Design of electrical networks 0.38 and 10 kV in rural areas

When designing electrical networks, the following types of work are taken into account: new construction, expansion and reconstruction.

New construction includes the construction of new transmission lines and substations.

Expansion of electrical networks, as a rule, applies only to substations — it is the installation of a second transformer at an existing substation with the necessary construction works.

The reconstruction of existing networks implies changing the parameters of the power transmission networks, while partially or completely preserving the construction part of the facilities, in order to increase the transmission power of the networks, the reliability of the power supply and the quality of the transmitted electricity. Reconstruction includes work on replacing wires of overhead lines, transferring networks to a different nominal voltage, replacing transformers, switches and other equipment in connection with a change in power or voltage, installing automation equipment in networks.

The system for supplying agricultural consumers is designed taking into account the development of all sectors of the national economy in the region under consideration, including non-agricultural ones.

Design and accounting documentation is developed based on a design assignment. The assignment, as noted above, is issued by the project client and approved for the power grid construction sites in accordance with the established procedure.

The client of the project, in addition to the design assignment, issues to the design organization an approved document for the selection of a construction site; an act of assessment of the technical condition of the operating electrical networks; technical conditions for connecting to engineering networks and communications; cartographic materials; information about existing buildings, underground utilities, the state of the environment, etc.; technical conditions for connecting the designed facility to power sources.

The assignment for the design of 10 kV overhead lines is additionally attached: land use plans in the area of ​​the power line; general plans of the designed objects that will be connected to the designed lines and their loads; an act of assessment of the technical condition and schemes of working electrical networks in the area of ​​the designed line; topographic maps of settlements in the area of ​​the designed line, as well as other design data.

The assignment for the design of 0.38 kV lines and 10 / 0.4 kV transformer substations includes: basis for design; construction zone; Type of construction; line length 0.38 kV; type of transformer substations; scenic design; the duration of the project; construction start date; the name of the design and construction organizations; capital investment. In addition, the assignment for the design of 0.38 kV networks is accompanied by: technical specifications of the electrical power system for connection to electrical networks; act for assessment of the technical condition of 0.38 kV networks; data on the achieved level of electricity consumption for a residential building and other materials.

The design of construction sites is carried out on the basis of schemes for the development of electrical networks of 35 ... 110 kV and 10 kV, as a rule, in one stage, i.e. develop a project for technical design — technical project and working documentation for the construction of the facility.

When designing the construction of new, expansion, reconstruction and technical re-equipment of existing electrical networks with a voltage of 0.38 ... 110 kV for agricultural purposes, they are guided by the "Technological design standards for electrical networks for agricultural purposes" (STPS) together with others regulatory and directive documents. The requirements of the Norms do not apply to electrical power supply wiring, lighting circuits with a voltage of up to 1000 V inside buildings and facilities.

Power lines 0.38 … 10 kV, as a rule, must be carried out above ground. Cable lines are used in cases where according to PUE the construction of overhead lines is not permissible for the supply of responsible consumers (at least one of the main or backup power lines) and consumers located in areas with severe climatic conditions (IV — special ice zone) and valuable lands.

Transformer substations with a voltage of 10 / 0.4 kV are used of closed type and full factory production.

The justification of technical solutions is carried out on the basis of technical and economic calculations. Among technically comparable options, preference is given to the option with the lowest reduced costs.

Schematic solutions of electrical networks are selected according to normal, repair and post-emergency modes.

The distribution of voltage losses between the elements of the electrical network is carried out on the basis of a calculation based on the permissible voltage deviation (GOST 13109-97 — the permissible normal voltage deviation for the user is ± 5% of the nominal, the maximum deviation is allowed up to ± 10 %) for power consumers and voltage levels in the bus center feed.

Loss of voltage should not exceed 10 kV in electrical networks — 10%, in electrical networks 0.38 / 0.22 kV — 8%, in electrical wiring of one-story residential buildings — 1%, in electrical wiring of buildings, structures, two-story and multi-story residential buildings — 2%...

In the absence of initial data for calculating the voltage deviation for electrical receivers, it is recommended to take voltage losses in the network elements of 0.38 kV: in the lines supplying utility users — 8%, industrial — 6.5% , livestock complexes — 4% of the nominal value.

In the design of electrical networks for agricultural purposes, the power of compensating devices must be determined according to the condition of providing an optimal reactive power coefficient, in which a minimum of the reduced costs of reducing electricity losses is achieved.

Design requirements for power lines with a voltage of 0.38 / 0.22 kV

When designing overhead lines with joint suspension on wire supports of power lines 0.38 / 0.22 kV and cable lines with a voltage of up to 360 V, it is necessary to be guided by PUE, the use of overhead line supports for joint suspension of supply wires (380 V) and cable radiation (not higher than 360 V) and NTPS.

On the sections of parallel following lines of 0.38 and 10 kV, the technical and economic possibility of using common supports for joint suspension of wires of the two overhead lines on them should be taken into account.

The selection of wires and cables, the power of power transformers must be carried out at a minimum of the given costs.

Power lines with a voltage of 0.38 kV must have a solidly grounded neutral; on lines extending from one 10 / 0.4 kV substation, no more than two or three wire sections should be provided.

Selected wires and cables are checked:

• about permissible deviations of voltage at consumers;

• for permissible long-term current loads according to heating conditions in normal and after emergency modes;

• to ensure reliable operation of the protection in case of single-phase and phase-phase short circuit;

• for starting squirrel-cage rotor induction motors.

Plastic-insulated cables protected by fuses must be tested for thermal resistance against short-circuit currents.

The conductivity of the neutral wire of 0.38 kV lines supplying mainly single-phase loads (more than 50% in terms of power), as well as electrical receivers of livestock and poultry farms, must be not less than the conductivity of the phase wire. The conductivity of the neutral conductor may be greater than the conductivity of the phase conductor if this is necessary to ensure the permissible voltage deviations for lamps for outdoor lighting, as well as when it is impossible to provide other means of the necessary selectivity for line protection from single-phase short circuits. In all other cases, the conductivity of the neutral conductor must be taken at least 50% of the conductivity of the phase conductors.

On overhead lines to individual consumers with a concentrated load, it is necessary to provide for the suspension of eight conductors with the division of the conductor from one phase to two on supports with a common neutral conductor. In the case of joint suspension of common supports of wires from two lines connected to independent power sources, it is necessary to provide independent neutral conductors for each line.

Street lighting conductors must be located on the side of the street lane. The phase wires must be located above zero

Street lighting fixtures are connected to specially designed phase conductors and a common neutral conductor of the electrical network. Luminaires are placed in a checkerboard pattern when installed on both sides of the street.The switching on and off of the street lights must be automatic and done centrally from the switchboard of the transformer substation. VL 0.38 kV are equipped with aluminum, steel-aluminum conductors, as well as aluminum alloy.

In areas with single-story buildings, it is recommended that self-supporting conductors with weatherproof insulation be used for branching from lines to building entrances.

The selection of 10 kV overhead line routes must be carried out in accordance with the requirements of the regulatory documents for the selection and survey of line routes.

If it is necessary to build overhead power lines that run in the same direction as the existing ones, technical and economic calculations should be carried out to justify the possibility of building new ones or increasing the capacity of existing lines.

The nominal phase-phase voltage of distribution networks above 1000 V should be taken at least 10 kV.

When reconstructing and expanding existing networks with a voltage of 6 kV, it is necessary to provide for their transfer to a voltage of 10 kV, using, if possible, installed equipment, wires and cables. Maintaining a voltage of 6 kV is exceptionally permitted with appropriate feasibility studies.

On 10 kV overhead lines with pin insulators, the distance between anchor supports should be no more than 2.5 km in I -II areas on ice and 1.5 km in III — special areas.

On 10 kV overhead lines, the use of steel-aluminum conductors is recommended, in areas with a standard ice wall thickness of 5-10 mm and a high-speed wind pressure of 50 N / m2, the use of aluminum conductors is allowed.

Cable lines are recommended to be made with a cable with aluminum conductors with plastic insulation.

Overhead can be built using reinforced concrete on vibrated and centrifugal racks, wooden and metal supports.

Steel supports of 10 kV overhead lines are recommended to be used at intersections with engineering structures (railways and highways), with water spaces, on limited sections of routes, in mountainous areas, on valuable agricultural land, and also as anchor-corner supports on double contour lines.

It is recommended to use double-circuit supports on 10 kV overhead lines at large crossings over water obstacles, as well as on sections of overhead lines passing through lands occupied by agricultural crops (rice, cotton, etc.), as well as at the approaches to substations , if construction is planned in this direction. one line.

10 kV overhead lines are performed using pin and suspension insulators, both glass and porcelain, but glass insulators should be preferred. Suspended insulators must be used on 10 kV overhead power lines for livestock farms and on anchor supports (end, anchor corner and transition supports).

Design requirements for 10 kV transformer substations

Substations 10 / 0.4 kV must be located: in the center of electrical loads; adjacent to the access road, taking into account the provision of convenient approaches to overhead and cable lines; in unheated places and, as a rule, in places with a level of groundwater below the foundations.

Power supply domestic and industrial users are recommended to be supplied from different substations or their sections.

It is not recommended to place substations with air ducts near schools, children's and sports facilities.

Schemes of substations are selected on the basis of schemes for the development of electrical networks in areas of 35 ... 110 kV and technical and economic calculations for the expansion, reconstruction and technical re-equipment of electrical networks with a voltage of 10 kV in areas of electrical networks and are indicated in the working projects to power real facilities.

The choice of schemes for connecting 10 / 0.4 kV substations to power sources is based on an economic comparison of options depending on categories of electricity consumers in terms of power supply reliability in accordance with the "Methodological guidelines for ensuring the design of the standard levels of reliability of the supply of agricultural consumers"

Substations 10 / 0.4 kV, supplying users of the second category with an estimated load of 120 kW and more, must have bidirectional power supply. It is allowed to connect a 10 / 0.4 kV substation, supplying consumers of the second category with a design load of less than 120 kW, with a branch of a 10 kV highway, separated at the point of the branch on both sides by disconnectors, if the branch length does not exceed 0.5 km.

10 / 0.4 kV substations, as a rule, should be designed as single transformers. Two-transformer substations 10 / 0.4 kV must be designed to supply consumers of the first category and consumers of the second category, which do not allow interruption of the power supply for more than 0.5 hours, as well as consumers of the second category with an approximate load of 250 kW or more.

It is recommended to equip two transformer substations with devices for automatically switching on the backup power supply of 10 kV busbars under a combination of the following mandatory conditions: the presence of energy consumers of I and II categories; connection to two independent power supplies; if simultaneously with the tripping of one of the two 10 kV supply lines, a power transformer simultaneously loses its supply. At the same time, consumers of electrical energy of category I must additionally be provided with automatic backup devices directly at the input of 0.38 kV of electrical consumers.

Closed type 10 / 0.4 kV substations must be used: when building supporting transformer substations, to 10 kV switchgears from which more than two 10 kV lines are connected; for powering consumers of consumers of the first category with a total design load of 200 kW and more; in the conditions of narrow development of settlements; in regions with a cold climate at an air temperature below 40 ° C; in areas with a polluted atmosphere of III degree and higher; in areas with a snow cover of more than 2 m. As a rule, 10 / 0.4 kV substations with air inlets from 10 kV lines should be used. Cable line seals must be used: in cable networks; during the construction of substations with only cable entries for lines; under conditions when the passage of overhead lines at the approaches to the substation is impossible and in other cases when this is technically and economically justified.

10 / 0.4 kV transformers are usually used with an OFF-tap for voltage regulation.

10 / 0.4 kV transformers with a capacity of up to 160 kVA inclusive with a "star-zigzag" winding circuit with a 0.4 kV neutral winding should be used for powering domestic agricultural consumers.

Rastorguev V.M.