Diploma project of the repair and mechanical plant

Summary

The diploma project has developed a power supply system for a mechanical repair plant. In the project, electrical loads were calculated using the RELNA program developed at the Department of Power Supply of Industrial Enterprises. The rational power supply scheme of the enterprise was also chosen on the basis of technical and economic indicators. Short-circuit currents are calculated and electric devices are selected in accordance with them. The issues of reactive power compensation in the selection of transformers are also considered. The necessary requirements of occupational safety and safety during power supply of the mechanical plant are described in this project.

The topic was developed in depth: "Study of the effect of voltage deviation on the operation of electric receivers."

Introduction

In the country, electric energy consumption (EE) is increasing every year. The increase in the demand for electric energy is due not only to growth, but also to qualitative changes in all sectors of the national economy.

Industrial enterprises are the main consumers of electricity, as they spend about 70% of all electricity generated in our country.

The power supply system of enterprises, consisting of networks of voltages up to 1000 V and above, transformer and converter substations, serves to meet production requirements by supplying electricity from the power source to the place of consumption in the required amount and of appropriate quality in the form of alternating, single-phase or three-phase, at various frequencies and voltages or direct current.

Modern enterprises are characterized by the dynamic process associated with the continuous introduction of new processing methods, new equipment, its re-installation, as well as continuous change and improvement of the process.

Therefore, we should strive to create an enterprise with sufficient flexibility, which allows with the least losses to carry out a restructuring of production when changing the program or modernizing products, introducing the latest technological processes and modern equipment, as well as automation

production. The main tasks solved during the study, design of power supply of industrial enterprises are to optimize parameters by correct selection of voltage, determination of electrical loads and requirements for uninterrupted power supply, rational selection of number and

power of transformer substations, conversion of current and frequency, design of industrial networks, means of reactive power compensation and voltage control, load symmetry and suppression of higher harmonics in networks by correct construction of a power supply circuit corresponding to the optimal level of reliability.

Complete switchgears, complete substations, complete power and lighting conductors are widely used in the workshop power distribution system. This creates a flexible, reliable distribution system, giving a great economic effect.

The general task of optimizing industrial power supply systems, in addition to the above provisions, also includes a rational solution for choosing automation and dispatching methods. At the same time, the choice of a rational operating mode of the enterprise should be made, assessing the economic efficiency of the entire enterprise.

2 characteristics of the environment and category of consumers according to the degree of reliability of the power supply

All electrical equipment is located in the production room, the medium can be characterized as normal. In this sense, all equipment is in favorable conditions. The exception is the blacksmith shop, as well as the foundry. According to the rules of electrical installations (PUE), blacksmith and foundry shops [8] can be attributed to hot rooms.

According to PUE, from the point of view of uninterrupted power supply, there are three categories of electric receivers (EP):

- First category EPs, the disturbance of the power supply of which can cause danger to human life or significant material damage due to equipment damage, mass breakdown of products or long-term disorder of complex production process.

- EP of the second category, the interruption of power supply of which is associated with significant underfilling of products, downtime of people, mechanisms.

- third category EP, receivers not suitable for definitions of the first and second category, for example, receivers of secondary workshops that do not define the main production process.

At the experimental mechanical plant, metal cutting machines are mainly located. According to the degree of uninterrupted power supply, the plant belongs to the third category, with the exception of several large workshops, where a break in power supply is unacceptable due to possible damage to products, especially when processing large expensive parts. These machines can be classified in the second category.

So, from the point of view of reliability of power supply, the main and auxiliary equipment of the mechanical plant belongs to the second and third categories.

4 current and voltage selection

Current selection for power supply systems is related to selection of optimal type of DC or AC electric drive. In electrical installations of industrial enterprises, three-phase alternating current with a frequency of f = 50 Hz finds the most use.

Finding a rational voltage value for an industrial plant system means determining the standard voltage level at which the system has a minimum annual estimated cost. These minimum annual costs at the same time must correspond to the minimum possible costs of material assets: the amount of non-ferrous metal, equipment, power losses, etc.

The main AC electric receivers at the mechanical plant are 380 V AC motors. To power these electric receivers, 0.4 kV is the most economical. At the same time, the consumption of non-ferrous metal is significantly reduced compared to a voltage of 220 V, with the same power of the electric current receiver 0.3 times less than in the 220 V network.

10 and 6 kV voltages are widely used in industrial enterprises - for supply and distribution networks; at large enterprises - at the second and subsequent stages of electricity distribution.

A voltage of 10 kV is more economical than a voltage of 6 kV. 6 kV is allowed to be used only if power receivers with a nominal voltage of 6 kV prevail at the enterprise or when a significant part of the plant load is supplied from the factory CHP, where 6 kV generators are installed.

So, we choose the voltage of the intra-plant distribution network

equal to 10 kV .

Voltage selection for lighting installations is related to selection of power supply system for power and lighting consumers from common or separate transformers. Taking into account the prohibition of the use of 220/127 V voltage for enterprises, the 380/220 V variant is possible, the power and lighting receivers are jointly powered from common transformers.

When combining power supply from common transformers, there are negative factors. For lighting, the value of voltage fluctuations of not more than 1.5% at the frequency of voltage fluctuations of not more than 10 times per hour is allowed, which means that lighting consumers must be connected to those sections of buses where there are no shock loads.

To power the power consumers of the mechanical plant, we select a voltage of 380 V. To power the lighting plants, we provide for the use of a voltage of not more than 250 V relative to the ground, so the question arises of the need for a blind grounding of the neutral 380/220 V. In this case, any single-phase ground fault leads to the disconnection of one phase or all three phases.

5 choice of place of installation of shop transformer substations

In-house substations can be located on the first and second floors, in the main and auxiliary rooms of the production, which are assigned according to fire requirements to rooms of category I or II of fire resistance, both in open and in separate rooms [1].

The type and location of the substation, their number and power, as well as the voltage of the supply and distribution networks are selected in the following sequence :

- on the schematic plot plan of production, loads of individual objects or sections of the workshop with a subdivision by voltage, type of current and order of commissioning are applied;

- loads are denoted in the form of circles with radii corresponding to loads on a certain scale with the application of digital values of loads inside them;

- detecting concentrated loads and determining centers of distribution load groups;

- pre-scheduling substation locations;

- load distribution is performed between them taking into account scattered loads gravitating to them or separate substations are marked for the latter [9].

It is impossible to place under rooms with a wet process, under showers, latrines, and when this is inevitable, it is necessary to do waterproofing of substations ceilings.

It is recommended to place in-house substations mainly at columns or near any permanent workshop premises so as not to occupy crane tracks. When substations are forced to be placed close to internal transport or crane tracks, telpheres and other lifting and transportation mechanisms

Measures shall be taken to protect them from accidental damage by means of a light-signalling device, breakage pedestals and other measures. Internal substations are recommended to be located in the dead zone of cranes and other lifting mechanisms.

Particular attention should be paid to the cost-effective construction and installation of substations, having agreed with the required degree of reliability of power supply for this production. Industrial methods of construction and installation of substations shall be provided using large-unit devices and assembly units, pre-manufactured in purchase workshops, electrical installation organizations and in electric industry plants.

There should be no excesses in the circuit and structural parts, unreasonable use of expensive automation.

When performing the construction part of substations and other electrical rooms, light industrial structures are used. They are pre-fabricated outside the mounting area and assembled in situ.

Complete transformer substations (KTP) in our case are located inside the production premises and are attached to the walls in accordance with the placement of the necessary electrical equipment and taking into account the movement of in-plant transport .

9.1 Overview of Short Circuits

The main reason for the failure of the normal operation of the power supply system is the occurrence of a short circuit in the network or in the electrical equipment elements, due to damage to the insulation or incorrect actions of the maintenance personnel. In order to reduce the damage caused by the failure of electrical equipment during short circuit currents, as well as to quickly restore the normal operation of the power supply system, it is necessary to determine short circuit currents and select electrical equipment, protective equipment and short circuit current limitation devices from them.

In a three-phase network, the following types of short circuits are distinguished: three-phase, two-phase, single-phase and single-phase on earth.

The design type of short circuit for selecting and checking the parameters of electrical equipment is usually considered a three-phase short circuit. The calculation of short-circuit currents taking into account the actual characteristics and actual operating modes of all elements of the power supply system is complex. Therefore, to solve most practical problems, assumptions are introduced that give insignificant errors:

a) phase shift of electromotive force (EMF) of various power sources included in the design circuit is not taken into account;

b) three-phase network is considered symmetrical;

c) load currents are not taken into account;

d) capacitance and therefore capacitive currents in cable lines are not taken into account;

e) saturation of magnetic systems is not taken into account, which makes it possible to consider inductive resistances of all elements of short-circuited circuit as constant and independent of current;

f) magnetization currents of transformers are not taken into account.