Electrical networks (ES), built on open terrain, often serve as overhead lines (OHL). The length of the span of the overhead line differs from the installation of cable power lines – this is the distance between the centers of two adjacent supports on the ground.
Overhead cable lines: advantages and disadvantages
“A cable line is a line for the transmission of electricity, consisting of one or several parallel cables with connecting, locking and terminating couplings (terminations) and fasteners. The main structural elements of power cables are conductive wires, core insulation, sheath to protect the insulation from moisture and other environmental influences, armor made of steel tapes or wire to protect the sheath with insulation from mechanical damage and anti-corrosion coating or special protective cover (PUE).
In case an object that needs to be regularly supplied with electricity has an extensive cable network, an example of which is a structured cable system,
There are overhead cable lines and disadvantages. These include the still unsolved problem of storm protection, when falling supports, flying foreign objects tear power lines and thus damage the feeders. Exposure to lightning discharges and electrostatic accumulation are also from the discharge of the negative sides of overhead cable lines. If the installation area is at risk, it is necessary to ensure grounding, or use power cables for underground installation. A line break can provoke not only a collapsed branch: in winter, overhead lines are at risk of sagging and a cliff due to the accumulation of snow and ice on them. Nevertheless, all these disadvantages are related to a rather low degree of probability, and repeatedly overlap with pluses. The main of which is cost.
Methods of installation and installation of overhead cable lines
Lay the overhead cable line must necessarily be specialists who have not only certification for electrical safety, but also admission to climbing works. It is necessary to strictly observe the rules of labor protection, to use means of protection. This is due to the fact that unlicensed installation companies, as a rule, try to reduce the cost of the work performed. And save, first of all, on the purchase of safety equipment for installers. In this regard, industrial accidents are not uncommon, when instead of a cat, hooks and belts household appliances such as “hooking a foot”, working without a safety belt, tying a simple armpit rope and
An overhead cable line is fairly easy to install if a plan is approved before it and the attachment points are examined. One of the indispensable conditions for proper laying of overhead cable lines is the absence of cable friction on objects, which over time will lead to deterioration and abrasion of insulation, and if the weather in the region is unfavorable, and the external environment is aggressive, then insulation deterioration will be accelerated several times.
To avoid undesirable effects, FlexTender technology is often used when laying overhead cable lines. Aluminized (aluminized) or galvanized steel wire is coiled into a spring, like a spiral. It is pulled between two objects, a cable and an auxiliary cable are placed inside the helix. Under tension, the spiral unfolds, providing optimal flexibility, resilience and protection against external damage. The ends of the FlexTender are fixed at two points between two objects of the overhead cable line, there is also an intermediate mounting of the power element and the cable.
Such a helix can be made in an artisanal way from ordinary galvanized wire, and it will even have some advantage: you can first install the power element and cable, and then wind the wire on it. But this has economic feasibility only in the case of a small length of overhead cable line.
Fastening of the power element
When laying overhead cable lines, it is necessary to determine, as mentioned above, the attachment points of the cable and the power element. The latter includes a cable, rope, wires, which provide additional structural strength and are a kind of “skeleton” of SCS. The determination of the points will make it possible to calculate the minimum margin of safety for a known span length and calculate the required one, which should significantly exceed the minimum one. The calculation is made on the basis of extreme situations: storm, wet snow, thunderstorms. Since the responsibility for damage caused by the collapse of the incorrectly calculated structure is the installation organization. Therefore, when installing overhead cable lines, the calculation is made and a multiple safety margin of the power elements is always laid.
The list of permissible fastening elements of the power element includes:
- fittings mounted in the main wall;
- special wall anchors;
- massive roof beam;
- specialized rack.
Inadmissible fastening elements of the power section of an overhead cable line include:
- window frames;
- doorway boxes;
- decorative designs.
All unreliable elements of an overhead cable line, as a rule, give, apart from the danger of being torn up by the root with increasing cable weight, some backlash. Backlash when fastening leads to the mobility of the node of the power element of an overhead cable line, which, in turn, is the cause of the destruction of the node. The installation of power elements at the fracture, that is, with twists, on two or more faces, with sharp turns, can lead to the same. Kinks and breaks can also be caused by the appearance of “lambs” when unwinding a cable. “Lamb” is a half-knot resulting from the partial torsion of an element; it leads very quickly to the breaking of metal fibers.
Hanging the power element when laying overhead cable lines is also very important to carry out correctly, depending on what type of cable is used – self-supporting or normal. In the self-supporting power line cable, an additional power element is used, the usual cable should be suspended with a cable, wire or rope. As a rule, the most commonly used wire or steel wire coated with zinc or brass, with a diameter of 3-5 mm. Cables of larger diameter are protected by polymer insulation. They are fixed, as the self-supporting cable, at two points between the spans. In this case, the rule of exclusion of potential difference occurrence must be observed: if the power element is fixed on the reinforcement of the bearing walls of two buildings, then due to the potential difference, a weak electric current may flow through it, which will lead to undesirable consequences, such as interference in the cable. Therefore, in order to avoid such problems, when laying an overhead cable line, the power elements are grounded, usually from both sides.
In an overhead cable line, the power cell must have a light slack, since a strongly stretched wire gives an additional load. According to SNiP
Hanging the cable on the power element
If the cable is not self-supporting, and there is a need for a power element, you should choose one of two ways to join: either on the ground, prior to installation, or in parallel with the installation of an overhead cable line. According to SNiP
The technology in which the power element is mounted on the ground, and then rises, is rather doubtful: yes, it is much easier to fasten the ties themselves, but when lifting the cable, it is much easier to damage it. Suppose it is only when laying the span of overhead cable lines of small length.
Long spans are pulled first with a power element, then a cable is fed through it at the sliding clamps. The cable is fixed at the starting and ending point and should hang freely. After that, it can already begin to fix point by point. If laying an overhead cable line implies the use of some kind of structures, then there is no need to use cables or wires: the role of the power element is performed by beams, reinforcement, and so on.
Overhead power lines and low-voltage networks are also satisfied on the supports. Supports are classified by type of production and type.
Supports, poles and masts of overhead cable lines on the material are divided into:
It should be noted that according to regulatory enactments, metal supports may be used only in overhead cable lines with voltage above 1 kV.
Supports, poles and masts of overhead cable lines by type are divided into:
- Intermediate. Intermediate support is a single pole, which is placed in very long spans, where cable slack under its own weight can pose a threat of breakage.
- Anchor Installed on the transitions, providing additional structural strength.
- Corner. They are installed at the corners of the overhead cable line, which prevents the formation of bends and kinks in the cable.
- A-shaped. Such supports are installed in places of soldering of wires for installation of dischargers. Discharger is a device designed to limit overvoltages in electrical networks.
When laying overhead cable lines with supports, some temporary structures are allowed. As an example, we can add a sample of non-galvanized single-core wires. Such wires are fixed on supports on pin insulators with wire knits or special clips. Connection of wires can be any – from thermite welding Connect wires with special connecting clips, electrocontact or thermite welding, depending on their type. High-voltage power lines are usually aluminum, steel / aluminum or pure steel. Attach them to the pin or suspension insulators (garlands) overhead cable lines supporting and tension locks.
Fiber Optic Cable Laying
In recent years, it has been necessary to lay fiber optic cable as an overhead cable line, with the advantage given to laying along power lines. This approach has several advantages:
- the coincidence of the lines of transmission lines with the directions of transmission of dispatch-technological information, including the use of free channels for commercial communication;
- no need to allocate land for the highway;
- reducing the cost of construction and installation works;
- a significant reduction in construction time, since the construction of fiber optic lines on power lines is simpler and more technological than the underground installation;
- reducing the number of mechanical damage compared to OK, laid in the ground or sewage;
- significant reduction in operating costs.
However, there are some limitations when laying overhead fiber-optic cable lines. Thus, power lines are constantly under voltage, often subject to accumulation of a statistical discharge, which gives a tip-off in all cables. Installation of the fiber should be done when the power line is disconnected, to which not all owners give their consent. “It is necessary to obtain permission from the owners of the overhead line to perform work, including a power outage, which is governed by the rules of work. In addition, staff must be trained and have access to work on power lines and steeplejack work, ”experts say. In such a situation, an additional gasket along its line, or a contract on a parity basis, will be optimal.
When installing a fiber optic line, the latest technology in the field of design research using precision distance tools is applied. Our company, if necessary, uses, in particular, integrated aerophotography, high-resolution photography, laser-location method of shooting. All this allows us to develop such a concept of laying a fiber optic cable overhead line, which implies the lowest consumption of materials at high efficiency; speed of installation and ease of maintenance; durability; intuitive cable routing, optimal suspension method.
How to determine the reliability of the cable? With tractive effort in the process of laying overhead cable lines, the cable sheath does not give gaps, the sheath does not break at the fixed edges. In order to avoid problems with poor quality products in the future, only certified and tested cable and power elements are purchased. The resistance of self-supporting optical cables to tensile strength is checked by our experts according to the existing method E1 for assessing the tensile strength of optical cables (GOST R IEC794-1-93 "Optical cables. General technical requirements") However, taking into account the fact that GOST is outdated, the requirements for laying overhead cable lines have been revised by us in the direction of significant tightening.
Our work is our responsibility
Over the years of work on the market of laying overhead cable lines, we came to the conclusion that our experience and strict adherence to safety and operating instructions for various types of facilities allowed us to guarantee the highest quality of work. Certified specialists, who are all our employees – from installers to engineers – is another guarantee that the laying of the line, whether power or communication, will be excellent. This process can be observed by the client from the moment of inspecting the place of work, then at the design stage e, and finally – during the installation, testing and launch.