A power cable is a cable for transmitting electricity by currents of industrial frequencies.
In a practical sense, it means a cable for the transmission of three-phase current from the main switchboard of the input-distribution device of industrial enterprises, utilities and other facilities to consumers of electricity. Used for stationary installation, also used to connect mobile installations / units / equipment. Simply put, a power cable is a cable that is used to transmit electric current, which is already industrial, that is, high voltage. With the help of a power cable, it is possible to transfer electricity from substations to residential buildings, to industrial enterprises and public buildings. Mostly designed for voltages up to 10-35 kV, but there are brands that can withstand voltages up to 220 and 330 kV
Depending on the area and type of application, it can consist of various structural elements.
Each power cable consists of at least three elements:
To improve performance in a power cable, manufacturers may include:
cushions for armor;
The conductor material is usually copper or aluminum. The conductor insulation can be made of impregnated paper (paper-insulated cable) or polymer (eg XLPE).
The power cable with impregnated paper insulation is used in electrical networks with a voltage from 1 to 750 kV and a frequency of 50 Hz.
XLPE insulated cable is used at both low and high voltages, withstands high temperatures, has high strength, helps to avoid short circuits when the network is overloaded, and is lighter than other cables.
operating temperature: −50 … + 50 ° C;
temperature permissible for long-term heating of conductors: +90 ° C;
temperature, maximum allowable at short circuit: from +250 ° C;
service life: at least 30 years.
And now in more detail about the composition of the cables. Each power cable is made of a conductive core, insulation and sheath. Many power cables also have armor and shielding. Now in order.
What is a vein?
A core is one part of a cable that conducts electrical current. The collection of insulated conductors forms a core. The core is single-wire and multi-wire. The relative position or sectional shape of an element is flat and sectorial. Also, the cross-sectional area of the core is one of the important parameters.
There are conductive and grounding conductors.
The conductor is the core of the cable. The core can be made from 1-5 wires. The shape of the core elements can be round or segmented (sectorial). A round conductor has a circular cross-sectional surface. A sector (segment) vein has a shape similar to a triangle with rounded corners. Cable products are ordered by section type and diameter.
The neutral (ground) conductor is the conductor that connects the current source to the grounded or ungrounded neutral of the current source. This neutral ground the current. So that, if, when an extraneous current appears, these currents go into the ground. Without damaging the insulation of wires or cables. When several cables are laid side by side, inductive voltage appears between them. This voltage will damage the insulation over time. To prevent this from happening, there is a grounding conductor. Such conductors are used for uneven loads on the power grid. The grounding strands are centered on the wire and have a small cross-section. Their elements ensure the safe use of the cable.
Single-core and multi-core power cables and wires.
The wires in a power cable are divided into single-core (single-wire) stranded (multi-wire).
Solid wires are made up of one conductor. Products made from such wires are used to supply electricity to homes and public buildings. In industrial production, single-core wires are used to bring electricity from generators to the mains.
Stranded wires are made from several overpaid conductors. To increase plasticity, a thread is drawn between the cores in the middle of the wire. With the help of vibration-resistant flexible stranded wire products, household appliances can be connected to the mains.
What is a power cable and what is it made of?
What is the core of the power cable made of?
Different materials are used to create veins. Basically, these are alloys of aluminum, copper and steel. You can combine the compositions of raw materials. Synthetic materials are also acceptable. The wires are made of plastic or glass to transmit optical signals. Nichrome veins are used to dissipate heat.
In accordance with the production method, copper conductors are ductile or solid. The diameter of single-wire conductors is 16-95 mm, for multi-wire ones – 25-800 mm. Effective, reliable and durable copper alloys are expensive.
Aluminum conductors have little ability to conduct electricity. Elastic aluminum wires can deform, so they should be checked regularly for the safety of network connections. Aluminum alloy wires are solid.
Power cable shields, fillers and sheaths.
In the drain cable, there are absolutely necessary layers between the insulation. These are screens, fillers, casings and protective coatings.
Screen is a cable braid designed to reduce the influence of external electromagnetic radiation on the internal signal wire of the cable, and to reduce the parasitic radiation of signals passed through the internal conductors. Screens protect from external electromagnetic influences. They are made of foil, paper that has been treated with a special compound.
A filler is an element used to fill free gaps in a cable or wire in order to provide the required mechanical stability, longitudinal tightness and shape. Fillers made of plastic, rubber and paper tape come in the form of bundles. With the help of elements, you can change the density of the abutment of parts of all structures. The compositions give the product the desired shape, make the product airtight and resistant to external mechanical stress.
A pillow, armor cover, or armor is the last of the pieces of wire. The armor is made of galvanized strips and wires. It makes the product durable.
The sheath of the power cable must not conduct electricity.
If the DC voltage of the power grid is 10 kV, then cables with external rubber insulation can be used. Such products are used on routes with different levels of wiring. These plastic cable products are hygroscopic. Reserving the steel wire will stop deformation.
To make electrical wiring, which has a constant voltage of 0.66-6 kV, cables with PVC insulation are used. These inexpensive and flexible materials can be used in very cold and hot weather.
The lightweight, durable cross-linked polyethylene compound is highly resistant to moisture and temperature fluctuations.
So let’s take a look at the types of power cables.
Power cables with impregnated paper insulation in lead or aluminum sheath
Power cables with impregnated paper insulation with copper and aluminum conductors are intended for the transmission and distribution of electrical energy at a rated voltage of up to 10 kV inclusive. Such cables are used for fixed installation and depend on the difference in the level of the route. In order to protect the hygroscopic paper insulation, a lead or aluminum sheath is provided in the cable construction. Cables with aluminum sheaths must not be used in conditions of exposure to aggressive media (alkali vapors, concentrated alkaline solutions). In such conditions, it is necessary to use cables with lead sheaths.
Power cables with rubber insulation
They are used for stationary installation in power grids up to 10 kV DC. The cables are designed for laying on routes with unlimited level differences. Advantages of rubber-insulated cables: low hygroscopicity (moisture absorption) and flexibility. However, rubber is not resistant to ultraviolet light and ozone, so the cable has steel armor that protects the cable from destructive factors.
Power cables with PVC insulation
Power cables with PVC insulation are designed for stationary installation in power grids with a rated alternating voltage of 0.66 kV, 1-6 kV. PVC-based insulation is one of the cheapest cable insulations with elasticity, and thanks to special additives, it can acquire the necessary properties, for example, frost resistance and heat resistance.
Power cables with polyethylene insulation
Power cables with XLPE insulation appeared in the 70s of the 20th century. The new XLPE insulated cable is intended to replace obsolete cables with impregnated paper insulation. The cables are designed for voltages of 6, 10, 15, 20, 30 and 35 kV (first group); 45, 60, 110, 132 and 150 kV (second group); 220 and 330 kV (third group); the cross-sectional area of cables varies from 35 to 200, there are cable products with a larger cross-section -1000 and more mm2. Compared to paper insulation, XLPE cables withstand higher core temperatures, are moisture resistant, and are lighter in weight.
Types of power cables:
AVVG – Power cable with aluminum conductive core, insulation and sheath made of polyvinyl chloride (PVC) plastic compound, without protective cover.
VVG – Power cable with copper conductor, PVC insulation and sheath, without protective sheath. Additional marking of the form (4 × 4) means that the cable is four-core (first number) with a cross-section of 4 mm (second number).
AVVG-P – Power cable with aluminum conductive core, insulation and sheath made of polyvinyl chloride (PVC) plastic compound, without protective cover, flat.
VVG-P – Power cable with copper conductor, PVC insulation and sheath, without protective sheath, flat.
AVVGng – Power cable with aluminum conductive core, PVC-compound insulation, low-flammability PVC-compound sheath.
VVGng – Power cable with copper conductive core, PVC-compound insulation, low-flammability PVC-compound sheath.
AVVG-Png – Power cable with aluminum conductive core, PVC insulation, low flammability PVC sheath, flat.
VVG-Png – Power cable with copper conductor, PVC-compound insulation, low-flammability PVC-compound sheath, flat.
AVVGng-LS – Power cable with aluminum conductive core, insulation and sheath made of PVC compound with low fire hazard. Low Smoke, low smoke and gas emission.
VVGng-LS – Power cable with copper conductive core, insulation and sheath made of PVC compound with low fire hazard. Low Smoke, low smoke and gas emission.
AVBbSHv – Power cable with aluminum conductive core, PVC-compound insulation, armored (armor made of two galvanized steel strips; PVC-compound protective hose).
Designed for stationary operation at ambient temperatures from plus 50 ° C to minus 50 ° C, relative air humidity up to 98% at temperatures up to 35 ° C, including for laying in the open air. The duration of operation of this cable in emergency mode should not be more than 8 hours a day and not more than 1000 hours during its service life.
VBbSHv – Power cable with copper conductive core, PVC-compound insulation, armored (armor made of two galvanized steel strips; PVC-compound protective hose). For laying in the ground (trenches), rooms, tunnels, canals, mines (except for laying in blocks), as well as in the open air, if the cable is not subjected to significant tensile forces, if there is a risk of mechanical damage during operation.
AVBbSHvng – Power cable with aluminum conductive core, PVC-compound insulation, armored (armor made of two galvanized steel strips; protective hose made of PVC-compound of low flammability).
VBbSHvng – Power cable with copper conductive core, insulation made of (PVC) plastic compound, armored (armor made of two galvanized steel strips; protective hose made of PVC compound with low flammability.
VBbSHvng-LS – Power cable with copper conductive core, insulation made of PVC compound of low fire hazard, armored (armor made of two galvanized steel strips; protective hose made of PVC compound of low fire hazard).
The service life of the power cable.
The durability of the cables is indicated by national regulations. It is divided into actual, that is, real and warranty.
The manufacturer issues a guarantee for its product for a period from the start of using the product.
Expiration date of the cable – the actual time of use of the product according to standard technical characteristics. For cables with plastic insulation, the actual duration and time of use is approximately 25 years. Paper impregnated wires can be used for 30 years.
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