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Table of contents   Introduction………………………………………………………………………..3

1. Types of power supply ………………………………………………………….4
2. Selection of voltage distribution networks …………………………………….8
3. The main requirements for the power supply system of the city ………………10
4. Perfect power supply system of the city …………………………………….…13

Conclusion………………………………………………………………….…….16   Introduction   Due to the acceleration of scientific and technological progress, the consumption of electricity in industry has increased significantly due to the creation of flexible automated production facilities. The energy program provides for the creation of powerful territorial production complexes in those regions where large reserves of mineral and water resources are concentrated. Such complexes extract, process, transport energy resources, using in their activities various electrical installations for the production, transmission and distribution of electric and thermal electricity. The first place in the amount of electricity consumed belongs to industry, which accounts for more than 60% of the energy produced in the country. With the help of electric energy, millions of machines and mechanisms are set in motion, lighting of premises, automatic control of technological processes and so on is carried out. There are technologies where electricity is the only energy source. Modern energy is characterized by increasing centralization of electricity production and distribution. The energy of the system consists of several large interconnected power systems. In the near future, the energy sector faces the task of all-round development and use of renewable energy sources: solar, geothermal, wind, tidal, etc.; development of combined power generation and heat for district heating of industrial cities. The subject is electricity supply. The object is the power supply of the city. The main purpose of the work is to study the ideal power supply system of the city. To achieve this goal it is necessary to solve the following tasks: — to consider the types of power supply; — to consider the basic requirements for the city’s power supply system.  

1. Types of power supply

  Distinguish:

• city power supply;
• power supply of residential and public buildings;
• power supply of intelligent buildings (computer and telecommunication systems);
• power supply of enterprises;
• centralized power supply;
• decentralized power supply.

  Power supply of the city The system of power supply of the city is understood as a set of electric networks and transformer substations located in the territory of the city and intended for power supply of its consumers. The system is limited on the one hand by power sources, on the other hand-inputs of electric networks to consumers. Local power plants and step-down substations with a voltage of 35-110 kV and above are used as power sources, which are powered in turn from the electric networks of power systems. The main indicators of the system are determined by local conditions: the size of the city, the availability of power sources, the characteristics of consumers, etc. The power supply system of a small city can have the form indicated in Fig.1. For power supply of the city the local power station and the regional substation feeding from a power system are provided [5]. Typically, these power sources are also used for power supply of industrial enterprises located near the city. Power of urban consumers by means of distribution networks with voltage 6-10 kV and 0.38. The distribution network of 6-10 kV runs on a loop diagram; in normal mode, open loop. Fig.1. Simplified block diagram of power supply of the city   Transformer substations TS with transformers of different power supply distribution network 0,38 kV (public network), which is performed depending on the nature of consumers. For the supply of industrial enterprises and municipal consumers, independent substations of the TSI may be provided, which are not connected with the public network. Depending on the responsibility of the consumer, TS can be automated, i.e. equipped with devices for automatic switching of the consumer’s power supply to the backup line in case of a sudden exit from the main line. As the size of the city increases, the distribution network of 6-10 kV becomes insufficient to cover all consumers located in its territory [3]. Additional elements are introduced into the power supply system, in particular the 6 — 10 kV supply network, as well as higher voltage networks. Among the consumers of the city there are also large industrial consumers, whose power supply is carried out by separate supply lines of 6-10 kV and transformer distribution substations of TDS. TDS supplies the 6-10 kV in-plant distribution network. Similarly, the power supply of large municipal enterprises, such as the main water supply station, tram substations, etc., usually belonging to category I electric receivers, is also carried out by means of independent supply networks of 6-10 kV, based on different power sources [1]. The power supply system of a large city is characterized by a large number of power sources and their capacity. The power supply of the central districts of the city at the expense of networking intermediate voltage of 35 kV and urban substations 35/6-10 kV. The 35 kV network is, as a rule, reserved for the radial scheme. Substations 35/6-10 kV have developed distribution devices (DD) 35 kV and their capacity can reach 30-40 MVA depending on the size of the city. The 6-10 kV distribution network is characterized by an even greater degree of automation. Power supply of large industrial consumers can be carried out at higher voltages than 6-10 kV. Since the power supply system of a large city, contains a large number of power sources and networks of different voltages, the exact definition of the boundaries of the system from the high voltage presents certain difficulties, since some of its elements can be attributed to the elements of the power system. Fig.2. Power supply system of a large city   The parameters of the 110 kV ring network between substations I to II are determined only by the power supply conditions of consumers of the city, if we mean substation IV (Fig.2). On the other hand, it is necessary to take into account the conditions of the power system, since, in addition to urban substations III and VI, the power plant VII is also connected to the ring network. From the above it follows that the main indicators of the power supply system of the city are determined by its size, the conditions of the power system, the characteristics of consumers and other local features [7]. Let’s clarify the names of the main elements of the system. The electric network of 35-110 kV and above, including step-down substations of the same voltage, is called the power supply network. It includes a network that links power supplies and distributes energy between areas of the city, and a network used to supply high voltage to central areas or directly to large consumers of the city.

The first network is in the form of a ring, covering the city, and for this reason can be called a ring network. The second is called the deep input network. According to the EIR (Electrical Installation Regulations), a deep input is a power supply system with an approximation of the highest voltage to the electrical installations of consumers with the least number of intermediate transformation stages and devices. The circuit of the ring network is determined by local conditions and can be quite complex. Deep network of 35-110 kV bushings regardless of the characteristics of the city is, as a rule, for a simple scheme of two mutually redundant radial lines 35-110 kV. In the systems with the three voltages of the network of intermediate voltage of 35 kV in the presence of a ring network of 110 kV and above is essentially a network of deep input.

According to the specified division of networks it is possible to distinguish step-down substations: the primary or basic substations connecting a power system and generating sources to a ring network; ring substations and substations of deep input; secondary step-down substations of intermediate voltage of 35 kV-in their presence. Parameters, schemes and constructive performance of these substations are determined by their place in the power supply system of the city. According to the EIR, a distribution line, which is an element of the distribution network, is a line that feeds a number of TS from the power center or RP, or inputs to the electrical installations of consumers. A supply line is a line that feeds a DF or substation from a power center, without distributing electricity along its length. A distribution point (DF) is a substation of an industrial enterprise or an urban electric network designed to receive and distribute electricity at a single voltage without its conversion and transformation. The analysis of principles of construction of systems of power supply of the cities allows to establish the main tasks arising at a choice of rational implementation of such systems [4]. These include: the selection scheme of construction of system; voltage networks and the number of transformations of energy; definition of optimal parameters of the main elements of the electricity supply and distribution networks. If the principle of construction of the system is determined by the local characteristics of the city, including the characteristics of power sources, voltage of electric networks of the power system, the geographical location of the city, etc., the solution of other issues allows a generalized approach, regardless of local conditions. All these issues of rational implementation of the city power supply system have a technical and economic nature, and therefore their solution should be based on the use of appropriate methods of technical and economic calculations.

2. Selection of voltage distribution networks

  The choice of voltage of urban distribution networks is made, as a rule, in accordance with the recommendations of VSN 97-83. In some cases, feasibility studies may be required When choosing the voltage in all cases, it is necessary to take into account the prospect of development of distribution networks within the estimated period of the master plan of the city. Networks up to 1000 V should be performed three-phase four-wire with a blind grounding neutral voltage 380/220 V. when reconstructing existing networks 220/127 V and 3×220 V should be switched to a voltage of 380/220 V. the use of existing three-core cables and their lead or aluminum shells as the fourth core. Urban electric networks with voltage above 1000 V should be three-phase with isolated neutral, as a rule, at a voltage not lower than 10 kV. when expanding or reconstructing existing networks of 6 kV, it is recommended to transfer them to a voltage of 10 kV using installed equipment and 6 kV cables. At a generator voltage of 6 kV, it is advisable to provide electricity to the areas adjacent to the power plant at the same voltage. For more remote areas, in which the power supply circuit has an additional voltage stage 35-110 kV, distribution networks should be provided at a voltage of 10 kV. At existing district substations with a secondary voltage of 6 kV, it is possible to provide for the installation of additional step-down transformers with a voltage of 10 kV or three-winding transformers 110/10/6 kV. The presence of three-winding transformer substation 110/10/6 kV additional transformer winding: 10 kV will at the same time with the implementation of the new distribution networks and translate existing network of 6 kV to 10 kV. Urban distribution networks 6-35 kV must be performed three-phase with insulated or grounded through arcing devices neutral. Requirements to compensation of capacitive currents in these networks are specified in the same place.

3. The main requirements for the power supply system of the city

  Until now, we have considered the issues of rational construction of the system in the scope of solving specific problems, for example, identifying the technical and economic features of individual elements of power supply. In the power supply system of the city, the elements represent a single whole, so the choice of rational construction of the system includes a set of issues, in the process of consideration of which the required ratios between the individual elements of the system must be found, so that its total technical and economic indicators are within the most favorable limits, while taking into account the local characteristics of the city. In defining rational ways of building a supply system sets out the General principles of its implementation, configuration of networks of accepted voltages, layout of substation and power sources, the order of construction of individual elements of the system, the choice of power supply (i.e. the definition of the necessary electrical connections between all elements of the system). The scheme of power supply of the city in the first place should be based on the established optimal parameters and voltage levels of individual elements of the system, as well as the number of energy transformations. It should take into account that some elements of the power supply system of the city are both elements of power system area, i.e., with their help, can provide for parallel operation of power grid and implementation of the necessary modes of its work. It should be taken into account that the system is designed to supply energy to a very large number of consumers. Thus the choice of the scheme of power supply of the city is made irrespective of character of consumers and the required level of reliability of supply of their receivers of energy [2]. Only the total power of consumers is the criterion by which the level of reliability of their power supply is determined. In particular, the set of receivers of all categories with a capacity of more than 10 MVA belongs to the receivers of category I. The aggregate capacity from 400 kV-A to 10 MVA when performing networks by cables is a category II receiver (with the exception of category I receivers). The scheme of power supply of the city is based on the specified power sources. At the same time, on the one hand, sources for the supply of individual urban areas and large consumers in the form of urban or industrial substations should be selected. On the other hand, the sources intended directly for the power supply system of the city — district substations of the power system-should be installed. The main feature of the city’s electricity consumption is its continuous increase both due to natural growth and due to new consumers. The reliability of power supply created by the system must be within the limits regulated by the EIR, which establishes the volume of reserve elements of the system to provide power to consumers of the city at full capacity under various modes of its operation. The choice of design modes is made according to the requirements of the relevant sections of the EIR, taking into account planned and emergency shutdowns of individual elements of the system, the possibility of coincidence of these shutdowns, etc. The system must provide power to each consumer node with a total load above 10 MVA from two independent sources with automatic input of backup elements and switching power from one source to another. When choosing a power supply scheme, it is necessary to take into account the flexibility of the system, i.e. its adaptability to different modes of power distribution arising in the course of operation. Especially a sharp change in operating mode occurs when sudden disconnections of individual elements of the system due to emergency damage to various equipment, cables, etc. Should be considered the need to disable the system elements for repairs, tests, inspections and other operational needs. In determining principles of the power supply system of the city must strive to provide the demand for energy in ever-increasing sizes, keeping in mind the continuous increase in the load for a long time, without requiring any fundamental changes as its separate elements and system as a whole. At the same time, if the need arises due to an increase in the load after a long period of time or the emergence of new equipment with improved technical and economic performance, the system should be able to be converted to another power supply system. The design of the power supply system should be carried out with the identification of the priority of development for a period of not less than 10 years and the possibility of its subsequent expansion. An essential requirement is the need to maintain the short-circuit power within the limits permissible for the equipment used, at all stages of development of the system. The latter can be carried out by dividing the system into parts, separate operation of transformers, the use of reactors, etc. (depending on the stage of development of the system). At all design modes of operation of the system, the required quality of energy supplied to consumers must be ensured. The desired voltage level by the appropriate choice of parameters of separate elements of system and also through the use of special measures, such as installing a CPU of transformers with voltage regulation under load, the use of ‘condensing units industrial enterprises, not only for reactive power compensation but also for voltage regulation, etc. We emphasize the economic feasibility of the use of voltage regulation in the power supply system of the city, as in this case we are talking about the use of funds for a significant population of consumers. When selecting individual elements of the power supply system, it is necessary to strive for the implementation of joint power supply of different groups of consumers. According to the electrical safety rules, the issues of electricity supply to consumers should be solved comprehensively taking into account the state of energy of the area and the identification of all its consumers. In order to reduce the reserves in electrical networks, it is recommended to establish connections between the networks of different departments (industrial enterprises, municipal consumers, etc.) for mutual redundancy of loads.

4. Perfect power supply system of the city

These basic requirements for a rational power supply system of the city served as the basis for the development of an ideal system that would satisfy all the above conditions and was practically feasible. In relation to large and medium-sized cities, in particular, a power supply system based on the use of only two voltages: 110 and 10 kV can be considered [6].  The 110kV network is performed in the form of a ring covering the city. The schematic diagram of the ideal system is shown in Fig.3. The territory of the city to select the parameters of the main elements of the system is considered to consist of three parts: the central, with the highest load density, the middle part and the outskirts of the city, with the lowest load density. Fig.3. Perfect power supply system of the city   For the power supply of the central part of the city, the construction of a sufficiently powerful 110/10 kV substation is envisaged, which is powered by a 110 kV diametrical electrical connection passing through the city (Fig.3). The power sources located in the territory of the city and out of its limits, give energy directly in a ring of 110 kV which is as though collecting tires of all power sources of the city. By means of a ring their parallel work is carried out. At the same time, at the expense of urban substations 110/10 kV, located along the ring, in the load centers of individual districts of the city, energy is diverted to the distribution networks of 10 kV. The number of 110/10 kV ring substations is determined by local conditions, in particular, the optimal capacity of substations, or the load of large consumers. For creation of the most favorable conditions of distribution of energy in system and implementation of the most favorable modes of its work the corresponding alternation on length of a ring of 110 kV of connections of power supplies and lowering substations is recommended. The number of lines rings on kV, and also their constructive fulfilling is determined by local conditions. On the outskirts of the city, it can be in the form of overhead lines, which reduces the cost of the power supply system, the 110 kV diametrical connection is performed in all cases by cables. The total capacity of the ring 110 kV should be such that the power supply of the city is maintained under various emergency conditions: in case of damage and sudden failure of individual parts of the system. The operating mode of the 110 kV ring and the circuit of the ring substations, in addition, take into account the permissible conditions of short-circuit power in 10 kV distribution networks. The system in question will satisfy all the above conditions for a long period of time and, above all, the possibilities of its further expansion without radical breakage. At the same time, as the load of urban consumers increases and new facilities appear, the corresponding development of the system can be carried out in different ways. In particular, the capacity of the 110 kV network can practically be increased in any way by increasing the number of 110 kV lines, i.e. by repeatedly repeating the 110 kV ring. At the same time, new 110 kV lines can be laid on other routes of the city with the construction of 110/10 kV substations in load centers. At the same time, additional 110 kV diameter connections with new 110/10 kV substations, as well as deep kV input substations, may be envisaged. Depending on the load of the power supply system and local conditions, its power can be amplified by feeding power from the external power supply at a higher voltage, e.g. 380 kV. While at the nodal points of the separate ring parts 110 kV are connected so that the short-circuit power at each point of the 110 kV network were within the prescribed limits. In this regard, each ring 110 kV system under local conditions can operate independently of one another, and in this case there are as it were two independent power supply systems that communicate with each other only at a higher voltage of 380 kV. As the load of the city increases, the further development of its power supply system is carried out by creating a 380 kV ring network and increasing the number of 380/110 kV substations. With the development of the 380 kV network, the 110 kV ring network begins to lose its importance and is gradually transformed into a distribution network. Its development is limited. Increasing the capacity of the power supply system is made by opening the 110 kV ring network and winding its lines to new 380/110 kV substations. At the same time, the 110 kV network in the power supply system of the city begins to perform only the function of deep input. Thus, there is a natural process of introducing a higher voltage into the system, which is dictated by a continuous increase in the electrical load of the cities Conclusion   Due to the acceleration of scientific and technological progress, the consumption of electricity in industry has increased significantly due to the creation of flexible automated production facilities. In the near future, the energy sector faces the task of all-round development and use of renewable energy sources: solar, geothermal, wind, tidal, etc.; development of combined power generation and heat for district heating of industrial cities. The system of power supply of the city is understood as a set of electric networks and transformer substations located in the territory of the city and intended for power supply of its consumers. Power of urban consumers by means of distribution networks with voltage 6-10 kV and 0.38. The distribution network of 6-10 kV runs on a loop diagram; in normal mode, open loop. In defining rational ways of building a supply system sets out the General principles of its implementation, configuration of networks of accepted voltages, layout of substation and power sources, the order of construction of individual elements of the system, the choice of power supply (i.e. the definition of the necessary electrical connections between all elements of the system). The scheme of power supply of the city in the first place should be based on the established optimal parameters and voltage levels of individual elements of the system, as well as the number of energy transformations. It should be taken into account that the system is designed to supply energy to a very large number of consumers. Thus the choice of the scheme of power supply of the city is made irrespective of character of consumers and the required level of reliability of supply of their receivers of energy. The design of the power supply system should be carried out with the identification of the priority of development for a period of not less than 10 years and the possibility of its subsequent expansion. When selecting individual elements of the power supply system, it is necessary to strive for the implementation of joint power supply of different groups of consumers. References  

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