page 42 of table 2.7 for four single-core conductors.

\u003d 37 A.

Calculations for SP 2 - SP 7 are made in a similar way. The results of the calculation and selection of distribution lines are summarized in Table 4.

Table 4 Distribution lines

Line name			Wire brand
Lathes 6 … 8 Gear hobbing machines 9 … 11 Cylindrical grinders 12 … 14			AR mm 2
Welding units 3 … 5
Fans 1.2 Overhead crane 38			AR mm 2 AR mm 2
Sharpening machines 15 … 17 Lathes 20 ,21,23,24			AR mm 2
Drilling machines 18.19 Lathes 22.25 Surface grinders 26.27			AR mm 2
Planers 28 … 30 Milling machines 31.32
Milling machines 33.34 Boring machines 35 … 37 Overhead crane 39			AR mm 2

Section 5

Protection calculation

During the operation of electrical networks, violations of their normal operation are possible, in which the current in the conductors increases sharply, which causes an increase in their temperature above the value of the allowable PUE.

Such emergency modes include short circuit and overload.

In the event of a short circuit, currents can reach values ten times higher than the rated currents of electrical consumers and the permissible currents of conductors.

When electrical consumers are overloaded, increased currents flow through the windings of transformers, motors and conductors. Therefore, both power receivers and sections of networks must be protected by protection devices that turn off the section in emergency mode.

To protect electrical networks with voltage up to 1000 V, fuses, automatic switches and thermal relays of magnetic starters.

Fuses protect against short circuit currents.

Circuit breakers have either thermal, or electromagnetic, or combined (thermal and electromagnetic) releases. Thermal releases provide protection against overloads, and electromagnetic from short-circuit currents.

The choice of fuses is carried out under the following conditions:

1) for single EAs without fuses, the choice is made according to the following conditions, where is the rated current of the fuse-link, is the rated current of the line.

2) for EP with one engine

but) ;

b) ;

;

safety factor;

1.6 for difficult starting conditions;

2.5 for light starting conditions;

3) for lines supplying a group of EA with an engine

b) ;

The choice of circuit breakers is carried out according to the following conditions.

The operating current of electromagnetic or combined releases is checked by the maximum short-time current of the line

PUE, along with checking the conductors for permissible heating, establish a certain ratio between the currents of the protective device and the permissible wire currents , where - current of the protective device, K 3 - protection factor p. 46, table 2.10

5.1 Calculation and selection of protection of supply lines

The protection of the supply distribution lines will be carried out using the A3700 series switches.

Protection of the supply distribution lines is carried out by automatic switches of the A 3700 series.

The calculation and selection of power line switches is performed in the following sequence.

The peak current of the SP line is determined:

231.1 A; K I \u003d 0.6;

The cutoff current of the circuit breaker is determined:

BUT.

The limiting current is determined:

Determine the current of the protected line:

, where K Z \u003d 1, I Z \u003d 250 A.

, the condition is met.

Calculations for SP4, SP5 and SP6, SP7 are carried out similarly. The results of the calculation and selection of switches are summarized in Table 5.

Table 5 Selection of protective devices for supply lines

Line name								Protective device type

5.2 Calculation and selection of distribution line protection

Distribution lines are protected by fuses. Calculation and selection of outgoing line fuses is carried out in the following sequence;

The starting current of electrical receivers of the distribution point SP-1 is determined:

For EP 6…8:

For EP 9…11:

For EP 12…14:

The rated current of the fuse-link of electrical receivers SP-1 is determined according to the formula of Chapter 3, page 160. Table. 3.9.

For EP 6…8:

For EP 9…11:

For EP 12…14:

According to table 3.5 page 139, the normalized values of the currents of the installations are accepted.

For EP 6…8;

For EP 9…11;

For EP 12…14.

Calculations for SP2 - SP7 are carried out similarly. The calculation results are summarized in Table 6.

Table 6 Protection of distribution lines

Electrical receivers					Type of protection apparatus



EP 20,21,23,24

Section 6

The choice of location and type of power distribution points of the joint venture

Distribution networks for power supply of the workshop and power points are built using power distribution devices - these are power distribution points of the joint venture and distribution busbars. SP are used when EA is located in compact groups on the shop plan, as well as in shops with a dusty or aggressive environment. ShR are used when the location of the EP is unlikely.

The joint venture is a complete factory-made complete device for receiving and distributing electricity, controlling and protecting the electric power supply from overloads and short circuits containing knife switches, fuses, switches, meters.

ShR is a complete prefabricated bus duct assembled from separate sections and capable of taking on any configuration.

JV should place loads to save conductor material.

In the developed power supply scheme, four power distribution points are used. High-power electrical receivers must be connected directly to the low-voltage busbars of the workshop substation.

For the design of the workshop, power distribution cabinets with a knife switch at the input and fuses at the outgoing lines were adopted. As a joint venture, we use a three-phase distribution cabinet of the ShR 11 series. See page 137. table 3.3.

The technical data of the joint venture are presented in table 7

Table 7 Technical data of the joint venture

Name of joint venture	cabinet type	input device	Defense apparatus	Number of safety groups



EP 20,21,23,24

Section 7

Selection of compensating devices

Most EPs, in addition to active power, also consume reactive power. The main consumers of reactive power are IM, welding transformers, gas-discharge lamps. There must be a balance between the values of the reactive power generated by the generators of power plants and the values of the reactive power consumed by the electric power supply. Violation of this balance due to high consumption of reactive power leads to negative consequences(overcurrent of generators, increase in current load in the lines, increase in capital costs and loss of voltage in the line), therefore, an important task is to reduce the consumption of reactive power from the system (through transformers of substations of enterprises and workshops). Reactive power can be generated not only by generators of power plants, but also by other sources: overhead and cable power lines, as well as special devices called compensating devices (CU). Synchronous compensators and static capacitors are used as KU. As a KU in municipal and industrial enterprises, batteries of static capacitors are usually used.

The power of the KU is determined by the expression

actual calculated reactive power factor.

─ the most active calculated power of substations.

─ the optimal reactive power factor given by the electrical system, usually is ;

kvar.

─ reactive power, which can be transferred to the consumer by the power system in the mode of maximum active loads.

The value depends on ; = 0.03 - 0.98;

As a KU, we use a complete capacitor unit of the UK type p.90, table.8.1. with a power of 75 kvar

Table 8.1

Section 8

Selection of the number and power of transformers at the transformer substation

The number of transformers at the workshop substation is determined by the category of consumers. For power supply of EP 1 and 2 categories, two transformer substations are being built. To supply consumers of category 2, they allow the construction of a single-transformer substation in the presence of low-voltage jumpers switched on manually or automatically.

Single-transformer substations are used to supply non-responsible consumers of category 3, if the transformer is replaced or repaired within no more than 1 day.

The construction of a single-transformer substation provides significant capital cost savings.

The power of transformers is selected according to the condition:

when installing one transformer: ;

when installing two transformers: ;

where ─ the maximum rated power on the low voltage buses of the substation:

Transformers selected according to the last condition provide power to all consumers in normal mode with optimal loading of transformers of 0.6-0.7 load, and in the post-emergency mode, one transformer remaining in operation provides power to consumers, taking into account the allowable emergency overload of the transformer by 40% of SH 0 M .

=235 kVA.

As a workshop substation, we select a complete prefabricated transformer substation of the KTP series, the technical data of the KTP are given in the table table 9.11.

Choosing a transformer:

Table 9.11

Section 9

Calculation of short circuit currents

In the electrical network and electrical equipment in normal mode, the currents allowed for this installation flow.

In the event of a violation of the electrical strength of the insulation of wires or a short circuit of the equipment, an emergency short circuit occurs, causing a sharp increase in currents many times higher than the permissible currents.

Significant short-circuit currents pose a great danger to the elements of the electrical network and equipment, because excessive heating of current-carrying parts and create large mechanical forces that can lead to the destruction of electrical equipment.

Therefore, for the correct operation of electrical networks and equipment, they are selected not only under the conditions of normal operation, but also in emergency operation, so that they can withstand the effects of the highest possible short-circuit currents without damage. Determination of short-circuit currents necessary for the selection of circuit breakers for switching capacity and electrodynamic and thermal stability.

In addition, in 4-wire networks with a voltage of 380/220 V operating on deafly grounded neutrals, when shorted to a neutral wire or metal case equipment, the protective device should automatically turn off the emergency section of the network. To check the reliability of the operation of the protective device in case of short circuit, between the phase and neutral wires, it is necessary to determine the estimated current of a single-phase short circuit to earth.

9.1 Calculation of three-phase short-circuit currents

In the process of calculating a 3-phase short circuit. are defined:

one . - the initial effective value of the periodically component of the point along it determines the thermal stability and switching capacity of the device.

2 Surge value of short-circuit current - it is used to check devices, tires, insulators for electrodynamic stability.

We believe that the power of the system is many times greater than the power of the transformer, then the voltage on the LV busbars of the substations is considered unchanged. That is, we believe that the k.z. powered by a source with unlimited power.

Then the periodic component of the short circuit current remains unchanged during the entire duration of the short circuit, then we consider that I P 0 \u003d I short circuit. On the design scheme, we mark the design points of the short circuit. and for each point we draw up an equivalent circuit, on which we indicate the active and inductive components, the resistance of all elements of the circuit from the power point to the short circuit point.

Schematic diagram for calculating short-circuit currents:

Calculation of a three-phase short circuit at point K-1.

Replacement scheme:

We select the active and inductive resistance of the transformer according to Table 1.9.3. page 61: mΩ; mΩ.

We select the resistance of the winding of the release and the contacts of the machine according to, table 1.9.3. page 61: mΩ; mΩ; mΩ;A.

The resistance of the current transformer is selected according to Table 1.9.2. page 61:

mΩ; mΩ;;

where , but .

=30 mΩ.

The current of a three-phase short circuit at point K-1 is determined by the formula:

;

Calculation of a three-phase short circuit at point K-2.

Replacement scheme:

We select the resistance of the winding of the release and the contacts of the machine according to, table 1.9.3. page 61:

We determine the active and inductive resistance of the distribution lines of the supply EA:

X 0 and r 0 are determined by , table 1.9.5. page 62

We determine the total active and inductive resistances in a short-circuited circuit:

We determine the impedance in a short-circuited circuit:

\u003d 158.4 mΩ.

The current of a three-phase short circuit at point K-2 is determined by the formula:

Determine the shock value of the short circuit current:

9.2 Calculation of single-phase short-circuit currents

Single-phase short circuit current is determined to check the reliability of the operation of the protective device that is the most remote from the buses of the transformer substation and electric power supply. Calculation of single-phase short-circuit current at point K-3:

Replacement scheme:

We determine the resistance in the short-circuited loop of the phase-zero line. Resistance: single core cable

zero cable core

one strand of wire

cable loop inductive reactance

wire loop inductance

The total resistance of the phase-zero loop is determined by the formula:

Single-phase short circuit current find by the formula:

Section 10

Checking the equipment for the action of short-circuit currents

In networks up to 1000 V, the following checks of short-circuit currents are performed:

1. Automata, busbars are checked for electrodynamic stability if ≥ then the condition is met;

2. For switching capacity, i.e. for the maximum breaking current, check the machines, fuses: if ≥ then the condition is met;

3. On the reliability of the operation of the protective device in case of a single-phase short circuit to earth:

a 750 ≤ 1300,

condition is met.

Bibliography:

1. Konovalova L.L., Rozhkova L.D., "Power supply of industrial enterprises and installations" - M: Energoatomizdat, 1999

2. Lipkin B.Yu. "Power supply of enterprises and installations" - M: Higher school, 1990

3. Tsigelman I.E. "Power supply of city buildings and utilities» - M: Higher School, 1982

4. Rozhkova L.D., Kozulin V.S. "Electrical equipment of stations and substations" - M: Energoatomizdat, 1987

5. Konyukhova E.A. "Power supply of objects" - M: Energoatomizdat, 1988

6. Neklipaev B.N., Kryuchkov I.P. “Electrical part of stations and substations. Reference materials for course and diploma design. − M: Energoatomizdat, 1989

7. "Electric reference book" edited by Orlov I.N. − M: Energoatomizdat, 1989

8. "Rules for electrical installations (PUE)" - M: Knorus, 2007

9. Shekhovtsov V.P. "Calculation and design of power supply schemes". M: Forum-infa-M, 2004.

Power supply of the section of the mechanical shop No. 19

coursework

Energy

Workshop power distribution networks should: provide 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 vocational education

"Orenburg State University»

(Orsk Humanitarian and Technological Institute (branch) OSU)

Faculty of Mechanics and Technology

Department of Electricity and Electrical Engineering

COURSE PROJECT

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

Power supply of the section of the mechanical shop No. 19

Explanatory note

OGTI 140106. 65 6 4. 14. 019 PZ

Supervisor

cand. 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 power supply scheme of the workshop…………………….….…9

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

4. Selection of the brand and section of current-carrying parts (wires, cables,

busbars)…………………………………………………………………….…16

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

6. The choice of power transformers shop substation. Compensation

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

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

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

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

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

The task

Topic: Power supply of the machine shop area.

Option 19

2 transformers of the brand TMN - 10000/110 are installed at the GPP.
The distance from the GPP to the workshop is 0.6 km; from GPP to the substation of the power system 12 km.
Short-circuit power on 110 kV busbars of power grid substation Sk = 1500 MVA.

Introduction

The power supply system (SES) 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 plants, apparatus and machines for electric welding, lighting installations, etc.

Currently, the majority of consumers receive electricity from power grids.

As power 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 a power source to electrical consumers in modern industrial enterprises, electrical energy, as a rule, is transformed one or more times. Depending on the location in the power supply scheme, transformer substations are called main step-down substations or workshop transformer substations.

Workshop electricity distribution networks should:

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 (minimum reduced costs);
have a design that ensures the use of industrial and high-speed installation methods

For receiving and distributing electricity to groups of consumers

three-phase alternating current of industrial frequency with a voltage of 380 V, power distribution cabinets and points are used.

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:

choosing and applying a rational number of transformations ( best option number of transformations - two or three);
the choice and use of rational voltages (in power supply systems of industrial enterprises it gives significant savings in power losses);
the right choice location of workshop and main distribution (step-down) substations (provides minimum annual reduced costs);
further improvement of the methodology for determining electrical loads (contributes to the solution of the general problem of optimizing the construction of intra-factory 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 power losses and an increase in reliability;
a fundamentally new formulation for solving such problems as, for example, balancing (leveling) of electrical loads.

1. A 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 mode of operation, power, voltage, type of current and reliability of power supply to electrical receivers.

According to the mode of operation, power receivers can be divided into three groups:

with a long mode of operation;

with intermittent operation;

with short term operation.

Heating furnaces, drying cabinets - make up a group of electric receivers operating in a continuous mode with a constant or slightly changing load. Furnaces and drying cabinets with a power of 2.5÷70 kW belong to consumers of small and medium power, they are powered by a voltage of 380 V with an industrial frequency of 50 Hz.

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

Fans - operate in a continuous mode, without shutting down, from several hours to several shifts in a row, with a fairly high, unchanged or little changing load. They belong to consumers of low and medium power, they are powered by a 380V power frequency network.

Crane - works in a repeated short-term mode with a shutdown duration of 40%. Power 2.2 kW, powered by a 380V network of industrial frequency 50 Hz.

Welding transformers - operate in an intermittent mode with constant large power surges, duty cycle 40%, power 48 kVA and 42 kVA, powered by a 380 V mains 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 should:

Ensure the necessary reliability of power supply to power receivers, depending on their categorization.

Be comfortable 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, a main power supply scheme is selected to power the workshop, which ensures a small number of connections, and therefore a reduction in the construction part; a small change in the network when changing the location of technological equipment; less power loss. Along with the advantages of the scheme, there are also disadvantages:

Less reliability of trunk schemes compared to radial ones.

It is more difficult to ensure the selectivity of protections.

The scheme is made by distribution busbars of the ShRA type, which are designed to power low- and medium-power power consumers, evenly distributed along the line of the trunk.

3. Calculation of the electrical loads of the workshop.

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

R n \u003d R pass - for electric motors (1)

R n \u003d S pass cosφ - for welding transformers and

Welding machines (2)

R n \u003d S pass cosφ - for electric furnace transformers (3)

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

cosφ - passport active power factor.

Welding powertransformers

Converter power

Overhead Crane Power

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

We accept the following values of the coefficient of use of electrical receivers, which is taken from.

The power node assembly module is defined by:

, (2)

where:

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

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

Table 1 - Utilization factors for equipment

Name	Utilization coefficient, Ki
Hammer forging MA411, Drying cabinet, Overhead crane
Chamber electric furnace H-30, carousel, Surface grinder	0,17
conversion unit, Welding transformers
polishing machine, Planer 72.10	0,14
Chamber furnace OKB-330, Muffle furnace MP-25
Sharpening machine 3641	0,12
Fan

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 the power node.

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

(3)

, (4)

where - coefficient of use of the power receiver;

The sum of the rated powers of electrical receivers, kW.

The average power for the power node is determined by summing the active, average and reactive powers of the power receiver groups.

Average weighted values of utilization factor and reactive power factor:

(5)

(6)

Determination of the effective number of power consumers n E :

The value is written to the power node n E  effective number of power 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 ) is determined by 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 defined, and the calculated 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 power consumers () is determined as follows:

1) the number of power 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 power consumers is determined*

5) the effective number of power consumers is determined

(12)

, (13)

where is the design load factor.

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

When n e  10 (14)

When n e  10 (15)

Full rated power, kVA:

(16)

Estimated current, A:

(17)

Calculation example for RP 1

Number of electrical receivers n=3
Installed power kW
Sum of rated powers 118.5kW
Usage ratios:

carousel

planer

carousel

Average power:

Longitudinal planer:

Carousel:

Build Module:

Average power for power node:

Kvar

Effective number of electrical receivers:

Since for RP1 and then

Weighted average utilization rate:

Weighted average reactive power factor:

Design load factor for and:

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-sections of current-carrying parts

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

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

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

60.9 A<70А - the condition is met.

(18)

where - voltage losses in the conductor, V;

– allowable voltage losses, V.

(19)

- specific active and inductive resistances 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 pass through voltage losses, then the cross section must be overestimated.

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

(20)

where is the protection factor, is taken depending on the environment and

constructive performance of current-carrying parts;

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

This condition can only be checked after selection of the protective equipment on the supply side, a calculation example 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. Choice of protective and switching equipment.

For practical calculation of electrical networks with voltage up to 1000 V, the choice of protective switching equipment can be performed as follows:

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

where is the rated voltage of the fuse, V;

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

where is the rated current of the fuse, A;

- rated current, A.

where is the rated current of the fuse link, A;

, (21)

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

- with frequent and easy starts;

- with heavy and rare starts;

- starting current of the engine, A.

(22)

where is the multiplicity of the starting current

- rated motor current, A.

(23)

where is the short-term (peak) current in ;

(24)

where - the largest of the starting currents of the motors of the group of receivers;

– estimated current of the group of receivers;

– rated current of the motor (reduced to PV=1) with the largest of the starting currents;

- utilization factor characteristic of the motor with the highest starting current.

The choice is made on the example of a fan:

The fuse PR2 100/100 is selected for which:

, ;

The adopted fuse meets the above requirements.

Choice 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 mixed load lines:

(26)

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

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

The results of the selection of fuses and circuit breakers are entered in table 4.

6. The choice of power transformers shop substation.

Reactive power compensation.

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

(27)

where is the power of the compensating devices, which ensures the choice

optimal power of workshop transformers;

- the power of compensating devices, selected in order to

minimization of power losses in transformers of shop substation and in 10 kV distribution networks.

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

, (28)

where :

– number of transformers;

– emergency overload factor of transformers;

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

, (29)

where:

- addition to the nearest whole number in the direction of a larger one;

β n – load factor of transformers in normal mode;

β n \u003d 0.8 for two-transformer substations with a predominance of consumers in the workshop II category.

The minimum number of transformers of the 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 reactive power compensation is not needed, i.e. ;

Determine additional powerBSC to reduce power losses in transformers:

, (32)

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

Coefficient taking into account the location of the power 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 the 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 shop transformers:

(35)

where:

No-load losses, kW;

Short circuit losses, kW.

(36)

where :

Idle 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 supply line 10 kV.

To select a 10 kV supply line, it is necessary to know the short-circuit current on the GPP buses.

An equivalent circuit is being drawn up

An equivalent circuit is drawn up Figure 1.

Distance from GPP to shop l = 0.6 km; Rice. 1 Equivalent scheme

Distance from the GPP to the substation of the power system L = 12 km;

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

GPP transformers: TMN - 10000/110;

Basic 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;

- overhead line length, km.

accepted

Transformer resistance:

, (41)

Resistance cable line:

, (42)

where - specific resistance 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 value of the short circuit current:

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

(45)

where:

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

Economic current density, A/mm 2

We accept j e \u003d 1.4 A / mm 2 [7.305]

Estimated current of the cable line in normal mode:

(46)

2A cable is selected C B-10-3×16, for him

The selected section is checked:

According to the condition of heating in normal mode:

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

is the number of parallel cables in the cable line.

- rated current of one cable, A;

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

(47)

where is a correction factor for the number of cables laid in

one trench;

– correction factor for ambient temperature;

The heating condition is checked in normal mode:

69 A>10.2 A - the condition is met.

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

The current of one cable in the 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 allowable current of the cable in the 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 section is checked by the allowable voltage loss:

Δ U add \u003d 0.05 10 \u003d 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 is the coefficient of temperature change;

– reduced short-circuit time, s;

16 < 69,1505 это условие не выполняется.

The standard cross-section of the cable cores and the cable brand 2ASB-10-3 × 50 are finally accepted.

8. Constructive implementation of the workshop network.

Depending on the adopted power supply scheme and environmental conditions, the workshop electrical network is made with distribution busbars. Such bus ducts are called complete, since they are made in the form of separate sections, which are four tires enclosed in a sheath and fastened by the sheath itself.

Straight sections are used to make straight sections of lines, corner sections are used for turns, and connecting sections are used for connections. The connection of tires at the installation site is made by bolted connections. Up to 8 branch boxes (4 on each side) can be installed for every 3 m busbar section. In junction boxes, automatic switches or fuse switches are installed. The busbars are fastened with brackets to the columns at a height of 3.5 meters from the floor level.

The descent of cables, wires from the busbar to distribution cabinets or individual electrical receivers is carried out along the walls in pipes. Sections of cables supplying 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 knife switch at the input. Cabinets with automatic switches are made with clamps at the input. Specifications cabinets are presented in table 5.

Table 5 - Distribution points

RP	cabinet type	Nom. cabinet current I nsh , A	Number of outgoing lines	Nom. fuse current I n , A	Fuse type	Type of circuit breaker
RP1	PR8501-011					Sirius 3RV10-42-4JA10
RP2	PR8501-011					Sirius 3RV10-42-4JA10
RP3	PR8501-007					Sirius 3RV10-42-4JA10
WP4	ShR11-73703 R18-353				PR-2	Sirius 3VL27-16-1AS33
WP5	ShR11-73703 R18-353					Sirius 3VL27-16-1AS33
RP6	PR8501-017					Sirius 3RV10-42-4JA10
WP7	PR8501-011				PR-2	Sirius 3VL27 16-1AS33

Conclusion

In the course project, a power supply scheme for the repair and mechanical shop 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 tested 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 fuses brand PR-2.

This scheme of the electrical network can be considered rational and economical.

List of sources used

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

Table 2 - Calculation of the electrical loads of the workshop

Continuation of table 2

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At the first stage, a project is being developed for the distribution intra-shop network (RVS), which must comply with the recommendations of the PUE, SNiP, PTE, PTB. On the basis of the RVS, a design scheme for the power supply of the workshop is drawn up.

RVS is developed according to the already known construction drawing of the shop, with the specified arrangement of equipment and the known electric power of individual receivers. The drawing indicates the installation locations of the SU and RP, the network is traced. Distribution networks can be implemented using distribution busbars.

According to their structure, the schemes of intrashop electrical networks are radial, main and mixed.

Radial schemes (Fig. 4.1 a) are used in the presence of groups of concentrated loads with an uneven distribution of them over the area of \u200b\u200bthe workshop, in explosion and fire hazardous workshops, in workshops with a chemically active or aggressive environment. Radial circuits are used in pumping and compressor stations, at petrochemical enterprises, in foundries and other shops. Radial circuits of intrashop networks are performed with cables or insulated wires. They can be applied to loads of any reliability category.

The advantage of radial circuits is their high reliability. The disadvantages are: low efficiency associated with a significant consumption of conductor material, pipes, switch cabinets; a large number of protective and switching equipment; limited flexibility of the network during PE movements caused by changes in the technological process; low degree of industrialization of installation.

It is advisable to use trunk circuits to supply power and lighting loads distributed relatively evenly over the workshop area, as well as to supply a group of PEs belonging to the same production line. With trunk schemes, one supply line serves several distribution cabinets and large PE workshops.

The advantages of trunk schemes are: simplification of transformer substations; high flexibility of the network, which makes it possible to rearrange technological equipment without changing the network; the use of unified elements (bus ducts) that allow installation by industrial methods. The disadvantage is lower reliability compared to radial circuits, since in the event of an accident on the main line, all PEs connected to it lose power.

In practice, radial or trunk schemes are rarely found in their pure form. The most common are mixed (combined) circuits (Fig. 4.1 b), combining elements of radial and main circuits and suitable for any category of power supply. Such schemes are widely used in industry. In mixed circuits, from the main supply lines and their branches, electrical receivers are fed through busbars, depending on the location of the equipment in the workshop.

In areas with low load, where the laying of distribution busbars is not advisable, distribution stations are installed, connected to the nearest busbars (distribution or main).

In workshops with a predominance of loads of the 1st and 2nd categories, backup jumpers between adjacent substations should be provided.

The choice of the type of intrashop electrical network scheme is determined by many factors:

placement of equipment and power of electrical equipment installed on it;

fire and explosion hazard of production;

microclimatic conditions and characteristics of the environment in the locations of electrical equipment.

Taking into account the main provisions of the foregoing, having familiarized yourself with the characteristics of the premises, technological equipment, electrical receivers, choosing the type of electrical network, power supply source, its location and characteristics, it is necessary to take into account the following recommendations that will allow you to draw up the initial version of the design scheme:

one feeder can supply power to one or more RP connected according to the main power supply circuit;

feeder current should not exceed 300-400 A;

the electrical load on each RP should not exceed 200-250 A;

to connect an electrical receiver with a power of more than 20 kW, a separate power supply line should be allocated;

electrical receivers with a power of less than 10 kW (especially for the same type of equipment) it is rational to turn on<цепочкой>, that is, connect them in series to one line, but their number should be chosen so that the total load power does not exceed 20 kW;

RP are made of floor, hinged and recessed execution, one-sided or two-sided service. The method of their installation depends on this (near the building column, against the wall or recessed into the wall) and, as a result, the location in the workshop and on the plan of the power supply network;

Single-sided maintenance switchgear can be installed with the rear wall close to the wall;

RP two-way service must be accessible from the front and rear side;

input of wires into the floor-mounted distribution switchgear, having the form of cabinets, is carried out in pipes in the lower part of the cabinet;

RP are installed near the location of electricity receivers with an average radius of lines extending from the RP of 10-30 m;

The RP should provide branch redundancy, that is, you should choose a RP that has 1–2 more groups at the output than is required to connect the receivers for this project.

FGOU SPO Cheboksary College of Construction and Municipal Economy

COURSE PROJECT

Explanatory note

Introduction.

Brief description of the object being designed.

Development of a power supply scheme for the facility.

Determination of calculated power loads.

Calculation and selection of supply and distribution lines.

5.1 Selection of supply lines.

5.2 Selection of distribution lines.

Protection calculation.

6.1 Calculation and selection of protection of supply lines.

6.2 Calculation and selection of distribution line protection.

Choice of location and type of power and distribution points.

The choice of compensating devices.

The choice of the number and power of transformers at the transformer substation.

Short circuit current calculation.

10.1 Calculation of three-phase short circuit currents.

10.2 Calculation of single-phase short circuit currents.

Checking equipment for the action of short-circuit currents.

Bibliography.

Introduction

At present, it is impossible to imagine the life and activities of modern man without the use of electricity. The main advantage of electrical energy is the relative ease of production, transmission, crushing, and transformation.

In the power supply system of objects, three types of electrical installations can be distinguished:

for the production of electricity - power plants; for the transmission, conversion and distribution of electricity - electrical networks and substations;

on electricity consumption for industrial and domestic needs - electricity receivers.

A power plant is a plant that generates electricity. At these stations, various types of energy (energy of fuel, falling water, wind, nuclear, etc.) are converted into electrical energy using electrical machines called generators.

Depending on the type of primary energy used, all existing stations are divided into the following main groups: thermal, hydraulic, nuclear, wind, tidal, etc.

The set of electrical receivers of the production facilities of a workshop, building, enterprise, connected via electrical networks to a common power supply point, is called an electrical consumer.

Electrical networks are divided according to the following criteria:

1) Mains voltage. Networks can be voltage up to 1 kV - low voltage, or low voltage (LV), and above 1 kV high voltage, or high voltage.

2) Type of current. Networks can be direct and alternating current.

Electric networks are carried out mainly on a three-phase alternating current system, which is the most expedient, since electricity can be transformed in this case.

3) Appointment. According to the nature of consumers and the purpose of the territory in which they are located, they are distinguished: networks in cities, networks of industrial enterprises, networks of electric transport, networks in rural areas.

In addition, there are regional networks, networks of intersystem communications, etc.

Section 1

Brief description of the designed object

The Mechanical Repair Shop (RMS) is designed to repair and adjust electromechanical devices that are out of order.

It is one of the workshops of a metallurgical plant that smelts and processes metal. The RMC has two sections in which the equipment necessary for repair is installed: turning, planing, milling, drilling machines, etc. The workshop provides premises for a transformer substation (TP), fan, instrumental, warehouses, welding posts, administration, etc.

The number of work shifts is 2. Shop consumers have 2nd and 3rd ENS reliability categories. The soil in the RMC area is black soil with a temperature of +20 C. Frame

the workshop building is assembled from blocks-sections 6 m long each.

Workshop dimensions

Auxiliary premises are two-story, 4 m high.

The list of RMC equipment is given in Table 1.

The power consumption is indicated for one electrical receiver.

The location of the main equipment is shown on the plan.

Table 1 List of EO of the mechanical repair shop.

No. on the plan	EO name
	Fans
	Welding units
	Lathes
	Gear hobbing machines
	Grinding machines
	Sharpening machines
	Drilling machines
	Lathes
	Surface grinders
	Planers
	Milling machines
	boring machines
	Overhead cranes

Section 2

Development of a power supply scheme for an object

For the distribution of electrical energy inside the workshops of industrial enterprises, electrical networks with voltages up to 1000V are used.

The scheme of the intrashop network is determined by the technological process of production, the layout of the premises of the workshop, the relative position of the electric power supply, transformer substations and power inputs, the rated power, the requirements for uninterrupted power supply, environmental conditions, and technical and economic considerations.

The power supply of the EP of the shop is usually carried out from the shop substation of the transformer substation or the transformer substation of the neighboring shop.

Intrashop networks are divided into supply and distribution networks.

By their structure, schemes can be radial, main and mixed.

The scheme of the workshop power network up to 1000 V is determined by the technological process of production, the mutual arrangement of workshop TS or power input and electrical receivers, their unit installed power and placement over the area of the workshop. The scheme must be simple, safe and convenient to operate, economical, meet the characteristics of the environment, ensure the use of industrial installation methods.

The lines of the workshop network, extending from the workshop TP or input device, form a supply network, and those supplying energy from busbars or RP directly to power receivers form a distribution network.

Network schemes can be radial, trunk and mixed - with one-way or two-way power supply.

Radial power supply scheme of the workshop network

With a radial scheme, energy from a separate power supply unit (TP, RP) is supplied to one sufficiently powerful consumer or to a group of power receivers. Radial schemes are performed as single-stage, when the receivers are powered directly from the transformer substation, and as two-stage, when they are connected to an intermediate RP.

Rice. 1. Radial power supply scheme: 1 - TP switchboard, 2 - power RP, 3 - power receiver, 4 - lighting board

Radial circuits are used to power concentrated loads of high power, with uneven placement of receivers in the workshop or in groups in its individual sections, as well as to power receivers in explosive, fire and dusty rooms. In the latter case, the control and protection equipment for electrical receivers installed on the switchgear is taken out of the unfavorable environment.

Radial circuits are performed with cables or wires in pipes or boxes (trays). The advantages of radial circuits are high reliability (an accident on one line does not affect the operation of receivers powered by another line) and ease of automation. Increasing the reliability of radial circuits is achieved by connecting the buses of individual TS or RP with redundant jumpers, on the switching devices of which (automatic machines or contactors) an ATS circuit can be performed - automatic backup power input.

The disadvantages of radial circuits are: low efficiency due to the significant consumption of conductor material, the need for additional space to accommodate power RP. Limited flexibility of the network when moving technological mechanisms associated with a change in the technological process.

The main power supply circuit of the workshop network

With trunk circuits, receivers are connected to any point on the line (trunk). The mains can be connected to the switchboards of the substation or to power distributors, or directly to the transformer according to the transformer-line block diagram.

Trunk circuits with are used when supplying receivers of one production line or with receivers evenly distributed over the workshop area. Such schemes are carried out using busbars, cables and wires.

Rice. Fig. 2. Main circuits with unilateral power supply: a - with distribution busbars, b - transformer-main block, c - chain, 1 - switchboard of the transformer substation, 2 - power distribution switchgear, 3 - power receiver, 4 - main busbar, 5 - distribution busbar

When installing low-power electrical receivers at the workplaces of a technological line, it is advisable to carry out distribution lines with modular wiring. For the backbone of the modular network, insulated wires are used, laid in pipes hidden in the floor, with the installation of junction boxes at a certain distance from each other (module), on which floor distribution columns are mounted with plug connectors. Electrical receivers are connected to the speakers with wires in metal hoses. Modular wiring is used for line loads up to 150 A,

The advantages of trunk circuits are: simplification of substation shields, high network flexibility, which makes it possible to move technological equipment without altering the network, the use of unified elements that allow installation by industrial methods. The main circuit is less reliable than the radial one, since when the voltage on the main line fails, all consumers connected to it lose power. The use of busbars and modular wiring of a constant cross section leads to some overspending of the conductor material.

Mixed power scheme

Depending on the nature of production, the location of electrical receivers and environmental conditions, power networks can be carried out according to a mixed scheme. Some of the electrical receivers are powered from the mains, some - from the power distributors, which, in turn, are powered either from the switchboard of the transformer substation, or from the main or distribution busbars.

Modular wiring can be powered from distribution busbars or from power distributors connected in a radial pattern. This combination allows you to more fully use the advantages of radial and main circuits.

Rice. 3. Two-way power supply schemes: a - main with a distribution busbar, b - radial with a reserving jumper, c - with mutual redundancy of mains

To improve the reliability of power supply to power receivers according to the main circuits, a two-way supply of the main line is used. When laying several mains in large workshops, it is advisable to feed them from separate transformer substations by making jumpers between the mains. Such main power supply schemes with mutual redundancy increase power supply reliability, create convenience for repair work at substations, provide the ability to turn off unloaded transformers, as a result of which power losses are reduced.

Option 19

1. A brief description of the electrical receivers of the workshop.

2. Selection and justification of the power supply scheme.

3. Calculation of the electrical loads of the workshop.

Table 5 - Distribution points

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