Power supply diagram of a site or workshop. Power supply design for the mechanical assembly shop. All places in a given workshop have local lighting

The scheme of a shop power network up to 1000 V is determined by the technological process of production, the mutual arrangement of shop TP or power input and electrical receivers, their unit installed capacity and placement over the shop floor. The circuit should be simple, safe and easy to use, economical, meet the characteristics of the environment, and ensure the use of industrial installation methods.

The lines of the shop network, departing from the shop TP or the input device, form a supply network, and those supplying energy from bus ducts or RP directly to power consumers form a distribution network.

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

Radial power supply circuit 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 electrical consumers. Radial circuits are performed in single-stage, when the receivers are powered directly from the transformer, and in two-stage, when they are connected to the intermediate RP.


Fig. 1. Radial power circuit: 1 - switchboard TP, 2 - power RP, 3 - power receiver, 4 - lighting board

Radial circuits are used to supply concentrated loads of high power, with uneven placement of receivers in a shop or in groups in its individual sections, as well as for powering receivers in explosive, fire hazardous and dusty rooms. In the latter case, the equipment for control and protection of electrical receivers installed on the RP is removed outside the adverse environment.

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

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

Main power supply circuit of the shop network

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

Trunk circuits with are used when feeding the receivers of one technological line or with receivers evenly distributed over the area of \u200b\u200bthe workshop. Such schemes are performed using busbars, cables and wires.

Fig. 2. Trunk circuits with one-way power supply: a - with distribution bus ducts, b - transformer-main unit, c - chain, 1 - TP switchboard, 2 - power RP, 3 - electrical receiver, 4 - main bus duct, 5 - distribution bus duct

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

The advantages of trunk circuits are: simplification of substation panels, high flexibility of the network, which makes it possible to move technological equipment without reworking the network, the use of unified elements that allow installation by industrial methods. The trunk circuit is less reliable than the radial one, since when the voltage on the trunk 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 conductive material.

Mixed power scheme

Depending on the nature of production, the location of electrical receivers and environmental conditions, power networks can be performed according to a mixed scheme. Some of the electrical receivers receive power from the mains, some - from the power transformer substations, which, in turn, are powered either from the transformer substation board, or from trunk or distribution bus ducts.

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

Fig. 3. Bilateral power supply circuits: a - trunk with a distribution busbar, b - radial with a redundant jumper, c - with mutual redundancy of highways

In order to increase the reliability of power supply of electrical receivers according to trunk circuits, two-way power supply of the trunk line is used. When laying several highways in large workshops, it is advisable to feed them from separate transformer substations by making jumpers between the highways. Such backbone power supply circuits with mutual redundancy increase power reliability, create convenience for repair work at substations, and provide the ability to disconnect unloaded transformers, as a result of which power losses are reduced.

The choice of a 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 consumers are divided into the following three categories.

Electrical receivers of the first category are electrical receivers, the interruption of power supply of which may entail: danger to human life, threat to state security, significant material damage, disruption of a complex technological process, disruption of the functioning of especially important elements of communal services, communication and television facilities.

A special group of electrical receivers is distinguished from the composition of power consumers of the first category, the uninterrupted operation of which is necessary for a trouble-free shutdown of production in order to prevent threats to human life, explosions and fires.

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

Consumers of the third category - all other electrical consumers that do not fall under 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 a break in their power supply in the event of a power failure from one of the power sources can be allowed only for the time of automatic power restoration.

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

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

If the power supply backup cannot ensure the continuity of the technological process or if the power supply backup is economically inexpedient, technological backup should be carried out, 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 failure.

Power supply to power consumers of the first category with a particularly complex continuous technological process that requires a long time to restore normal operation, in the presence of feasibility studies, is recommended to be carried out from two independent mutually redundant power sources, to which additional requirements are imposed, determined by the specifics of the technological process.

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

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

For electrical receivers of the third category, power supply can be performed from one power source, provided that the power supply interruptions required for repair or replacement of a damaged element of the power supply system do not exceed 1 day.

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

For power supply, industrial enterprises use power grids with a voltage of 6, 10, 35, 110 and 220 kV.

In the supply and distribution networks of medium-sized enterprises, the voltage is 6–10 kV. Voltage 380/220 V is the main one in electrical installations up to I000 V. The introduction of 660 V is cost-effective and is recommended primarily for newly built industrial facilities.

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

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

There are two main schemes of electric power distribution - radial and main, depending on the number and relative position of shop substations or other electronic devices in relation to the point supplying them.

Both schemes provide the required reliability of power supply for an EDS of any category.

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

Fig. 3.1. Fragment of a radial power distribution diagram

Distribution points and substations with power consumers of categories I and II are fed, as a rule, through two radial lines, which work separately, each to its own section, when one of them is disconnected, the load is automatically taken over by the other section.

Trunk distribution schemes of electricity should be used with distributed loads, when there are many consumers and radial schemes are economically impractical. The main advantages: allow better loading of cables during normal operation, save the number of cabinets at the distribution point, reduce the length of the trunk. The disadvantages of trunk circuits include: the complication of switching circuits, the simultaneous shutdown of the electric power of several production sites or workshops that are powered by this trunk when it is damaged. To supply power supply of I and II categories, circuits with two or more parallel through lines should be used (Fig. 3.2).

Fig. 3.2. Dual loop through circuit

It is recommended to supply electric power in networks with voltages up to 1000 V of II and III categories in terms of power supply reliability from single-transformer complete transformer substations (KTP).

The choice of two-transformer KTP should be justified. The most expedient and economical for intrashop power supply in networks up to 1 kV are the main circuits of the transformer-main units without switchgear at the substation using complete busbars.

Radial circuits of intrashop supply networks are used when it is impossible to execute trunk circuits due to the conditions of territorial distribution of electrical loads, as well as environmental conditions.

For power supply of shop consumers in design practice, radial or trunk circuits are rarely used in their pure form. The most widespread are the so-called mixed circuits of electrical networks, combining elements of both radial and trunk circuits.

Power supply circuits and all AC and DC electrical installations of an enterprise with a voltage of up to 1 kV and above 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 case of insulation damage.

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

- electrical installations with voltages above 1 kV in networks with solidly grounded or effectively grounded neutral;

- electrical installations with a voltage higher than 1 kV in networks with an insulated 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 isolated neutral.

For electrical installations with voltage up to 1 kV, the following designations are adopted: system TN - a system in which the neutral of the power supply is grounded, and the exposed conductive parts of the electrical installation are connected to the grounded neutral of the source by means of zero protective conductors (see Fig. 3.3-3.7).

Fig. 3.3. System TN-C - system TNin which the zero protective

and neutral working conductors are combined in one conductor

throughout its entire length

The first letter is the state of the power supply neutral to ground:

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 relationship to the ground of the neutral of the power supply or any point of the supply network;

N - exposed conductive parts are connected to the dead-grounded neutral of the power supply.

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

S - zero worker ( N) and zero protective ( PE) the conductors are separated;

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

N - zero working (neutral) conductor;

PE - protective conductor (grounding conductor, neutral protective conductor, protective conductor of the equipotential bonding system);

PEN - combined zero protective and zero working conductor.

Fig. 3.4. System TN-S - system TNin which the zero protective

and zero working conductors are separated along its entire length

Fig. 3.5. System TN-C-S - system TNin which functions of zero

protective and neutral working conductors are combined in one

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

Fig. 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 by a grounding device, electrically

independent of a solidly grounded neutral source

Fig. 3.7. System IT- a system in which the neutral of the power supply

isolated from earth or grounded through appliances or devices,

high resistance, and exposed conductive parts

electrical installations are grounded

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

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

For protection against electric shock during 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;

- the use of ultra-low (low) voltage.

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

To protect against electric shock in the event of insulation damage, the following protective measures against 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, platforms.

Electrical installations with voltages up to 1 kV in residential, public and industrial buildings and outdoor installations should, as a rule, be powered from a source with a solidly grounded neutral using a 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, when it is inadmissible to interrupt the power supply at the first earth fault or to open conductive parts associated with the potential equalization system. In such electrical installations, for protection against indirect contact during the first earth fault, protective grounding must be performed in combination with network insulation monitoring or an RCD with a rated residual current of not more than 30 mA must be used. In case of a double earth fault, an automatic power off must be performed 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 an earthing switch not connected to the neutral (system TT), is allowed only in cases where the electrical safety conditions in the system T N cannot be provided. For protection against indirect contact in such electrical installations, an automatic power off must be performed with the mandatory use of an RCD.

In this case, the following condition must be met:

R a I a ≤ 50 B,

where I a - tripping current of the protective device;

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

When applying the system TN re-grounding is recommended PE- and PEN-conductors at the entrance to electrical installations of buildings, as well as in other accessible places. For re-grounding, first of all, natural grounding conductors should be used. Re-grounding resistance 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 the power supply diagrams of individual buildings, and in app. 4 - graphic and letter symbols in electrical circuits.

INTRODUCTION

The increase in the level of electrification of production and the efficiency of energy use is based on the further development of the energy base, the continuous increase in electrical energy. Currently, in the presence of powerful power plants, combined into electrical systems with high reliability of power supply, the construction of power plants continues at many industrial enterprises. The need for their construction is determined by the great distance from power systems, the need for thermal energy for industrial needs and heating, the need for backup power supply to responsible consumers. The design of power supply systems is carried out in a number of design organizations. As a result of generalization of the design experience, the issues of power supply of enterprises received the form of standard solutions. Currently, methods have been developed for calculating and designing shop networks, choosing the capacity of shop transformers, a method for determining shop loads, etc. In this regard, the issues of training highly qualified personnel who can successfully solve problems of designing power supply and practical problems are of great importance.

In this course project, a diagram of a transformer substation and a description of its operation will be considered. The calculation of the choice of the most optimal transformer will also be made.

The purpose of the course project is: selection and justification of the power supply scheme and installed electrical equipment for the designed facility.

Research object: mechanical repair shop

Subject of research: stages of calculation and selection of a power supply system for a mechanical repair shop.

Hypothesis: when developing an electrical diagram of a mechanical repair shop, an optimal option was found that ensures reliable uninterrupted operation of electrical equipment, taking into account the safety of its maintenance.

To achieve this goal and test the hypothesis, the following tasks were set:

Select the number and power of the supply substation transformers;

Design a single-line power supply diagram for a production workshop.

1. MAIN PART

1 Object characteristics

The production workshop is engaged in the manufacture of various parts and metal structures required for the main production. The workshop includes various metalworking machines, welding and lifting equipment, and fans. The power of the shop's electrical receivers ranges from 5 to 30 kW. Electric receivers operate in long-term (metal-working machines, fans) and repeatedly short-term (lifting equipment). The shop's electrical receivers operate on an alternating 3-phase current (metalworking machines, fans, lifting equipment) and a single-phase current (lighting). The shop's electrical receivers belong to the third category in terms of the required degree of power supply reliability. The environment in the workshop is normal, therefore all equipment in the workshop is of normal design. The workshop area is 367m 2

Characteristics of electrical equipment in table. 1.1

Table 1 . 1

According to plan

Name of electrical receivers

R nom, kW

Lathe

Lathe

Lathe

Lathe

Lathe

Lathe

Carousel machine with CNC

Milling machine

Milling machine

Milling machine

Milling machine

Fan

Fan

Crane - beam PV \u003d 40%

Crane - beam PV \u003d 40%

Fan

Fan

Figure 1.1 shows the plan of the projected workshop

Figure 1.1 Plan of the projected workshop

1.2 Description of the power supply diagram

The power supply of the production department is carried out from a single-transformer substation 6 / 0.4 kV with a transformer capacity of 160 kVA. In turn, the 6 / 0.4 kV transformer substation is powered by an AAB 3x10 cable line laid in the ground from an upstream two 110/6 kV transformer substation with 2500 kVA transformers each, which is powered from the power system via a single-circuit overhead line A-70.

On the 6kV side of the 6 / 0.4 transformer substation, oil switches and disconnectors are installed as protective switching equipment.

Fuses are installed on the 0.4 kV side as short-circuit protection devices

3 Power and lighting network design

For the reception and distribution of electricity in the production workshop, switchboards are installed.

Electric receivers are powered from the ШР by a wire laid in the pipes

Fuses are used as protection devices against short-circuit currents

The workshop was illuminated by 28 RKU luminaires with high-pressure mercury lamps 400W

Lighting networks are performed with APV-2.5mm² wire laid in the pipe

The working lighting is powered from the OShchV-12 lighting panel, in which automatic switches are installed as protection devices against short-circuit and overload currents

2. CALCULATION PART

1 Lighting calculation

Lighting is calculated using the luminous flux utilization method. We will show the calculation using the example of section I. As a light source, we will use a 400 W DRL lamp for the installation.

The number of light sources is determined by the formula:

where E norm is the normalized illumination, E norm \u003d 300 lux is the coefficient taking into account the decrease in luminous flux during operation, Z \u003d 1.1

K z - coefficient taking into account the uneven distribution of the luminous flux on the illuminated surface, K z \u003d 1.5 - area of \u200b\u200bthe room, m2

Ф l - luminous flux of one lamp, Ф l \u003d 22,000 lm, - the utilization factor of the luminous flux is determined depending on the type of luminaire, lamp, reflection coefficients and room index i

We find the room index by the formula:

where i is the room indicator

A - room length, m

В - room width, m

H p - the height of the lamp suspension above the working surface, m

For RKU luminaire at ρ n \u003d 50%; ρ c \u003d 30%; ρ p \u003d 10% and i \u003d 1.34 u \u003d 0.48

where ρ n - coefficient of reflection from the ceiling,%

ρ c - coefficient of reflection from walls,%

ρ p - coefficient of reflection from the working surface,%

we determine by the formula (1) the number of lamps: \u003d

Find the number of emergency lighting fixtures (25% of the working one):

We install 8 lamps in 2 rows of 4 pieces in a row

For the rest of the sections, the calculation is similar, the results are summarized in table. 2.1.

Table 2.1

Name plot

Lamp type

Land area, m2

2 Calculation of electrical loads

The calculation is carried out for the load node by the method of ordered diagrams according to the following algorithm

a) All receivers of a given load node are divided into characteristic technological groups

b) For each group, find the utilization factor Ki, the active power factor cosφ and reactive according to the formula:

(2.3)

c) We find the installed power for each group of electrical consumers using the formula:

P mouth \u003d N (2.4)

where N is the number of receivers nom - the rated power of the receivers, kW

d) For each technological group, find the average shift active P cm and average shift reactive power Q cm according to the formulas:

P cm \u003d K and P st (2.5) cm \u003d P cm tanφ (2.6)

e) For a given load node, the total installed power, the total average shift active power and the total average shift reactive power are found: ΣР mouth; ΣР cm; ΣQ cm

f) Determine the group utilization rate by the formula:

K i.gr \u003d ΣP cm / ΣQ cm (2.7)

where ΣР cm - total shift average active power, kW;

ΣQ cm - total shift average reactive power, kVar

g) Determine the load modulus by the formula:

where Р nom.max - active rated power of the largest receiver in the group, kW

Р nom.min - active rated power of the smallest receiver in the group, kW

h) Determine the effective number of receivers according to the condition:

if m ≤ 3, n ≥ 4, then n e \u003d n; for m\u003e 3, K i.gr< 0,2, эффективное число приёмников определяют в следующем порядке:

) the largest power consumer of the considered node is selected

) electrical consumers are selected, the power of each of which is equal to or more than half of the largest power consumer

) calculate their number n ′ and their total rated power P ′ nom

) determine the total rated power of all working electrical receivers of the considered node Р nom∑ and their number n

) find n ′ * and P ′ nom *:

′ * \u003d N ′ / n (2.9)

P 'nom * \u003d P' nom / R nom∑ (2.10)

) by n ′ * and P ′ nom * determine n ′ e * according to the schedule

) find n e:

n e \u003d n ′ e * n (2.11)

i) Determine, depending on the group utilization factor and the effective number of electrical receivers, the maximum coefficient K m by graphic dependencies or

j) Determine the calculated active power by the formula:

P m \u003d K m ΣP cm (2.12)

k) Determine the calculated reactive power by the formula:

if n e ≤ 10, then Q m \u003d L m ΣQ cm (2.13)

if n e\u003e 10, then Q m \u003d ΣQ cm (2.14)

where L m is the coefficient of maximum reactive power, L m \u003d 1.1

m) Determine the total design load S m by the formula:

m) Determine the rated current I by the formula:

where U is the rated voltage of power consumers, kV

The active design lighting load is determined by the formula:

R p.o \u003d K s P mouth (2.17)

where K c is the demand coefficient, K c \u003d 0.8

by formula (2.4):

P mouth \u003d 28 0.4 \u003d 11.2 kW

R p.o \u003d 0.8 11.2 \u003d 8.96 kW

By formula (2.3) we find: tgφ \u003d 0.62

using the formula (2.6), we find the calculated reactive lighting load:

Q p.o \u003d 8.96 0.62 \u003d 5.6 kvar

The full load on the 0.38 kV TP busbars is determined by the formula:

р \u003d √ (P м∑ + Р р.о) ² + (Q м∑ + Q р.о) ² (2.18)

where P m∑ is the total power load on the 0.38 kV transformer substation buses, kW m∑ is the total reactive load on the 0.38 kV transformer substation buses, kvar

The calculation results for all load nodes are summarized in table. 2.2

Table 2.2

Naim. knot gr. EP

R set kW

R nom kW

Cosφ tgφ

1) milling machines






2) lathe






3) carousel machine. CNC

0,5 1,73






4) crane-beam PV \u003d 40%

0,5 1,73






On tires ШР-1


1) milling machines

0,4 2,35






2) Fans

0,8 1,73






On tires ШР-2


1) lathes

0,4 2,35






2) Fans

0,8 1,73






3) crane-beam PV \u003d 40%

0,5 1,73






On ShR-3 tires


Lighting











On tires 0.38 TP












2.3 Reactive power compensation

The power of the compensating device is calculated by the formula:

ku \u003d α ΣР calc (tgφ avg -tgφ s) (2.19)

where α is a coefficient that takes into account the possibility of reactive power compensation by natural methods, α \u003d 0.9

ΣР calculated - total calculated active load, kW

tgφ с - factor of reactive power, which must be achieved after compensation of reactive power, according to the assignment: tgφ с \u003d 0.45.

tgφ avg is the weighted average value of the reactive power factor, calculated by the formula:

(2.20)

where ΣQ calc is the total calculated reactive load

The total design load on the 0.38 kV busbars of the transformer substation, taking into account the reactive power compensation, is calculated by the formula:

4 Selection of the number and power of the supply substation transformers

Since the electrical receivers of the production department belong to consumers of the 3rd category according to the required degree of reliability of power supply, then 1 transformer can be installed at the substation

In accordance with the load, we outline 2 options for the power of transformers:

var - 1 X 160 kVA

var - 2 X 63 kVA

Let's show the calculation using the example of option 2

We check the transformers for normal operation. Find

load factor of transformers:

(2.22)

where S load - total load power, kVA - number of installed transformers nom.tr - rated power of one transformer, kVA

We check the operation of transformers in emergency mode. Oil transformers allow 40% overload in emergency mode 6 hours a day for 5 days

When one transformer is disconnected, the second, taking into account, will allow overloads:

4 63 \u003d 88.2 kVA

The capacity deficit will be:

1 - 88.2 \u003d 26.9 kVA

but since electrical receivers are consumers of the 3rd category in terms of the reliability of power supply, then some of them can be turned off during the accident

We check the operation of transformers in an economically viable mode

We determine the cost of energy losses by the formula:

С n \u003d С о · N · T m [(ΔР х.х + К и.п · I х.х ·) + К з 2 · (ΔР к.з + К ип · U к ·] (2.23)

where С о - the cost of one kWh, for the current 2013, С о \u003d 0.81 tn / kWh

T m - the number of use of the maximum load, h

K i.p - Coefficient of change in losses, K i.p \u003d 0.03 kW / kvar

ΔР х.х - no-load power losses, ΔР х.х \u003d 0.24 kW х.х - no-load current, I х.х \u003d 2.8%

ΔР short-circuit - short-circuit power losses, ΔР short-circuit \u003d 1.28 kW k - short-circuit voltage, U c \u003d 4.5%

We determine capital costs by the formula:

K \u003d N C tr (2.24)

where C tr is the cost of the transformer, C tr \u003d 31 t

We find the depreciation costs С а:

C a \u003d K a K (2.25)

where K a is the coefficient taking into account deductions for depreciation and operation, for transformers K a \u003d 0.12

We find the total annual costs:

С ∑ \u003d С n + С а (2.26)

For the first option, the results are summarized in table. 2.3

Table 2.3

Parameter name

Option 1 - 1 x 160 kVA

Option 2 - 2 x 63 kVA

ΔР х.х kW

ΔР k.z kW

С о, tn / kW ∙ h

Since C II\u003e C ∑I and K II\u003e K I, then we choose option I - 1 X 160 kVA, as a more economical

5 Choosing the location of the supply substation

The location of the SHR is determined by the cartograms of loads depending on the power of the electrical receivers supplied from it.

It is advisable to install distribution cabinets and a workshop transformer substation in the center of electrical loads (CEN). CEN coordinates are determined by the formula:

X price \u003d (2.27)

Y price \u003d (2.28)

where Хi is the coordinate of the i-th electrical receiver along the abscissa axis, m; - the coordinate of the i-th electrical receiver along the ordinate axis, m;

R nom.i - rated power of the i-th electrical receiver, kW.

We will show the calculation using the example of ШР - 1:

X tseng \u003d \u003d 26.1m tseng \u003d\u003d 8.1m

For the rest of the calculation, similar results are summarized in table 2.4

Table 2.4

Calculated coordinates

Installation coordinates


2.6 Calculation of the 0.38 kV network

workshop power supply lighting transformer

Selection of protection devices

We will show the selection of the conductor cross-section for a separate electrical receiver using the example of a lathe No. 13. We select the cross-section of the supply conductor according to the permissible heating:

add ≥ I p (2.29)

where I add is the permissible current of the conductor, determined by the section

current-carrying core, its material, number of cores, type of insulation and laying conditions, A

The calculated current is determined by the formula:

p \u003d (2.30) p \u003d

this current corresponds to the APV wire - 2.5 mm² with I add \u003d 19A

We check the selected section for permissible voltage losses:

∆U add ≥∆U p (2.31)

where ∆U add - permissible voltage losses, ∆U add \u003d 5%

∆U р - calculated voltage losses,%

∆U р% \u003d (2.32)

where L is the length of the conductor, km o is the active resistance of 1 km of the conductor, r o \u003d 3.12 Ohm / km,

x o - reactance of 1 km of conductor, x o \u003d 3.12 Ohm / km,

since ∆U p< ∆U доп, то сечение 2,5 мм² соответствует допустимым потерям напряжения. В качестве аппарата защиты выбираем предохранитель по следующим условиям:

U number pr > U nom (2.33) nom.pr > I p (2.34) pl.ws > I peak / α (2.35)

where U nom.pr - nominal voltage of the fuse, V nom.pr - nominal current of the fuse, A pl.vs - nominal current of the fuse-link, A peak - peak current, A

α - coefficient taking into account the starting conditions, α \u003d 2.5

peak \u003d K p ∙ I p (2.36)

where K p is the multiplicity of the starting current in relation to the normal mode current

K p \u003d 5 peak \u003d 19 ∙ 5 \u003d 95A nom.pr > 380V nom.pr > 19A pl.vs > 95 / 2.5 \u003d 38A

We choose a fuse PN - 2, I nom \u003d 100A I pl.vs \u003d 40A

We check the selected wire for compliance with the selected fuse according to the condition:

add ≥ К z ∙ I z (2.37)

where K z is the multiplicity of the permissible current of the conductor in relation to the operating current of the protection device, K z \u003d 1

I s - protection operation current, A

since nineteen< 1 ∙ 40, то провод не соответствует аппарату защиты поэтому выбираем провод АПВ - 10мм 2 , I доп = 47А

We will show the calculation for a group of electrical receivers using the example of ShR-1

In accordance with the formula (2.30) I p \u003d 67.82A. According to the condition (2.29), select the AR wire - 25mm 2; I add \u003d 80A

By formula (2.32) we find:

∆U p% \u003d 0.2%

Wire APV-25mm 2 corresponds to the permissible voltage loss,

since ∆U p \u003d 0.2% ≤ ∆U add \u003d 5%

We install a fuse as a protection device.

Find the peak current:

peak \u003d I p - K and ∙ I nb + I start. nb (2.38)

where I nb is the rated current of the largest motor in terms of power, powered by the ShR-1 start-up; nb is the starting current of the largest motor in terms of power, powered by the ShR-1

According to the formula (2.30) we find I nb \u003d 91A, by the formula (2.36) I start.nb \u003d 455A peak \u003d 67.82 - 0.13 91 + 455 \u003d 511A

According to the conditions (2.33), (2.34), (2.35), we select the PN-2 fuse with nom.pr \u003d 250A, I pl.vs \u003d 250A

Checking the selectivity fuse

The single-line diagram of ShR-1 is shown in Fig. 2.1

Fig. 2.1 Single-line diagram ШР-1

The fuse at the input is not selective, therefore we select the PN-2 fuse I nom.pr \u003d 400A, I pl.ws \u003d 350A

We check the selected wire for compliance with the selected fuse according to the condition (2.37), because 67.82 ≤ 1 ∙ 350, then the wire does not correspond to the protection device, therefore we choose the cable SB 3 185 + 1 95 s I add \u003d 340A

Taking into account the permissible overload, the cable corresponds to the selected fuse.

For the rest of the electrical receivers and distribution cabinets, the calculation is similar, the results are summarized in table. 2.5

Table 2.5

conductor

fuse

Number of lived




2.7 Calculation of the network with voltage above 1 kV

We determine the economically feasible section using the formula:

F eq \u003d (2.39)

where j eq is the economic current density, j eq \u003d 1.7 A / mm 2

In accordance with formula (2.30): p \u003d A eq \u003d 9m

We choose the nearest standard section - 10 mm²

Choosing a cable AAB-3x10 mm 2

We check the selected cable for thermal resistance to short-circuit currents

The thermally stable cross-section to short-circuit currents is determined by the formula

m.y. \u003d (2.40)

where I ∞ is the steady-state value of the periodic component of the short-circuit current ∞ \u003d 2850A (see Section 2.8)

С - coefficient taking into account the difference in heat released by the conductor before and after a short circuit, С \u003d 95

t pr - fictitious time at which the steady-state short-circuit current releases the same amount of heat as the actual short-circuit current. for real time

at tg \u003d 0.15 s, t pr \u003d 0.2 s, at β '' \u003d 2 T. y \u003d 2850 \u003d 13

AAB cable 3 x 10 is thermally resistant to short-circuit currents

Finally, we choose the AAB cable 3 x 10

2.8 Calculation of short-circuit currents

The calculation is carried out in relative units under basic conditions. In accordance with the assignment and design results, we draw up a design diagram and an equivalent circuit. The design circuit is given in Figure 2.2, the equivalent circuit in Figure 2.3

Fig. 2.2 Design diagram Fig. 2.3 Equivalent circuit

Let us assume that the base power Sb \u003d 100 MVA, the base voltage Ub \u003d 6.3 kV

Overhead line resistance is found by the formula:

X vl * b \u003d (2.41)

where U nom.av - average rated step voltage, kV

X vl * b \u003d 0.4 · 35 · 100 / 115² \u003d 0.11 Ohm

The transformer resistance is found by the formula:

tr.b \u003d * (2.42) tr.b \u003d * \u003d 4.2 Ohm

We determine the reactance of the cable line according to the formula (2.41):

X cl * b \u003d \u003d 0.28 ohm

We find the active resistance of the cable line by the formula

(2.43) cl * b \u003d = 7,97

Using the signs of parallel and series connection of resistances, we find the active and inductive resultant resistances:

X res * b \u003d 0.11 + 2.1 + 0.28 \u003d 2.49 res * b \u003d 7.97

because k \u003d res * b = 8,35

Determine the short-circuit current by the formula:

where I b - base current, kA

Using the formula (2.14), we find the base current:

I b \u003d \u003d 9.16 kA

I short-term \u003d \u003d 1.1kA

Determine the shock current:

y \u003d (2.45) y \u003d 2.55 ∙ 1.1 \u003d 2.81 kA

Find the short-circuit power:

k.z. \u003d (2.46) short-circuit. \u003d \u003d 11.98 MVA

9 Selection of substation equipment

We select disconnectors according to the following conditions:

no.r > U number. (2.47) no. > I calc. (2.48) a. ≥ i y. (2.49)

I t ² ∙ t > I to 2 ∙ t pr (2.50)

where U nom.r is the rated voltage of the disconnector

I nom.r - rated current of the disconnector a - peak value of the preliminary through current short-circuit t - limiting thermal current - time during which the disconnector withstands the limiting thermal current

Find the nominal data of the disconnector by

The choice of the switch is made according to the following conditions:

nom.w \u003d U nom (2.51) nom.v > I p (2.52) a. ≥ i y (2.53) t ² ∙ t > I to 2 ∙ t pr (2.54) open > I to (2.55) open ≥ S to (2.56)

where U nom.v - rated voltage of the circuit breaker, kV nom.v - rated current of the circuit breaker, A open - rated breaking current of the circuit breaker, kA open - breaking power of the circuit breaker, MVA

open \u003d ∙ I open ∙ U nom.v (2.57)

We find the nominal data of the oil switch. The selection results are presented in table. 2.6

Table 2.6


3. SAFETY AND LABOR PROTECTION

1 Organizational and technical measures for the safe performance of work with electrical installations up to 1 kV

For the safe conduct of work, the following organizational measures must be performed:

appointment of persons responsible for the safe conduct of work;

issuance of an order and order;

issuance of a permit for the preparation of workplaces and for admission;

workplace preparation and admission;

supervision while performing work;

transfer to another workplace;

registration of breaks in work and its completion.

All work, both with and without voltage relief, near or on live parts must be carried out according to a permit or by order, since ensuring their safe performance requires special preparation of the workplace and the implementation of certain measures. The exception is short-term and small-scale work performed by the duty or operational-repair personnel in the order of current operation. Their duration should not exceed 1 hour.

One worker can be the one preparing the workplace and the admitting one.

An attire is a task drawn up on a special form for the safe production of work, which determines the content of the work, the place, the time of its beginning and end, the necessary safety measures, the composition of the team and persons responsible for the safety of the work. The outfit can be issued for up to 15 days.

An order is a task for the safe production of work, which determines the content of the work, place, time, security measures for persons who are entrusted with its implementation. The order can be verbal or written, it has a one-time character. Work with a duration of up to 1 hour is allowed to be performed by order of the repair personnel under the supervision of the duty officer or a person from the operational and repair personnel, as well as the most on-duty or operational repair personnel. In this case, the senior person performing work or leading supervision must have qualification group IV in electrical installations with voltages above 1000 V. If the duration of these works is more than 1 hour or they require the participation of more than three people, then they are issued in an attire.

The issuing outfit, the order establishes the possibility of safe performance of work. He is responsible for the sufficiency and correctness of the safety measures specified in the order, for the qualitative and quantitative composition of the team and the appointment of responsible persons, as well as for the compliance of the work performed by the electrical safety groups of the workers listed in the order. The right to issue orders and orders is granted to employees from the administrative and technical personnel of the enterprise and its structural divisions who have group V.

The work manager is responsible for the implementation of all safety measures specified in the order and their sufficiency, completeness and quality of the instructions of the brigade carried out by the admitting and manufacturer of the work, as well as the organization of the safe conduct of work. Engineering and technical personnel with group V should be appointed as work supervisors.

The person who gives permission for the preparation of workplaces and for admission is responsible for the sufficiency of the measures provided for the work to disconnect and ground the equipment and the possibility of their implementation, as well as for the coordination of the time and place of work of the admitted teams. Employees from duty personnel with group IV in accordance with job descriptions, as well as employees from administrative and technical personnel authorized to do so by instructions for the enterprise, have the right to give permission for the preparation of workplaces and for admission.

The person preparing the workplace is responsible for the correct and accurate implementation of the measures for preparing the workplace specified in the order, as well as those required by the working conditions (installation of locks, posters, fences).

The duty officer or workers from the operational and repair personnel who are admitted to operational switching in this electrical installation have the right to prepare workplaces.

The admitting person is responsible for the correctness and sufficiency of the safety measures taken and their compliance with the measures specified in the attire, the nature and place of work, for the correct admission to work, as well as for the completeness and quality of the instructions given by him. The admitting agent must be appointed from the duty or operational-repair personnel. In electrical installations above 1000V, the admitting one must have group IV. The manufacturer of work performed alongside in electrical installations above 1000V must have group IV. A supervisor should be assigned to supervise teams of workers who are not allowed to independently work in electrical installations. Workers with group III can be appointed as observers.

Each member of the team is obliged to comply with the safety rules for the operation of electrical installations and instructions received upon admission to work and during work, as well as the requirements of local labor protection instructions.

CONCLUSION

When designing a mechanical repair shop, the following results were obtained:

1. A variant of the power supply scheme has been selected, a power distribution network scheme has been developed

2. In accordance with the power and lighting loads, taking into account economic indicators for the power supply of the production workshop, it is necessary to install one transformer with a capacity of 160 kVA at the 6 / 0.4 kV supply substation

It is advisable to perform power networks 0.38 kV with an AAB cable laid along cable structures, and an automatic reclosure wire laid in pipes in the floor

Fuses must be selected as protection device

5. The organizational and technical measures for labor protection during work in electrical installations up to 1 kV are given

The design results are given in the table:

Name of electrical equipment

Brand Type

unit of measurement

amount

Three-pole disconnector

Oil switch

VMM-10-320-10tz

Oil transformer with a capacity of 160 kW * A

Fuse

also I nom \u003d 600A I pl.vs \u003d 500A

also I nom \u003d 250A I pl.vs \u003d 200A

also I nom \u003d 250A I pl.vs \u003d 120A

also I nom \u003d 100A I pl.vs \u003d 80A

also I nom \u003d 100A I pl.vs \u003d 50A

also I nom \u003d 100A I pl.vs \u003d 40A

also I nom \u003d 100A I pl.vs \u003d 30A

Cable for voltage 6KV with a cross-section of 3 / 10mAPV

Postnikov N.P., Rubashov G.M. Power supply for industrial enterprises. L .: Stroyizdat, 1980.

Lipkin B.Yu. Power supply of industrial enterprises and installations. - M .: Higher school, 1981.

Kryuchkov I.P., Kuvshinsky N.N., Neklepaev B.N. Electrical part of stations and substations.- Moscow: Energiya, 1978.

6. Handbook of power supply and equipment / Ed. Fedorova A.A., Barsukova A.N. M., Electrical equipment, 1978.

7. Rules for the arrangement of electrical installations / USSR Ministry of Energy. - M .: Energiya, 1980.

Khromchenko G.E. Design of cable networks and wiring - M .: Higher school, 1973.

9.E.F. Tsapenko. Devices for protection against single-phase earth fault. - M .: Energoatomizdat 1985 - 296 p.

10. Shidlovsky A.K., Kuznetsov V.G. Improving the quality of energy in electrical networks. - Kiev: Naukova Dumka, 1985 - 354 p.

Zhelezko Yu.S. Choice of measures to reduce electricity losses in electrical networks. A guide for practical calculations. - M .: Energoatomizdat, 1989 - 176 p.

Electrical networks are used to transmit and distribute electrical energy to shop floor consumers of industrial enterprises. Energy consumers are connected through in-house substations and switchgears using protective and starting devices.

The electrical networks of industrial enterprises are carried out by internal (workshop) and external. External voltage networks up to 1 kV are of very limited distribution, since in modern industrial enterprises, the power supply of shop loads is produced from in-shop or attached transformer substations.

The choice of electrical networks radial power supply circuits are characterized by the fact that from the power source, for example, from a transformer substation, there are lines that directly feed powerful electrical receivers or separate distribution points, from which smaller electrical receivers are fed by independent lines.

Radial circuits provide high reliability of power supply to individual consumers, since accidents are localized by disconnecting the circuit breaker of the damaged line and do not affect other lines.

All consumers can lose power only in case of damage on the KTP busbars, which is unlikely. As a result of the rather reliable design of these KTP cabinets.

Trunk power supply circuits are widely used not only for powering many electrical receivers of one technological unit, but also for a large number of comparisons of small receivers that are not connected by a single technological process.

Trunk circuits allow you to abandon the use of bulky and expensive switchgear or switchboard. In this case, it is possible to use a transformer-main block diagram, where busbars (busbars) manufactured by the industry are used as a supply line. Trunk circuits made by bus ducts provide high reliability, flexibility and versatility of shop networks, which allows technologists to move equipment within the shop without significant installation of electrical networks.

Due to the uniformity of distribution of consumers within the mechanical repair shop, as well as low cost and ease of use, a main power supply scheme is selected.

The location of the main equipment is shown in the diagram (Fig. 1).

The choice of a 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 consumers are divided into the following three categories.

Electrical receivers first category - electrical receivers, an interruption in the power supply of which may entail a danger to human life, a threat to the security of the state, significant material damage, disruption of a complex technological process, disruption of the functioning of especially important elements of communal services, communication and television facilities.

A special group of electrical receivers is distinguished from the composition of power consumers of the first category, whose uninterrupted operation is necessary for a trouble-free shutdown of production in order to prevent threats to human life, explosions and fires.

Electrical receivers second category - electrical receivers, the interruption of the power supply of which leads to a massive undersupply 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 consumers that do not fall under 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 a break in their power supply in the event of a power failure from one of the power sources can be allowed only for the time of automatic power restoration.

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

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

If the power supply backup cannot ensure the continuity of the technological process or if the power supply backup is economically inexpedient, technological backup should be carried out, 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 failure.


Power supply to power consumers of the first category with a particularly complex continuous technological process that requires a long time to restore normal operation, in the presence of feasibility studies, is recommended to be carried out from two independent mutually redundant power sources, to which additional requirements are imposed, determined by the characteristics of the technological process.

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

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

For electrical receivers of the third category, power supply can be performed from one power source, provided that the power supply interruptions required for repair or replacement of a damaged element of the power supply system do not exceed one day.

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

To power industrial enterprises, power grids with a voltage of 6, 10, 20, 35, 110 and 220 kV are used.

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

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

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

There are two main schemes of electric power distribution - radial and main, depending on the number and relative position of shop substations or other electronic devices in relation to the point supplying them.

Both schemes provide the required reliability of power supply for any category of electronic devices.

Radial distribution schemes are mainly used when 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 shop substations. Two-stage radial circuits are used to power small shop substations and high voltage power consumers in order to unload the main energy centers (Fig. H.1). All switching equipment is installed at intermediate distribution points. Avoid the use of multi-stage circuits for intra-shop power supply.

Distribution points and substations with power consumers of categories I and II are fed, as a rule, through two radial lines, which operate separately, each to its own section, when one of them is disconnected, the load is automatically taken over by the other section.

Fig. 3.1. Fragment of a radial power distribution diagram

Trunk distribution schemes of electricity should be used with distributed loads, when there are many consumers and radial schemes are economically impractical. The main advantages: allow better loading of cables during normal operation, save the number of cabinets at the distribution point, reduce the length of the trunk. The disadvantages of trunk circuits include the complication of switching circuits, the simultaneous shutdown of the electric power supply of several production sites or workshops powered by this trunk when it is damaged. To supply power supply of I and II categories, circuits with two or more parallel through lines should be used (Fig. 3.2).

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

The choice of two-transformer KTP should be justified. The most expedient and economical for intrashop power supply in networks up to 1 kV are the main circuits of the transformer-main blocks without switchgear at the substation using complete busbars.

Radial circuits of intrashop supply networks are used when it is impossible to execute trunk circuits due to the conditions of territorial distribution of electrical loads, as well as environmental conditions.

For the power supply of workshop consumers in design practice, radial or trunk circuits are rarely used in their pure form. The most widespread are the so-called mixed circuits of electrical networks, combining elements of both radial and trunk circuits.

Fig. 3.2. Dual loop through circuit

Power supply circuits and all electrical installations of alternating and direct current of an enterprise with a voltage of up to 1 kV and above 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 case of insulation damage.

Electrical installations with regard to electrical safety measures are divided:

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

- electrical installations with a voltage higher than 1 kV in networks with an insulated 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 isolated neutral.

For electrical installations with voltage up to 1 kV, the following designations are adopted. System TN - a system in which the neutral of the power supply is solidly grounded, and the open conductive parts of the electrical installation are connected to the solidly grounded neutral of the source by means of zero protective conductors (Fig. 3.3-3.7).

Fig. 3.3. System TN-C - system TNin which the zero protective

and neutral working conductors are combined in one conductor

throughout its entire length

The first letter is the state of the neutral of the power supply 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 relationship to the ground of the neutral of the power supply or any point of the supply network;

N - exposed conductive parts are connected to the dead-grounded neutral of the power supply.

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

S - zero worker ( N) and zero protective ( PE) the conductors are separated;

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

N - zero working (neutral) conductor;

PE - protective conductor (grounding conductor, neutral protective conductor, protective conductor of the equipotential bonding system);

PEN - combined zero protective and zero working conductor.

Zero working (neutral) conductor ( N) - a conductor in electrical installations up to 1 kV, designed to power electrical receivers and connected to a dead-grounded neutral of a generator or a transformer in three-phase current networks, with a dead-grounded outlet of a single-phase current source, with a dead-grounded source point in DC networks.

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

To protect against electric shock during 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;

- the use of ultra-low (low) voltage.

Fig. 3.4. System TN-S - system TNin which the zero protective

and zero working conductors are separated along its entire length

Fig. 3.5. System TN-C-S - system TNin which functions of zero

protective and neutral working conductors are combined in one

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

Fig. 3.6. System TT - a system in which the neutral of the power supply

solidly grounded, and exposed conductive parts of the electrical installation

grounded by a grounding device, electrically

independent of a solidly grounded neutral source

Fig. 3.7. System IT- a system in which the neutral of the power supply

isolated from earth or grounded through appliances or devices,

high resistance, and exposed conductive parts

electrical installations are grounded

For additional protection against direct contact in electrical installations with voltages up to 1 kV, if the requirements of other chapters of the PUE are required, apply 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 against 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, platforms.

Electrical installations with voltages up to 1 kV in residential, public and industrial buildings and outdoor installations should, as a rule, be powered from a source with a solidly grounded neutral using a 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, when it is inadmissible to interrupt the power supply at the first earth fault or to open conductive parts associated with the potential equalization system. In such electrical installations, for protection against indirect contact during the first earth fault, protective grounding must be performed in combination with network insulation monitoring or an RCD with a rated residual current of not more than 30 mA must be used. In case of a double earth fault, an automatic power off must be performed 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 an earthing switch not connected to the neutral (system TT), is allowed only in cases where the electrical safety conditions in the system T N cannot be provided. For protection against indirect contact in such electrical installations, an automatic power off must be performed 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 ground electrode and the grounding conductor of the most distant electrical receiver when using an RCD to protect several electrical consumers.

When applying the system TN re-grounding is recommended PE- and PEN-conductors at the entrance to electrical installations of buildings, as well as in other accessible places. For re-grounding, first of all, natural grounding conductors should be used. Re-grounding resistance 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 the power supply diagrams of individual buildings, and in app. 4 - graphic and letter symbols in electrical circuits.

 

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