Hava hatları ve yeraltı kablolarının enerji iletim maliyetlerinin karşılaştırılması
Comparison of the transmission costs of overhead lines and underground cables
- Tez No: 14413
- Danışmanlar: PROF.DR. NESRİN TARKAN
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1991
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 135
Özet
ÖZET Bilindiği üzere : elektrik enerjisi, tüketim yerle rinden oldukça uzun mesafelerde üretilip, iletim ve dağı tımı ya hava hatları ya da yeraltı kablo sistemleri ile yapılmaktadır. Bu tez çalışmasının amacı; hava hatları ve yeraltı kabloları ile yapılan enerji iletiminin maliyet yönünden karşılaştırılmasıdır. Bu yüzden, önce enerji iletim sis temlerinin tanıtımı yapılmış, kullanılan kablo ve iletken lerin yapısı, gerilim-değerleri..üzerinde durulmuştur. üçüncü bölümde, hava hatlarına ilişkin elektriksel büyüklükler tanıtılmıştır. Beşinci bölümde hava hatların da kullanılan iletkenler ve yalıtkanlara değinilmiş, hat ların optimum yüklenmesi), böyutlandırılması, oluşan kayıp lar, maliyetler, reaktif kompanzasyon ve akım taşıma kapasitesi anlatılmıştır. Dördüncü ve altıncı bölümlerde önce yeraltı kablo larına ait elektriksel büyüklükler verilmiştir. Daha sonra kullanılan iletkenler, yalıtkanlar, kılıf ve zırh malzemeleri, kabloların tesisi ve soğutma teknikleri anla tılmıştır. Kayıp ve maliyete ilişkin formüller verilmiş tir. Son bölümde tezin amacı olan hava hattı ve yeraltı kablo sistemi ile yapılan enerji iletimi, maliyet yönünden karşılaştırılmıştır. Bulunan sonuçlardan hava hatları ile yapılan enerji iletiminin yeraltı kabloları ile yapılan iletimden özellikle, yüksek gerilimlerde çok daha ekonomik olduğu görülmüştür.
Özet (Çeviri)
SUMMARY COMPARISON OF THE TRANSMISSION COSTS OF OVERHEAD LINES AND UNDERGROUND CABLES An electrical power system can be considered to consist of a generation system, a transmission system, a subtransmission system and a distribution system. In general the generation and transmission systems are referred to as bulk power supply and the subtransmission and distribution systems are considered to tbe the final means to transfer the electric power to the ultimate custo mer. In the past, the transmission system planning and design were based substantially on the planner's past experience. Today the planner has numerous analysis and synthesis tools at his disposal. These tools can be used for design and planning activities, such as - transmission route identification and selection - transmission network expansion planning - network analysis and - reliability analysis. Distribution and transmission systems may be either overhead or underground. For low or medium load densities the distribution system is usually overhead, using poles and open wires mounted on wood cross arms. For greater load densities in the congested areas of cities, the dist ribution system is usually underground, using ducts and manholes under the surface of streets and sidewalks. In the early days of electrical power transmission, when voltages of 11 kV or 3 3 kV were considered high volta ges, copper was mainly used as the material for overhead line conductors. In the meantime, with the expansion of electricity networks, several factors, such as price, weight, availability..and conductivity, have virtually com pelled overhead line engineers to concentrate on aluminium- based conductors, for example AAC = all aluminium conductor ACSR = aluminium conductor steel reinforced (which was also known as SCA, steel^cored aluminium) xlAAAC = all aluminiums-alloy conductor ACAR = aluminium conductor alloy reinforced All conductors suffer from corrosion, which is more pronouieed with bimetallic construction when an electolytic cell can be developed under the right conditions, between the aluminium and the zinc coating of the steel core. The reliability of an actual line is much more difficult to calculate, because it is a function of many influences, such as the size of the loading event (for example one span or several spans) and the degree of utilization of each component, i.e. the“use factor”As overhead lines are exposed to all weathers, a continuing analysis is being made of the performance of lines, to assess whether they have been properly and rea sonably designed for the environment in which they are located. For many years, porcelain and glass were the only materials used for thb manufacture of insulators. These Insulators are still used for the vast majority of instal lations but a serious contender, referred to as 'composite insulators ' has appeared on the market and is siowy gaining acceptance. Composite insulators have many favourable mechanical characteristics, and they have aipeady- been used for the design of compact lines where they can become structural elements. Overhead transmission lines, by their very nature, are built across the countryside and are therefore subjec ted to climatic (meteorological) load influences, such as wind, ice and temperature, which can vary in time and in space. In addition, they can also be subjected to varying load influences due to geological effects, such as land slides-, subsidence, earthquake floods etc. A considerable amount of transmission and distribu tion especially in urban areas is carried out by means of underground cables. Even in sparsely populated reqions, high voltage bulk-transmission circuits have been placed underground where areas of outstanding natural beauty exist-, in some instances disused railway tunnels are being used for this purpose. A major problem in present-day technology is the development of cables which are not only economically more attractive but physically able to carry the very large powers in use and envisaged. The major cause of the lack of current carrying capacity in cables is the restriction on the temperature rise of the insulating material used with overhead lines this is by no means so severe a problem.-- xiiWhen designing cables it is necessary to take,> account of both aitibient conditions and the electrical stresses which may occur. Whereas the ambient conditions are important when selecting the right type of protective covering and armour, the electrical stresses are the > decisive factor for, amongst others, the thickness of the insulation and the right type of screen. The cables must be selected depending on rated- voltage, the requirements in operation and also economic considerations. A considerable development in recent years has been the widespread use of alüminlom as both a conductor and sheath material. It has largely superseded lead as a sheating material and is quickly gaining ground as a con ductor. A major problem with aluminium conductors has been the making of effective joints which are in practice subject to thermal cy ling and creep. Many techniques have been used and tioday much more confidence is placed in the available jointing techniques. At lower voltages ail-impregnated paper insulated cables (solid type) are used often with the three conduc tors contained in a single sheath. The theee conductors are stranded and insulated separately and then laid up spirally together. The space between and around the conductors is packed with paper or. jute to form a circular surface which is then further wrapped with insulation. This is called the belted type of cable. In mapy countries, for voltages above 33 kV, the type of cable system in most common use is the oil-filled cable with paper/oil insulation.' Ih the oil-filled ' cable the hollow centre of the conductor is filled with insulating oil-maintained under pressure by reservoirs feeding the cable along the route. At the highest voltages, at present of the order of 400 kVf the oil-filled cable has a design working stress of 150 kV/cm. The four main methods of installing cables are as follows: - Direct in the soil : the cable is laid in a trench which is refilled with a backfill consisting of either the original sou or imported material of lower thermal resistivity. - In ducts or troughs usually of earthenware or concrete : the cable is laid in open ducts which are some^ times filled with compound and covered with top slabs. - In circular ducts or pipes through ; this has the advantage of further cables being installed without excava tion. xiii- Where possible, cables are Installed in tunnels built for other purposes. Choice between overhead and underground depends upon a number of widely differing factors. Comparative economics (the annual cost of operation) is the most power ful factor influencing the choice. The capital cost of an underground system may be five to ten times that for an overhead system. Economically, conductors represent between 20 to 40 % of the total cost of a line, consequently their selection is of prime importance. Actually, the whole concept of electricity transmission or distribution revol*- ves around these elements. The economics of electric poweir transmission revolve around three topics t 1- The actual cost of transmitting unit energy over unit distance, 2- the relative transmission cost particularly as it varies between underground systems with respect to overhead lines, 3- the energy loss per umit energy transmitted over unit distance. To calculate the actual cost of power transmission, we have considered to the three major eostorcomponents which are a) the installed cost of transmission lines per unit length, b) the cost of the fixed energy losses (dieââctric, pumping, etc. ) c) the cost of the Joule losses, whic are proportional to the square of current or power fhow. Two types of annual cost (investment-related char ges and operating expenses) and also overhead expenses must be considered in an engineering economic study. Investment-related charges which are incurred by a utility are directly related to the capital investment. Operating expenses which include the labor and material costs for operating the plant involved. Maintenance expenses required to keep the system or plant in proper operating repair. Overhead expenses direct labor costs for personnel involved in the actual construction of a project or in the operation and maintenance of the completed plant. xivThe purpose of this thesis is to compare the costs of transmission between overhead lines a.nd under ground cables. For this purpose fixed and variable costs of both systems have been calculated as follows. The cost of the transmission system is ?Mk=Ms,k +Md,k (1) where M, = ' the cost of the line which has a, length of İ-. M,= the fixed annual cost. M?', = variable cost afhich depends on losses If the system has N cables, it would be written as k = 1,2,...,n. The total cost of the transmission system Is M = N M, (2) k =1 In this thesis for the conditions of Turkey an analysis example is given by using obtained equations. This analysis is based on 1989 prices and transmission models used in Turkey. TThe fixed annual cost and the cost of losses is calculated for both of the systems, for a given v, two different coltage levels (34,5 kV and 154 kV) and two different power factors (cos^j = 0,3 and cos = 0,9) the result related to the total cost is shown in Figure 1. M 154 kV Underground Overhead 154 kV 34,5 kV 34,5 kV Fig.l The total costs of transmission systems xvIt is apparent that overhead lines a.re cheaper than any underground cables, particularly at stable and high power factor loading, Where transmission distances are long and plenty of space is available, 'it is ' certain that overhead lines' must -be used* xv±
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