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Mechanical calculation of wires, cords, self-supporting cables of communication and power lines



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LineS - program package for designing overhead power and communication lines (OHL, FOCL OHL, FOCL). The calculating part of the program has been used since 1985 beginning with SM-4 EVM (System of mini-computers developed in USSR in 1970-80s).

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Classical mechanical calculation. Tales into account all the co-relations of critical spans.

LineMech program calculates the loads, critical spans, stresses, tension and sag of the wires, cords, self-supporting cables (including those of fiber optic communication lines, FOCL), power lines of any voltage for reference (EIR) and mounting modes. The calculation results are given in the order, corresponding to “manual” calculations, as it is done in reference books.

The mechanical calculation theory and an example of “manual” calculation is given on “Theory and Practice” page.
The calculation is performed based on permissible tension method.

According to 2.5.185 of EIR, the mechanical calculation of optical ground-wire cables, optical phase-wire cables, self-supporting optical cables should be done considering the reference loads based on permissible tension method, following all other requirements both for wires and cords of overhead lines, see the section of EIR “Fiber optic communication lines on overhead lines”.

LineMech program helps to:

1. Sort out the tension (stress) in a wire, cord, self-supporting cable considering:
-    Permissible tension (stresses) affecting wires, cords, self-supporting cables, according to EIR, National Standard, Technical Conditions;
-    Permissible tension affecting load-bearing constructions (supports, portals, etc.);
-    Possible additional decrease of the loads on load-bearing constructions with the reserve in clearance.
2. Define the overall span for a typical project of supports, portals.
3. Select a typical project for mass supports of the line based on the clearance;
4. Compare the sag of wire, cord and self-supporting cable for different modes;
Sort out the stress in the cord, optical ground-wire cable, considering the required distance between the wire and the cord, to decrease the load on supports.
5. Carry out expertize and verify the measured sag and stressed.
6. Define the reference tension (stresses) based on sag and stress at different temperatures for wires of existing power lines.
7. LineMechCad version of the program – prepare the patterns of supports-spotting and sag of wires, cords, cables at different temperatures.

The calculation results show load-per unit length and equivalent loads for further consideration of the loads to load-bearing constructions (supports, portals, etc.), resulting from the stress of the wires, cords, self-supporting cables and different effects of climatic conditions, by the line designer.

The user is given a warning in case the reliability coefficients to standard loads are used not according to 2.5.11 of EIR-7; in the source data they equal 1 by default.

The program allows calculating for new lines as well as for the reconstructing using the requirements of both EIR-7 and earlier versions.

This is one of the most effective programs from the point of view of optimizations: an average specialist spends about 5 days on “manual” calculation, an experienced one – three days, while the program performs the calculation for all the modes within seconds.
The data on wires, cords, and self-supporting cables are saved in the reference file accessible for editing and updating.
When using self-supporting cables of fiber optic communication lines (FOCL) it is necessary to ask their characteristics from the manufacturer for each particular project.

Figure 1. Inputting source data for calculation

The program has an excessive number of modes for calculation, up to +70C (the requirements for overcrossing the railways); the first modes are loading modes (maximum loads, lowest temperatures), then the modes necessary for other calculations, including those for defining the equivalent span, and finally – mounting modes (for strain attachment fittings only).
If it is necessary to consider the additional warming up of the wires due to the electrical current or sun radiation, correct the maximum temperature.
Besides the description of the input source data, “Help” file of the program includes the recommendations on using the calculation and defines its place in the project.

The calculation results are ported to Excel from where they could be ported to project documentation of any format.

Figure 2. Calculation results

The from with calculation results contains all the source data, including reference data (for the sake of control), reference values for critical spans, load per unit length and equivalent loads, stresses, tension and sag for given span lengths and modes.

In LineMechCad version of the program installed AutoCad of any other graphical package supporting dxf format is started to prepare the supports-spotting patterns on the line route profile and sagging curves of the wires, cords, and cable at different temperatures.

Figure 3. Source data input for supports-spotting patterns and sagging curves.

The result of using AutoCad is the required pattern for supports-spotting on the line route profile (see Figure 4) used to be printed on the film for the paper version of the profile or as a block of AutoCad or any other graphical package.
The sagging curves are used to evaluate the crossings clearances at different temperatures and endurance of insulator strings at the lowest temperatures.

Figure 4. Supports-spotting pattern for the line route profile

For more details see the User Guide for the program (Program description. Application.) which could be downloaded along with the demo version.