Wooden support of power lines: photo, dimensions, weight. Installation and repair of wooden supports
The state of the transmission line is significantly influenced by the type of supports used. For 100 years the wooden support remained one of the main structures of overhead lines (overhead lines).
Only in the 60s of the last century it begando with protective impregnation. Then instructions were given on the use of antiseptics, but they were poorly executed, which led to decay of the supports. The ubiquitous transition to reinforced concrete poles did not solve all the problems, because they had flaws that were not inherent in wood products:
- brittle impact;
- small bending strength;
- significant weight;
- presence of leakage currents.
Wooden support will never be written off due to the following advantages:
- Low cost.
- Light weight.
- When the wooden support falls, the weight of which is 3 times less than the reinforced concrete, it hangs on the wires without the "domino" effect, which is characteristic of heavy poles.
- Indispensable in areas with increased seismic activity.
- Better withstand wind loads.
- High dielectric characteristics.
- Long service life with proper manufacturing (up to 40 years).
- Do not require special maintenance.
Along with the advantages of wooden support has disadvantages.
- Impregnating formulations may contain harmfulsubstances that are in the air of the working zone (mazut, kerosene, creosote, etc.). Especially harmful are oil based antiseptics. In addition, they have increased fire hazard.
- Logs must be made with the necessary diameters and taper.
- Quality products are obtained during winter felling and drying under a canopy for 6 months. Here it is necessary to treat logs with an antiseptic so that they do not rot.
Power line support wooden is made from coniferous tree species, whereresin is a natural preservative and antiseptic. The greatest demand is for the northern pine, which has high strength and elasticity. The problems that ferro-concrete pillars have due to their fragility never create wooden supports (the photo below is the loading of the finished product).
For impregnation, slate or creosoteoil, as well as mixtures containing copper, chromium, arsenic. Additionally, with antiseptic support, the supports are treated with fire-fighting agents (flame retardants). This allows you to dig in the pillars directly into the ground, without concrete stepsons, which increases the service life.
The highest absorbency is available in pine products. If fir and larch are used for supports, it is much harder to impregnate them.
Impregnation allows burrowing polesdirectly 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 impregnating it for up to 3 months. The attachment to the stepsons of reinforced concrete leads to the splitting of the wood under the bandages from the wire rod.
Important! For the production of poles, use the lower part of the tree (pile), where there are fewer branches and a more uniform 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:
- light: 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 a log diameter of 190 mm, the maximum bending moment is 55 kNm, and for 240 mm, 95 kNm.
Criteria for choosing a wooden support
- The material used is the northern pine of winter cutting.
- At the top of the column, the thickness is not less than 16 cm.
- As impregnation, an aqueous solution of CCA is used.
- The whole support or the lower part is impregnated in the factory at a pressure of 12-14 atm.
- Technological holes are made before impregnation.
- Depth of impregnation is 85% of the outer layer of wood - sapwood (up to 40 mm).
- The impregnation process is finished, if the color of the support is gray-green. If it is brown or brown, it means that the reaction to the end has not ended. The boundary should be visible on the log cut.
- Supports are sold in classes C1and C3with the complete set on the sizes.
Features of impregnation of supports
In the ground, the pillars are installed without stepchildren. The ends are impregnated more than the side surface. In operation, up to 90% of the protective composition is washed out of them. To prevent this, the top is covered with a galvanized roof with a size of 250x250 mm, and the bottom is covered with a flat material that does not allow moisture.
In accordance with GOST 20022.0-93, the wood under the supports is impregnated with the protective agent XM-11 in terms of dry salt in an amount of 13-15 kg / m3. Acquiring logs for poles, it followsto find out, under what conditions they were made, since in some specifications this quantity is understated by 2 times. Not all manufacturers correctly withstand the technology of manufacturing products. It requires the organization of quality control, although a specialist can determine it visually.
Technology of production of supports
The process involves 4 important steps.
On a specialized machine, the bark is removedbast. Only after this the trunk begins to dry. Zabolonovaya wood should be affected at a minimum, because it is well impregnated with antiseptic. If the entire top layer is stuck, the longevity of the support will be much reduced due to the fact that it will be more susceptible to decay. Then the wooden support, the dimensions of which meet the requirements, is sorted according to the purpose. Some manufacturers produce drying without removing the bast, which makes it possible to prevent the cracking of wood. Then the bast is removed, as it will interfere with the impregnation process.
Removal of moisture - a long and energy-consumingThe process on which the quality of impregnation depends. Dried wood can not be impregnated. Its moisture content should be reached to a level of 28%. Drying is done naturally in piles (2-5 months) or warm air in drying chambers, which is circulated by fans (7-10 days).
3. Impregnation in an autoclave
In the chamber, a vacuum is created, pullingexcess moisture. Then the logs are closed with an aqueous solution of antiseptic, 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 composition is the antiseptic of the SSA of Finnish production. Domestic analogues are made from industrial waste and contain impurities that reduce the depth of processing and contribute to the elution of the composition of wood.
The impregnating composition contains harmful substances.Logs lie awhile. This leads to the formation of insoluble antiseptic compounds in the structure of the wood. The temperature of the medium must be positive. To accelerate the process, the supports are treated in an autoclave with superheated steam. Canadian manufacturers treat logs with special compounds, thereby increasing the durability of products.
Supports of overhead lines
Installation of wooden poles is carried out on VL-3class, where the rated operating voltage is 1 kV or less. The most common intermediate supports, which serve to support the wires. In addition, they perceive wind loads, as well as the weight of the armature and its own. Independently, they can not withstand the forces arising along the line, if there is a breakage. This load is perceived by anchor supports with the arrangement of additional struts along the axis of the overhead line. Basically, they serve to create a stretch of the wire section. To perceive lateral loads, anchor supports are used with the arrangement of struts or "legs" in a perpendicular direction.
There are also angular supports that perceive longitudinal and transverse loads. They are installed to rotate the lines.
Installation of wooden supports is done with precise marking of places, and assembly - with a tight fit of parts.
The clearance, where the cutting is done, should not be more than 4 mm. The mating points are tightly fitted. The holes are drilled.
Maintenance and repair of wooden supports
The support of the power transmission line is subject to periodicinspections and repairs. In the summer, at a depth of 30-50 cm, the depth of decay of the wood is checked. If the diameter of the log is 25 cm and the decay is more than 3 cm, it is considered unusable and should be replaced.
Major overhaul of the lines, where most of the wooden supports are installed, is done no less than 6 years from now. The rest of the repair work is performed within the timeframe, depending on the available resources.
The fire hazard of wooden supports requires labor-intensive operations to reduce it. In the presence of wooden prefixes a ditch with a depth of 0.4 m is pulled out and a grass is removed with a bush.
Details from the supports are changed to new ones with the line running. Here it is necessary to take into account that on the parts of the structure the loads can exceed the calculated ones.
If the columns deviate from the vertical byan unacceptable value, additional loads can cause a change in position and clashing wires or touching the parts. Displacements occur because of the weakening of the foundation or the fixing of the foundation of the support, the displacement of the ground, the weakening of the joints.
The bearing is made with steel cables reinforced on the rack. The base is dug to a depth of 1.5 m and the traction mechanism straightens the support. Then the pit is buried and rammed.
When the stand is skewed due to the weakening of the connection with the bandage, it is straightened, not displacing the stepchildren.
On the decayed rack establish a bandage. Before this rot is removed and the pillar is covered with antiseptic paste.
Damaged parts reinforce the temporary lining of wood or metal, using half-hammers, bolts and a shroud wire.
The parts before going to the road are checked for compliance with the design parameters.
To extend the life of racks, theirshould be additionally impregnated during operation by diffusion. Antiseptic bandages are installed on the underground and aboveground parts of the support and at the junction points. In the cracks and on the tops of racks with attachments, antiseptic paste is applied.
Due to the fact that the mass of the wooden support is small, during repair rarely requires heavy equipment.
The support that can not be repaired is released from all loads and replaced with a new one using special equipment.
Wooden support with impregnation is not worsereinforced concrete, and in some cases even better, due to the mass of merits. In order for them to be used more actively in practice, an industry standard is needed. This will allow to establish uniform requirements for all manufacturers, so that quality is guaranteed.