Special transmission line poles are used for the overhead power lines, vertical structures that hold the wires at height at a given distance from the ground and from each other. Such structures, installed in the open air, shall withstand wind loads for a long time.
Therefore, transmission lines poles are made of different materials, have various shapes and dimensions, differ in their use.
CLASSIFICATION OF POLES
- ultra-long, transmitting high voltage over a long distance – above 500 kV;
- mainline, which are connectors of power stations, individual sections of HVL;
- distribution, supplying energy between settlements;
- consumer, used to provide power to the power consumers.
By the method of wire suspension:
- intermediate, uniformly distributed on the straight sections of the high voltage lines and serving to hold the wires in the retaining clips. If a turn is required, angular transmission line poles are installed that change the direction of the lines at a small angle (15 to 30°);
- anchor transmission line poles are used in places of engineering interruption of straight sections (transitions, obstacles etc.) to create tension of wires or cables. If the turn is made at a large angle (180°), the angle-suspension transmission line poles are installed;
- end poles have a structure similar to the anchor structure and are used at the ends of the high voltage lines to create a one-sided tensioning of cables or wires.
Special types of power transmission line poles, used in special cases, are also available. These include transposition, used to change the location of wires directly on the pole; branching or crossing to connect one or more additional lines to the mainlines; wind-resistant with increased rigidity; transition with the change of the wires height.
By the method of fixing in the ground:
- installed directly into the ground and to be fixed by poured concrete. They are more difficult to install, requiring excavation, placing of formwork and preparation of the appropriate grout. This design is characterized by some bulkiness since hardening of concrete takes time which requires additional efforts to comply with the absolute vertical of the pole. Besides, the location of such structures can not be changed without damaging the integrity of the structure;
- mounted on a specially prepared base or foundation. Such method is most commonly used directly in the settlements where changes to the power supply circuit are not excluded. The foundation itself can be easily moved to another installation point, and in case of its damage the cost of replacing is several times lower than the total cost of the pole. The pole is fastened to the base by bolts, so it is characterized by simple installation, repair and replacement.
- freestanding transmission line poles, which are also divided into single pole in the form of vertical pole or multi-pole consisting of two or more poles;
- poles with anchor stays, in which additional poles are replaced by special extensions with independent fixing in the ground or to the base;
- cable-stayed emergency reserve poles which belong to prefabricated structures for use in emergency situations.
By number of circuits:
- single circuit, for all kinds of voltage;
- double circuit – for 35-330 kV;
- multi-circuit or universal.
- for lines from 0.4 to 1150 kW, which are considered classes – from the lowest to the ultra-high, depending on which they can differ in size and weight, have different structure and height. Also the structures have many differences, depending on the type of voltage – direct or alternating.
STRUCTURE OF POLES
The structure of the poles may include ten or more elements, depending on their purpose and type. However, the main elements are:
- a pole, which is the base of the structures, and the parameters of which define the dimensions of wires (height of placement, number of circuits, direction, etc.);
- struts, taking part of the load on the structure in anchor, angular and branch poles;
- extension or stub for poles, buried in ground;
- brace struts in the form of fasteners, connecting multiple angled poles or one pole with cross-bars;
- cross-bar is used for mounting of wires at established distance between them;
- foundation or base, holding the pole in the ground or on the surface;
- deadbolt required to increase the side surface of the pole base when installed on the surface;
- anchor wires is usually made in the form of cables, increasing the horizontal stability of the structure;
- ground wire peak, which is located at the top of the support for the installation of ground wire;
- extension is used when necessary to increase the height of the pole;
- pole stub is located in the lower part of the pole and is the rest of the pole directly into the ground.