Exchange power supply to cities

Contents

Introduction

1 Plan and explication of the projected area

2 Brief description of the residential area

3 Calculation of electrical loads 0.4 kV of residential area

3.1 Calculation of electrical loads of domestic consumers

3.1.1 Calculation of electrical loads of residential buildings

3.1.2 Calculation of electrical loads of buildings with built-in enterprises

3.2 Calculation of electrical loads of public utilities

3.2.1 Calculation of electrical loads of public buildings and

constructions

3.2.2 Calculation of lighting load

3.3 Calculation of electrical loads of distribution network 0.4 kV

3.4 Selection of 0.4 kV distribution network diagram

3.5 Selection of sections of distribution network lines 0.4 kV

3.6 Calculation of 0.4 kV electrical loads on TC buses

4 Selection of TT number and power taking into account compensation

5 Selection of TC diagram and structure

6 Determination of power losses in transformers

7 Calculation of electrical loads on the 10 kV side

7.1 Calculation of electrical loads on the 10 kV side

7.2 Calculation of electrical loads of 10 kV distribution lines

7.3 Selection of Distribution Network Diagram

7.4 Selection of distribution network sections

7.5 Calculation of RP electrical loads

7.6 Check of KRM necessity on RP buses

8 Selection of 10 kV supply line circuit

9 Selection of 10 kV feed line sections

10 Selection of WP diagram and design

11 Calculation of short-circuit currents

11.1 Calculation of short-circuit currents in 10 kV network

11.2 Calculation of short-circuit currents in the 0.4 kV network

11.3 Results of short circuit currents calculation

12 Checking selected sections

12.1 Check of line sections for stress loss

12.2 Check of line sections for impact of short circuit currents 10.

13 Selection and inspection of electrical devices

13.1 Selection and check of switches on RP

13.2 Selection of fuses

13.3 Selection of load switches

13.4 Selection of circuit breakers

14 Calculation of capacitive ground fault currents and selection of DGR

15 Voltage control in urban electrical networks

16 Relay protection and automation

Conclusion

Bibliographic list

Appendix A Calculation of electrical loads

Appendix B Technical Calculation

Project Description

The course project contains 91 s., 13 figures, 11 tables, 11 sources used.

Cable line, transformer substation, explication, distribution substation, calculation of electrical loads, input switchgear, current, power, compensating devices, utility consumer.

Selection of the schematic diagram of electrical connections of the distribution network, development of the power supply system of the residential area, in particular, determination of the design load of 0.4 kV, calculation of the load of residential buildings, calculation of the load of utility consumers, calculation of the lighting load, selection of sections of cable lines, calculation of short-circuit currents, verification of switching protective equipment and selected sections.

Introduction

The city's power supply system means a set of electrical networks of all voltages located on the territory of the city and intended for power supply to its consumers. There are power supply networks with a voltage of 35-110, kV and above and distribution networks with a voltage of 0.4-10 kV. Given the continuous development of existing cities and the emergence of new ones, as well as the increasing amount of electric energy transmitted through urban power supply systems, a lot of attention is paid to the rational construction of such systems. The development of our country's economy is inextricably linked with the electrification of all sectors of the national economy. The gradual improvement of the well-being of citizens and the standard of living leads to an increase in the level of electricity consumption. In this regard, the course project was carried out in accordance with new technical standards and documents.

Efficient power supply is achieved by developing advanced power distribution systems, using rational designs of complete switchgears and transformer substations and developing optimization of the power supply system. Efficiency is affected by the selection of rational voltages, optimal values ​ ​ of sections of wires and cables, the number and power of transformer substations, means of compensation of reactive power and their placement in the network.

The implementation of these requirements ensures a reduction in costs during the construction and operation of all elements of the power supply system, increased reliability of the circuit and high-quality electricity supply to electricity consumers .

This course project considers the design of a residential area of ​ ​ the city of Blagoveshchensk, limited by Lenin - Amurskaya, Pushkin - Partizanskaya streets.

Brief description of the residential area

The residential district is located in the central part of the city and is bounded by Lenin, Amurskaya, Partizanskaya and Pushkin streets.

The city of Blagoveshchensk is the administrative center of the Amur Region, an important industrial, cultural and scientific center of the Far East.

The city is located in the south of the Amur Region, 600 kilometers west of the city of Khabarovsk, on the left bank of the Amur River. The area of ​ ​ urban land is about 321 square kilometers. The relief of the city is calm, fluctuations in elevation from 128 meters to 136 meters. The city is located in the I climatic region, in subdistrict 1A. Estimated climatic conditions correspond to the III region in wind and II in ice. The climate of the city of Blagoveshchensk is characterized by both the features of the continental climate and the monsoon, it is characterized by harsh, snowy winters and quite hot summers with heavy precipitation. The climate is characterized by sharp continental and uneven precipitation.

Main characteristics of climatic conditions in Blagoveshchensk:

- Ice area - 2;

- Normal wall of ice, mm - 10;

-Wind area - 2;

-The lowest air temperature is -45;

- Average annual air temperature - + 5;

- Higher air temperature - + 40;

- Number of thunderstorm hours per year - 34;

- Snow cover height, max/average, cm - 35/10;

-The degree of air pollution - 1;

- Ice temperature - -10;

The permanent population of the city of Blagoveshchensk is approximately 223.2 thousand people (22.7% of the population of the Amur Region). The population density of the city is 744 people per 1 square kilometer. Consequently, the city of Blagoveshchensk is one of the largest cities.

All consumers of the city, by the nature of electric consumption and indicators of electric load, are divided into the following groups:

1) consumers of residential areas;

2) industrial consumers;

3) municipal consumers of citywide importance (water supply, sewerage, electrified transport, etc.);

4) consumers of suburban areas.

Today, the city of Blagoveshchensk is the main industrial center of the region. 6.4 thousand enterprises and organizations were registered on its territory, including 705 engaged in the production of industrial products, 614 in construction, 2638 in trade and public catering, 97 in transport enterprises.

In the area of ​ ​ the city under consideration, the predominant part of the buildings is apartment buildings. However, there are also public service facilities, such as schools and kindergartens. There are office buildings, land plots for housing car parks and garages.

The territory of the settlement by purpose belongs to the settlement zone.

Calculation of electrical loads 0.4 sq of residential area

The first stage of designing power supply systems is the calculation of electrical loads. The calculated load is called the load by which electrical equipment, the power of power sources, the cross section of cables and wires, the power of transformers are determined and selected. A feature of calculation in urban systems is that data on the characteristics of electric receivers may not be known, and it is almost impossible to take into account them, so they use various methods to determine loads. They use methods of calculating electrical loads on the specific consumption of electricity, per unit of production, on the specific load per unit of area or one visitor, the number of places. The determination of the calculated capacity of loads should be made using any of the existing methods of calculating them. We will calculate using the method of specific electrical loads.

Calculation of electrical loads on the 10 sq side

7.1 Calculation of electrical loads on the 10 kV side

To calculate the electric load on the 10 kV side, it is necessary to take the power reduced to the 10 kV side, i.e. taking into account the losses in transformers that were calculated in the previous paragraph. The calculation was performed in Mathcad 14 and is presented in Appendix B. The calculation was discussed in the previous paragraph and the calculation data are given in Table 8, together with the losses.

Calculation of short-circuit currents

Short circuits are faults between phases, phase faults to ground (zero wire) in networks with blind and effectively grounded neutrals, as well as winding faults in electrical machines. Short circuits occur when the insulation of electrical circuits is broken. Most often, DC occurs through a transient resistance, for example, through the resistance of an electric arc that occurs at the point of insulation damage. Sometimes, a metal short-circuit occurs without transient resistance. To simplify the analysis, in most cases, when calculating short circuit currents, a metal short circuit is considered without taking into account transient resistances.

With a three-phase short circuit, all phases of the electric network are in the same conditions, so it is called symmetrical. In other types of SC, the phases of the network are in different conditions, in connection with which the vector diagrams of currents and voltages are distorted. Such KZs are called asymmetric.

The flow of DC currents leads to an increase in power losses in conductors and contacts, which causes their increased heating. Heating can accelerate the aging and destruction of insulation, cause welding and burnout of contacts, loss of mechanical strength of tires and wires, etc .

Conductors and devices shall tolerate without damage during the specified design time heating by short circuit currents, i.e. they shall be thermally resistant.

Calculation of short circuit currents is performed for selection or check of electrical equipment parameters, as well as for selection or check of relay protection and automation settings.

When calculating short circuits, the following assumptions are taken into account: it is assumed that the EMF phases of all generators do not change (absence of oscillation of generators) during the entire short circuit process, saturation of magnetic systems is not taken into account, which makes it possible to consider the inductive resistances of all elements of the short circuit that are constant and independent of current, neglect magnetizing currents of power transformers, do not take into account, except for special cases, capacitive conductivities of elements of the short circuit to the ground, consider that the three-phase system is symmetrical, the effect of load on Q3 current.

Selection of load switches

Load switches in combination with a high-voltage fuse replace the switch. Load switches are performed at rated currents 200 and 400 A. Selection of load switches is performed at rated operating voltage and current.

We accept to installation on all TP switches of loading of BHP10 400 type with the PR 17 drive, the amplitude value of limit current is 41 kA, therefore the chosen switches will approach on thermal firmness.

Voltage regulation in urban electrical networks

Voltage control is an automatic or manual deliberate change in the voltage mode of the electrical network in order to ensure the required level of electricity quality and cost-effectiveness of the network. The mode is changed by one-time measures that affect the voltage value. The magnitude of the voltage can be changed by changing the voltage of the generators or using transformers, using VRP devices. Synchronous compensators or static capacitors can be installed on substations. The CPU can use voltadditioning devices. These control methods result in a change in the voltage of all connections. Transformers with RTD device shall be installed on all substations supplying the distribution network. Linear regulators can be installed on substations with transformers without RTD. If the centralized control does not provide the required quality of electricity, then local voltage control means are used. Consumers can have capacitor batteries, or synchronous motors. In addition to the above means, branches are used on the high voltage side of the step-down transformers, which are switched without excitation, by PBV devices.

Relay protection and automation

Normal operation of any electrical equipment can be interrupted by any disturbances and emergency situations. In particular, for a transformer, these are:

- multiphase circuits in windings and on leads;

- single-phase faults in windings (including winding) and on leads;

- external short circuits;

- winding overload;

oil ignition;

lowering of oil level;

Protection against any specified damages, including winding coils, is longitudinal differential current protection.

Gas protection is used to protect against faults inside the tank, accompanied by gas release.

Longitudinal differential current protection, acting without delay to disconnect the damaged transformer from the intact part of the electrical system and other electrical installations using switches. Such protection is performed on transformers with a capacity of 6.3 MV· A and more, as well as on transformers with a nominal power of 4MV· A, if they work in parallel on lower voltage buses (in order to selectively disconnect the damaged transformer).

Current transformers for longitudinal differential current protection are installed on all sides of the protected transformer. For double-winding transformers having a Y/Δ winding connection circuit, the secondary windings of current transformers on the high voltage side are usually connected to a triangle, and on the lower voltage side to an incomplete star, while two relays are installed in the differential circuit.

Longitudinal differential current protection is carried out with the use of current relays, which have improved adjustment from magnetizing current surges, transient and steady currents of non-balance. It is recommended to use relays with DST - 11 type braking or DST - 21 protection kit.

The differential protection of the transformer with the DST-11 relay is performed so that in case of internal damage to the transformer, braking is minimal or minimal or completely absent. Therefore, the brake winding is usually connected to current transformers installed on the lower voltage side of the transformer.

The sensitivity of the differential protection is checked at short circuit at the terminals taking into account the influence of an current flowing in the voltage control relay (RLP) during the operation of the automatic transformation coefficient control device.

Protection acts to disconnect the damaged transformer. When the make-up of damage in the twin-winding transformer from the lower voltage side is excluded, as well as when the LV-side switch is removed from the protection place by so much that the laying of the transmission cable of the signal disconnecting this switch is economically impractical, the protection action on disconnecting the switch only from the supply side is allowed.

Conclusion

Course design in the discipline of power supply to cities is one of the last in the course of students. The course project is designed to consolidate the knowledge gained during training, as well as to develop an engineering approach to solving complex design problems. The experience gained will be indispensable at the state exam in the discipline of the same name, as well as at the diploma design.

The design and validation of the distribution network provides an opportunity to understand the challenges faced by engineers in the design organizations, as well as some aspects of the actual application of such schemes by operational engineers. The main criterion for the design was the technical applicability and cost-effectiveness of the project.

This course project allows you to consolidate knowledge of the discipline "Power Supply to Cities," as well as acquire skills in the design of urban networks and low-voltage electric networks.