Overhead transmission line (OTL) design is labour-consuming task, which often solve multiple sub-unit of project organization. That's OTL design automation should comprehend the entire technological chain [2].
Automation provides a rational function distribution between man and computer. CAD system of overhead TL and EHV (SAD) consists of technical and documentary systems. More detailed CAD OTL block diagram shown in fig. 1. The technical system includes linear, construction and mounting-building sub-systems [5].
Figure 1 - Block diagram of CAD OTL and EHV (Animation: volume - 29,8 KB, size - 530x489; number of frames - 4, the delay between frames - 250 ms delay between the last and first frames - 600 ms, the number of repetition cycles -5)
Documentary system consists of ten units.
The work practical value is to use the results of working in the learning process on "Electrical Systems" department of DonNTU.
The work actuality is in updating the existing working of students and teachers on OTL CAD subject. These types of software are technically obsolete and require modernization at the level of modern operating systems, programming languages, computer capabilities and applications software packages. A very important aspect is the consistency of new programs engineering instruction-2006. Thus, the new OTL CAD and EHV should be made on the basis of new recommendations and calculations [7].
The master project aim is development of present-day algorithms for making the OTL and EHV CAD programs.
Main idea of master project is the making of new mathematical methods of calculation and algorithms for software modules of CAD.
Subject of research work is a present-day OTL and EHV CAD software Object is a system of automatic OTL and EHV design, improvement it.
An essential part of the master's work is to develop methods of calculating the electric field intensity under the OTL wires.
The method is based on the well-known theoretical approach, according to which OTL wires locate near the flat surface of a conducting medium (earth).
In this method the multiconductor line is considered consist of 3 very long wires with charges ? per unit length (an index of the charge corresponds to the number of wire), laid parallel to the earth surface. Suspension height and radius of each wire are known. Air permittivity is known also [1].
Consider some arbitrary point M in dielectric and find its potential. The potential of point M will be equal to potentials sum, produced by each wire and its looking-glass reflection:
where
- is the distance from point M to the looking-glass reflection of the first wires;
- is the distance from point M to the first wire.
Potential component of point M from the second wire and its looking-glass reflection:
.
Thus
.
Algorithm of potential calculating in arbitrary point M:
1. Calculate the potential coefficients ? [m/F]:
where
is the distance from the first wire, which placed the point M, to its looking-glass reflection, 
is the distance from the first wire to the second.
Matrix is formed
.
2. Calculate the capacitance ratios [F/m]
3. We believe that the potentials are known and are equal to the rated network voltage:
Solve the system of equations, called the second group of Maxwell's formulas
4. Determining potential at a given point M
An important part of the master's work is to develop methods of "Great passage" wire calculating of the linear subsystem OTL CAD.
Under the title "Great passage" is meant the passage of overhead TL in condition of flat terrain across the wide water space and in mountain terrain through the various ravines.
To calculate the TL "Great passage" means to calculate the overhead TL wires, which is required to determine the line dimensions over the water surface or mountain terrain mark [9].
As is known, the so-called mechanical calculation overhead TL wires, in principle, can be made by approximate or exact methods.
The question of the permissible degree of error is solved with a particular design depending on the nature of the route line.
The main purpose of the proposed method is development for practical applications of the suitable string theory - the so-called theory of chains of equal resistance and the working on its basis the decision of many problems that arise in the calculation of great passage.
In the present in parallel with the development and improvement of rigorous string theories is very important the development of simple and practically acceptable approximate methods of calculation and further experimental studies.
An existed method of mechanical calculation of overhead TL has several disadvantages:
1) don’t take into account the weight;
2) sag is determined by normative combination of climatic conditions on the normative temporary and constant load, which in general case can be exceeded;
3) don’t take into account the heating wires of electric current;
4) the actual span length may differ from the project;
5) it should be borne in mind that the sag adjustment at mounting is executed in a transitional passage;
6) there are some difficulties in accounting for residual deformations of wires;
7) own weight load is accepted uniformly distributed;
8) the depth of the foundation is assumed constant;
All these circumstances give reason to believe that the wire calculations at great passage TL, using the catenary line theory may under certain circumstances lead to sufficiently reliable results [4].
CAD software overview
There are many OTL CAD software today. Consider the most popular in our region.
A successful implementation of the OTL and EHV CAD is Russian software of system Energy CS Line, meant for automate of design of the OTL mechanical par, fiber-optical cables, fiber-optical link lines, flexible bus-bar open switching devices, flexible current wire. This complex provides database maintenance of executed earlier calculations, a database of reference information on wires, cables, overhead line support, insulators, climatic region [8].
The most powerful software system for today is TL CAD - 2008. It is intended to automate the design of overhead power lines with voltage 35 kV and above. The main advantage is the constant improvement of CAD in the form of new modules that have appeared already in 2009.
A list of the main results and prospects
Mechanical calculation is a basic method of overhead transmission line designing. At the moment of author's abstract writing there was a program developed with the use of the Delphi programming language. Today one of the most essential disadvantages of this program is use of DOS – interface. That’s why the main task today is development a program with Windows – interface, as it allows to make a visualization and database modernization.
References
1. Правила улаштування електроустановок. Глава 2.4, глава 2.5 із зміною №1. – К.: ГРІФРЕ, 2006. – 126с
2. Журнал CADmaster [Электронный ресурс].-Режим доступа: ссылка, http://www.cadmaster.ru.
3. Офіційний сайт групи компаній CSoft [Электронный ресурс].-Режим доступа: ссылка, http://www.csoft.ru.
4. Ильичев Н.Б. Расчет и проектирование ВЛ, ОРУ и ВОЛС в среде EnergyCS Line/ Н.Б. Ильичев//М.,2007 – С. 12–16.
5. Шпак Ю.О. Delphi 7 на прикладах/ Ю.О. Шпак, Ю.С. Ковтанюк//К.: Юніор,2003 – 384с.
6. Ильичев Н.Б. Программный комплекс «EnergyCS Line» V 3.5 . Руководство пользователя./ Н.Б. Ильичев//Иваново, 2007 – 79 с.
7. ЛЭП 2009 - «Розрахунок навантажень на опори та фундаментів» [Электронный ресурс].-Режим доступа: ссылка, http://www.bsapr.ru.
8. Матеріали Другої всеросійської науково- практичної конференції 2006г [Электронный ресурс].-Режим доступа: ссылка, www.ohl.elsi.ru/2006.
9. Доклад Молчанова О.В., Титенсккого К.С. [Электронный ресурс].-Режим доступа: ссылка, http://www.ohl.elsi.ru/sbornik_trudov/6.pdf.
10. Електроний журнал [Электронный ресурс].-Режим доступа: ссылка, http://www.sapr.ru.
11. ГОСТ. 13109-97 «Нормы качества электрической энергии в системах электроснабжения общего назначения».
12. Методические указания по контролю и анализу качества электроэнергии в системах электроснабжения общего назначения. Часть 1. Контроль качества электрической энергии (РД 153-34.0-15.501-00).
13. Методические указания по контролю и анализу качества электрической энергии в системах электроснабжения общего назначения. Часть 2. Анализ качества электрической энергии (РД 153-34.0-15.502-2002).
An important remark!
While writing the current author's abstract the master’s work is not finished yet. The final completion will be by the 1st December 2010. You may obtain the full work’s text and all the materials from the author or his supervisor after the stated date.
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