The condition of power transmission lines is significantly influenced by the type of supports used. For 100 years, wooden support remained one of the main structures of overhead lines (OHL).
Only in the 60-ies of the last century it began to do with protective impregnation. Then instructions were given on the use of antiseptics, but they were poorly implemented, which led to the decay of supports. The ubiquitous transition to reinforced concrete pillars did not solve all the problems, because they showed flaws that are not inherent in wood products:
- brittleness upon impact;
- small bending strength;
- considerable weight;
- presence of leakage currents.
The wooden support will never be written off due to the following advantages:
- Small cost.
- Low weight
- When a wooden support falls, the weight of which is 3 times smaller than reinforced concrete, it hangs on wires without the domino effect typical of heavy pillars.
- Indispensable in areas with high seismic activity.
- Better withstand wind loads.
- High dielectric characteristics.
- Long service life with proper production (up to 40 years).
- Do not require special maintenance.
Along with the advantages of wooden support has disadvantages.
- Impregnating compounds may contain harmful substances that are in the air of the working area (fuel oil, kerosene, creosote, etc.). Especially harmful antiseptics on an oil basis. In addition, they have a high fire risk.
- Logs must be made with the required diameters and taper.
- High-quality products are obtained during the winter felling and drying under a canopy for 6 months. Here it is necessary to treat the logs with antiseptic, so that they do not rot.
The wooden pylon is made of coniferous trees, where the resin is a natural preservative and antiseptic. The greatest demand is northern pine, which has high strength and elasticity. The problems that reinforced concrete pillars have because of their fragility never create wooden supports (the photo below shows loading of finished products).
Apply shale or creosote oil to impregnation, as well as mixtures containing copper, chromium, arsenic. Additionally, antiseptic supports are treated with flame retardants (flame retardants). This allows you to bury poles directly into the ground, without concrete stepsons, which increases their service life.
The highest absorbency possess products from pine. If spruce and larch are used for supports, it is much more difficult to saturate them.
Impregnation allows bury pillars directly into the ground. Only here it is necessary to additionally protect the ends with a protective paste or lids. It is important to dry the wooden support before impregnation up to 3 months. Fastening to the stepsons of reinforced concrete leads to the splitting of wood under the bandages of rod.
Important! For the manufacture of pillars using the lower part of the tree (butt), where fewer branches and more homogeneous structure.
Dimensions and strength
The length of the supports is 3,5-13 m. Depending on the diameters in the upper (d) and lower (D) parts, they are as follows:
- lungs: d = 140 mm; D = 160-220 mm;
- medium: d = 160 mm; D = 180-235 mm;
- strong: d = 195-210 mm; D = 210-260 mm.
An important indicator is the strength at the bottom of the rack. For the diameter of the 190 mm log, the maximum bending moment is 55 kNm, and for 240 mm - the 95 kNm.
Criteria for choosing a wooden support
- Northern pine is used as a material.
- At the top of the pillar, the thickness is at least 16 cm.
- An aqueous solution of SSA is used as impregnation.
- The whole support or the lower part is impregnated at the factory under pressure 12-14 atm.
- Technological holes are made prior to impregnation.
- The depth of impregnation is 85% of the outer layer of wood - sapwood (up to 40 mm).
- The impregnation process is completed if the color of the support is gray-green. If it is brown or brown, it means that the reaction has not been fully completed. The border should be visible on the log cut.
- Props sold in grade C1 and C3 with a complete set by the sizes.
Features of impregnation of supports
In the ground poles are installed without stepsons. The ends are soaked more than the side surface. During operation, they are washed out to 90% of the protective composition. To prevent this, the top end is covered with a galvanized roof of size 250x250 mm, and the bottom is covered with a flat material that does not allow moisture to pass through.
According to GOST 20022.0-93, wood under the supports is impregnated with XM-11 protective agent in terms of dry salt in the amount of 13-15 kg / m3. When purchasing logs for pillars, you should find out under what conditions they were made, since in some TU this number is underestimated 2 times. Not all manufacturers correctly maintain the technology of manufacturing products. It requires the organization of quality control, although the specialist can determine it visually.
Production technology supports
The process involves 4 important steps.
On a specialized machine removed bark with bast. Only after that the trunk begins to dry. Sapwood wood should be affected to a minimum, since it is she who is well soaked with antiseptic. If the entire top layer is cut down, the durability of the support will be much reduced due to the fact that it will be more susceptible to rotting. Then the wooden support, the dimensions of which meet the requirements, is sorted by purpose. Some manufacturers produce drying without removing bast, which makes it possible to prevent the cracking of wood. Then bast is removed, as it will interfere with the impregnation process.
Moisture removal is a long and energy-intensive process on which the quality of impregnation depends. Undried wood cannot be impregnated. Its humidity should be reached to the level of 28%. Drying is carried out in a natural way in piles (2-5 months) or by warm air in drying chambers that circulates with the help of fans (7-10 days).
3. Autoclave Impregnation
A vacuum is created in the chamber to draw out excess moisture. Then the logs are closed with an aqueous antiseptic solution, after which the pressure in the chamber rises to 14 atm. After the solution is drained, a vacuum is created there again. The best impregnating compound is antiseptic CCA of Finnish production. Domestic counterparts are made from industrial waste and contain impurities that reduce the depth of processing and contribute to leaching the composition of wood.
Impregnating composition contains harmful substances. Logs are laid out for some time. When this occurs, the formation of insoluble antiseptic compounds in the wood structure. The temperature of the medium must be positive. To speed up the process, the supports are autoclaved with superheated steam. Canadian manufacturers process logs with special compounds, thereby increasing the durability of products.
Installation of wooden poles is made on the class XLUMX OHL, where the rated operating voltage is 3 kV and less. The most common intermediate support for serving wires. In addition, they perceive wind loads as well as the weight of the reinforcement and their own. On their own, they may not be able to withstand the efforts that occur along the line if a break occurs. This load is perceived by anchor supports with the location of additional braces along the axis of the overhead line. They are mainly used to create tension in the wire section. To perceive transverse loads, anchor supports are used with the location of the struts or "legs" in the perpendicular direction.
There are also corner supports, which perceive longitudinal and transverse loads. They are set to rotate the lines.
Installation of wooden poles made with accurate marking places, and the assembly - with a tight fit parts.
The gap where the cuts are made should not be more than 4 mm. Pairing places are tightly fitted. Holes are drilled.
Maintenance and repair of wooden poles
The support of the high voltage line wooden is subject to periodic surveys and repairs. In the summer, at a depth of 30-50, see the depth of decay of wood. If the diameter of the log is 25 cm, and the rotting is more than 3 cm, it is considered unsuitable and must be replaced.
The overhaul of the lines, where wooden supports are mostly installed, is done at least 6 years. The remaining repairs are made in time, depending on available resources.
The fire hazard of wooden poles requires laborious operations to reduce it. In the presence of wooden consoles around a ditch pulled out of the depth of 0,4 m and removed the grass with shrubs.
Details from the supports are changed to new ones when the line is working. Here it is necessary to take into account that the load on the parts of the structure may exceed the calculated.
If the pillars have deviated from the vertical by an unacceptable amount, additional loads may cause a change in position and wire clashes or touching the parts. Displacements occur due to the weakening of the foundation or embedment of the base of the support, the displacement of the soil, the weakening of the joints.
The bearing is produced by steel cables fixed on the rack. The base is excavated to a depth of 1,5 m and the support is straightened by a traction mechanism. Then the pit fall asleep and ram.
When the rack is warped due to the weakening of the connection with the bandage, it is straightened without displacing the stepson.
On the rotted rack set bandage. Before this, the rot is removed and the column is covered with an antiseptic paste.
Damaged parts are reinforced with temporary overlays of wood or metal, using half-sleeves, bolts and retaining wire.
Details before export to the track are checked for compliance with the design parameters.
To increase the life of the racks, they should be additionally impregnated during the operation using the diffusion method. Antiseptic bandages are installed on the underground and above-ground parts of the support and on the joints. Antiseptic paste is applied to cracks and tops of racks with attachments.
Due to the fact that the weight of the wooden support is small, heavy machinery is rarely required for repairs.
The support not subject to repair is freed from all loads and replaced with a new one with the help of special equipment.
Wooden support with impregnation is not worse than reinforced concrete, and in some cases even better, due to the mass of advantages. To make them more actively used in practice, an industry standard is needed. This will establish uniform requirements for all manufacturers to ensure quality.