The type of supports used has a significant impact on the condition of power lines. For 100 years, the wooden pole remained one of the main structures of overhead lines (OL).
Only in the 60s of the last century it began to be made with protective impregnation. Then instructions were given on the use of antiseptics, but they were poorly implemented, which led to decay of the supports. The ubiquitous transition to reinforced concrete poles did not solve all the problems, since they revealed disadvantages that are not inherent in wood products:
- impact brittleness;
- low bending strength;
- significant weight;
- presence of leakage currents.
Benefits
The wooden pole will never be written off due to the following benefits:
- Small cost.
- Light weight.
- When a wooden pole falls, the weight of which is 3 times less than reinforced concrete, it hangs on the wires without the "domino" effect characteristic of heavy poles.
- Irreplaceable in areas with high seismicactivity.
- Better withstand wind loads.
- High dielectric performance.
- Long service life if properly manufactured (up to 40 years).
- No special maintenance needed.
Flaws
Along with the advantages, the wooden support has disadvantages.
- Impregnation compositions may contain harmful substances that are in the air of the working area (fuel oil, kerosene, creosote, etc.). Oil-based antiseptics are especially harmful. In addition, they have an increased fire hazard.
- Logs must be made with the required diameters and tapers.
- Quality products are obtained by winter logging and drying under a canopy for 6 months. Here it is necessary to treat the logs with an antiseptic so that they do not rot.
Materials
Wooden power transmission pole is made from coniferous trees, where the resin is a natural preservative and antiseptic. Northern pine, which has high strength and elasticity, is in the greatest demand. The problems that reinforced concrete poles have due to their fragility are never created by wooden supports (photo below - loading of finished products).
Shale or creosote oil is used for impregnation, as well as mixtures containing copper, chromium, arsenic. Additionally, with antiseptic treatment, the supports are treated with fire retardants (flame retardants). This allows you to bury the posts directly into the ground, without concretestepchildren, which increases their service life.
Pine products have the highest absorbency. If spruce and larch are used for supports, it is much more difficult to impregnate them.
Impregnation allows you to bury the posts directly into the ground. Only here it is necessary to additionally protect the ends with protective paste or covers. It is important to dry the wooden support before impregnation for up to 3 months. Fastening to stepsons made of reinforced concrete leads to splitting of wood under wire rod bandages.
Important! For the manufacture of poles, the lower part of the tree (butt) is used, where there are fewer branches and a 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:
- light: d=140 mm; D=160-220mm;
- medium: d=160 mm; D=180-235mm;
- 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 it is 95 kNm.
Criteria for selecting a wooden support
- Northern winter-cut pine is used as material.
- At the top of the column, the thickness is at least 16 cm.
- An aqueous solution of CCA is used as an impregnation.
- The entire support or the lower part is impregnated at the factory under a pressure of 12-14 atm.
- Technological holes are made before impregnation.
- The impregnation depth is 85% of the outer layer of wood - sapwood (up to 40mm).
- The impregnation process is completed if the color of the support is gray-green. If it is brown or brown, this means that the reaction has not yet ended. The border should be visible on the cut of the log.
- Props are sold in grades C1 and C3 with a complete set of sizes.
Features of impregnation of supports
Poles are installed in the ground without stepchildren. The ends are impregnated more than the side surface. During operation, up to 90% of the protective composition is washed out of them. To prevent this, the top end is covered with a galvanized roof measuring 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, the wood under the supports is impregnated with XM-11 protective agent in terms of dry s alt in the amount of 13-15 kg/m3. When purchasing logs for poles, you should find out under what conditions they were made, since in some specifications this amount is underestimated by 2 times. Not all manufacturers correctly maintain the manufacturing technology of products. A quality control organization is required here, although a specialist can determine it visually.
Technology for the production of poles
The process includes 4 important steps.
1. Debarking
The bark with the bast is removed on a specialized machine. Only after that the trunk begins to dry. Sapwood should be touched to a minimum, since it is it that is well impregnated with an antiseptic. If the entire top layer is chipped, the durability of the support will be greatly reduced due to the fact that it will be more susceptible to decay. Then a wooden support,the dimensions of which meet the requirements are sorted by purpose. Some manufacturers dry without removing the bast, which makes it possible to prevent cracking of the wood. Then the bast is removed, as it will interfere with the impregnation process.
2. Drying
Moisture removal is a long and energy-intensive process, on which the quality of impregnation depends. Under-dried wood cannot be impregnated. Its humidity should be reached up to the level of 28%. Drying is done naturally in stacks (2-5 months) or with warm air in drying chambers circulated by fans (7-10 days).
3. Impregnation in autoclave
A vacuum is created in the chamber, pulling out excess moisture. Then the logs are closed with an aqueous solution of an antiseptic, after which the pressure in the chamber rises to 14 atm. After the solution is drained, and a vacuum is created there again. The best impregnation composition is Finnish-made CSA antiseptic. Domestic analogues are made from production waste and contain impurities that reduce the depth of processing and contribute to the leaching of the composition from the wood.
4. Fixation
Impregnation composition contains harmful substances. Logs are aged for some time. In this case, the formation of insoluble antiseptic compounds in the wood structure occurs. The medium temperature must be positive. To speed up the process, the supports are autoclaved with superheated steam. Canadian manufacturers treat logs with special compounds, thereby increasingproduct durability.
VL supports
Installation of wooden poles is carried out on the 3rd class overhead lines, where the rated operating voltage is 1 kV or less. The most common intermediate supports that serve to support the wires. In addition, they perceive wind loads, as well as the weight of the reinforcement and their own. On their own, they may not withstand the forces that arise along the line if a break occurs. This load is perceived by anchor supports with the location of additional struts along the axis of the overhead line. Basically, they serve to create tension in a section of wires. To perceive transverse loads, anchor supports are used with the location of struts or "legs" in the perpendicular direction.
There are also corner supports that take longitudinal and transverse loads. They are installed to rotate the lines.
Installation of wooden poles is carried out with precise marking of places, and assembly - with a tight fit of parts.
The gap where the cuts are made should not be more than 4 mm. The mating points are tightly fitted. Holes are being drilled.
Maintenance and repair of wooden poles
Wooden power transmission line support is subject to periodic inspections and repairs. In the summer, at a depth of 30-50 cm, the depth of wood decay is checked. If a log is 25 cm in diameter and the rot is more than 3 cm, it is considered unusable and must be replaced.
Major overhaul of lines, where mostly woodensupports, is done at least every 6 years. The rest of the repair work is being carried out in a time frame that depends on available resources.
The fire hazard of wooden poles requires labor-intensive operations to reduce it. In the presence of wooden attachments, a ditch 0.4 m deep breaks out around and grass with shrubs is removed.
Parts from supports are changed to new ones when the line is running. Here it is necessary to take into account that the loads on the parts of the structure may exceed the calculated ones.
If the poles deviate from the vertical by an unacceptable amount, additional loads can cause the position to change and the wires to lash or touch the parts. Displacements occur due to weakening of the foundation or embedment of the base of the support, ground displacement, loosening of connections.
Surveying is carried out with steel cables mounted on a stand. The base is dug to a depth of up to 1.5 m and the support is straightened with a traction mechanism. Then the pit is filled and rammed.
When the rack warps due to a loose connection with the bandage, it is straightened without shifting the stepchildren.
A bandage is installed on a rotten rack. Before that, the rot is removed and the post is covered with antiseptic paste.
Damaged parts are reinforced with temporary overlays made of wood or metal, using half-clamps, bolts and bandage wire.
Parts are checked for compliance with design parameters before being taken to the track.
To increase the life of the racks, they should be additionally impregnated during operation with diffusionway. Antiseptic bandages are installed on the underground and aboveground parts of the support and on the joints. An antiseptic paste is applied to the cracks and on the tops of the racks with attachments.
Due to the fact that the weight of the wooden support is small, heavy equipment is rarely required for repairs.
A support that cannot be repaired is relieved of all loads and replaced with a new one using special equipment.
Conclusion
Impregnated wooden support is not worse than reinforced concrete, and in some cases even better, thanks to a lot of advantages. For them to be more actively applied in practice, an industry standard is needed. This will establish uniform requirements for all manufacturers so that the quality is guaranteed.
