The power cable allows you to transfer electricity from substations to household, industrial, public facilities. The wire structure consists of cores, insulating coatings, outer sheath, armor, screen. Products are divided into classes according to the type of alloy, structure and structure, the number of cores, the intensity of the passing voltage, etc.
Content
Product varieties
The purpose of power wires is to transmit electricity to residential buildings, public organizations, and industries. Products are classified according to the parameters and characteristics of cables, internal wires, sheaths, etc.
External (external) protection against atmospheric precipitation and changing weather conditions in cables for electrical wiring can be armored or unarmoured. The control cable differs from the power wire in less strength, because. has no reinforcement.
According to the constructive solution of the current-carrying cores, the products are divided into single-core cables or with 2-5 wires (multi-core).
The voltage classification divides cables into those intended for operation under pressure:
- low;
- average;
- high.
Products differ in the total mass and weight of individual elements (insulation, cores, screens).
Popular and popular power cable designs include the following types:
- PPV;
- APPV;
- VVG;
- PVA;
- VBbShv;
- NUM;
- KG.
The PPV cable consists of a copper core (three-core) protected by a layer of polyvinyl chloride. The products are used for indoor lighting. Products must be fixed statically.
APPV wire is made mainly from aluminum alloys; material travels along the length of the wire.
The core of the VVG cable consists of copper, has 1-4 cores. The protective cover is made of PVC. Cables are used for conducting lighting lines in residential and public complexes with different temperatures and air humidity.
Copper in the composition of the PVA wire ensures the plasticity of the structure. In accordance with the thickness of the product, 2-5 twists of the parts of the rod are allowed. Wires are used in household appliances, lighting systems, adapters.
In VBbShv cables, up to 5 twists of cores are provided. Products are used in the construction of power lines. The products are strong and durable.
The NUM wire has an outer sheath made of non-combustible material, 2-4 inner cores.Wires are optimal for electrical wiring. The advantage of products lies in the resistance to deformation; the design withstands temperature fluctuations from -50 to +50°C.
As part of the cable brand KG - stranded conductors of copper. The protective layer consists of a rubberized insulator. Strength, ductility, moisture resistance of products allow the use of products in difficult areas.
The concept of core in electrical wiring
The device of power cables includes plastic conductors made of metal alloys. The core can be single-wire or multi-wire. The configuration of the section of the element is different (flat, sector). An important characteristic is the cross-sectional area of \u200b\u200bthe core.
Conductive and neutral ground conductors
The cores, in accordance with the purpose, can be conductive or grounding (zero).
Conductor is the main element in the cable. The core may contain 1-5 wires. The shape of the elements according to the standards is round, segmental or sector type. Products are standardized according to the type of section and diameter.
Zero cores are used for uneven loads on the power grid. Grounding threads have a small cross section and are placed in the center of the wire. Elements ensure safe operation.
core insulation
The cores in the wires must be insulated with a special coating.
As protective raw materials are used:
- paper;
- rubber;
- plastic.
Paper insulation involves applying layers to the cores and impregnating the raw material with a fire-resistant composition. Products are used on equipment operating under high voltage.
The insulating rubber coating is plastic, strong, durable.Rubber-sheathed cores are used in cables for connection to devices that are moved during operation. It is necessary to take into account the sensitivity of rubber to sub-zero temperatures. To prevent deformation, the cores are supplemented with a polyvinyl chloride coating.
An insulating layer made of plastic (polyethylene or polyvinyl chloride) is budgetary, reliable, has high insulation, and a long shelf life.
Single and stranded
The design of the power cable includes wires:
- single-core;
- stranded.
Single-core wire includes 1 current conductor. Products are used in public buildings, residential complexes for supplying electricity. In industrial premises, single-core wires are used to output electricity from generators to the general network.
Stranded wires consist of several interlaced strands. To increase plasticity, a thread is pulled between the cores. Products are resistant to vibrations, flexible, designed to connect household appliances.
Core material
For the manufacture of cores, different types of raw materials are used (alloys of aluminum, copper, steel). Combined compositions and synthetic core materials are acceptable. To transmit optical signals, the wires are made of plastic or glass. Nichrome conductors are used to dissipate thermal energy.
Copper
Conductors made of copper in accordance with the manufacturing technology are made ductile or rigid. The diameter of single-wire elements is 16-95 mm², stranded - 25-800 mm². Cores with a rigid structure have a round cross section. Copper alloys are efficient, reliable, durable, but are expensive.
Aluminum
Aluminum conductors have a large cross-sectional area, are characterized by low electrical conductivity. The wires are soft, subject to deformation, oxidation, and require regular checks of the reliability of the connections in the electrical network. Aluminum alloy conductors have a rigid structure. The cross section of the wires must not exceed 1 mm². At residential facilities, aluminum conductors must have a cross-sectional area of at least 16 mm².
Screens, Placeholders, and Shells
The design of the power cable includes mandatory layers between the insulation:
- screens;
- placeholders;
- shells;
- protective coatings.
Screens are designed to protect the outer layers from electromagnetic influence. Elements are made of foil, paper treated with a special composition.
Fillers are made in the form of bundles of plastic, rubber, paper tapes. Elements allow you to adjust the density of adjoining parts of the structure. The compositions make the product hermetic, resistant to mechanical stress, give it the necessary shape.
Sheaths are designed to protect wire surfaces. Parts of the structure are made of aluminum alloys, lead, non-combustible plastics and rubber. Surfaces can be smooth or corrugated. Sheaths prevent wire deformation from the action of water, acid-base compounds.
The final in the design are protective covers (cushion, armored cover). Armor made of galvanized tapes and wires gives the product strength.
Wiring insulation
The sheath of the power cable is designed to isolate products from the external elements of the building. The coating must not conduct current.
The main types of cable insulation are represented by coatings:
- impregnated paper;
- made of durable rubber;
- from polyvinyl chloride;
- from polyethylene.
Polystyrene, fluoroplast, magnesium oxide, etc. can be used as insulation.
The designs of cables covered with paper sheets with a sheath of aluminum and lead are optimal for passing electrical energy with a voltage of 35 kV (GOST 18410-73). Aluminum coated insulation materials are not recommended for production sites using alkaline solutions. Lead-coated insulation protects against aggressive alkaline environments.
Cables with external rubber insulation are suitable for installation of electrical networks with direct voltage up to 10 kV. Wires are used in routes with different levels of electrical wiring (GOST 433-73). Products differ in high hygroscopicity, plasticity. The wire structure is equipped with a strong steel armor that prevents deformation.
Cables with PVC insulation are designed for electrical wiring with a rated voltage of 0.66-6 kV (GOST 16442-80). Materials are budget, plastic. When using additives, the composition becomes resistant to negative or elevated temperatures.
The outer insulating sheath made of cross-linked polyethylene (XPE) is an advanced composition, characterized by low weight, durability, resistance to moisture, and heat resistance.
Polyethylene is designed according to density for tension:
- 1 group (6-35 kV);
- 2 groups (45-150 kV);
- 3 groups (220-330 kV).
By shape
The configuration of the cable section in the section can be:
- sector;
- rounded uncompacted;
- round compacted;
- segment, etc.
The flat power cable is designed for industrial premises with dry and humid air, outdoor structures, overpasses. Products with a round section are designed for stationary electrical installations inside buildings.
Life time
The service life of the cable is regulated by state standards (GOST 16442-80, GOST 18410-73, etc.), divided into actual and warranty.
The warranty for the product is issued by the manufacturer for a period calculated from the beginning of the use of the structure. The procedure is valid if the buyer observes the rules of transportation, installation, operation. Plastic insulated wires are guaranteed for at least 5 years. Paper-insulated cables are warranted up to 4.5 years.
The service life of the cable represents the actual period of use of the structure up to the technical parameters allowed by the standard. The actual duration and period of operation for cables with plastic insulation is about 25 years. Wires insulated with impregnated paper can last up to 30 years.
Marking as a means of determining the type of cable
Features of the application and the composition of the wires are reflected in the marking code.
The standards adopted the marking of cables using different shades of insulation and wire busbars:
- brown and black colors indicate the core of the phase;
- neutral wires are fixed in a blue tint;
- ground conductors are indicated by a yellowish-green tone, etc.
Marking with an alphabetic code (PPV, APPV, VVG) is provided, which is applied to the label or product and fixes what the product consists of.
The following symbols indicate the types of insulation of power cables:
- P (polyethylene);
- H (non-combustible rubber);
- B (polyvinyl chloride);
- R (rubber), etc.
The rules for marking are fixed in GOST 18620-86.
In conclusion, I will add that power cables are transported wound on special wooden or plastic drums, as well as wound in coils.
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