Çok yüksek gerilimli enerji iletim hatlarının planlanmasında ve optimal işletilmesinde etkili korona kayıpları
Corona losses affecting design and optimal operation of extra high voltage transmission lines
- Tez No: 21732
- Danışmanlar: PROF. DR. NESRİN TARKAN
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 112
Özet
ÖZET Bir yüksek gerilim iletim şebekesi planlama ve tasarlamanın esas amacı, elektrik enerjisini en düşük maliyette ve yeterli güvenilirlikle iletmektir. Bu nedenle, çok yüksek gerilim hatlarının tasarlanmasında göz önünde tutulacak belli başlı faktörlerden biri de korona ve kayıplardır. Bu tez çalışmasının amacı, çok yüksek gerilim enerji iletim hatlarında meydana gelen korona kayıplarını incelemektir. Bu yüzden, önce iletim sistemi planlama çalışmalarında dikkate alınması gereken faktörler sıralanmış, korona kayıplarının şebeke kayıplarındaki yeri belirtilmiştir. Üçüncü bölümde, korona kavramı, korona olayının belirtileri ve koronaya etki eden faktörler üzerinde durulmuş, korona kaybı hesaplarında kullanılan gerekli formüller açıklanmıştır. Ayrıca Peterson 'a göre simetrik olmayan belli bir hat durumu için korona kayıp incelemesi yapılmış, gerekli grafikler elde edilmiştir. Daha sonra korona güç kayıplarında azaltıcı rol oynayan ve daha fazla güç iletilmesine yol açan demet iletkenler açıklanarak, demet iletkenli durumda hat kapasitesine etki eden etkenler anlatılmıştır. Dördüncü bölümde, korona kayıplarının saptanmasında kullanılan olasılık yöntemi gerekli formüller, tablolar, grafikler ve örnek hesaplamalarla verilmiştir. Bu yöntemle, açık ve kötü hava durumu için ortalama yıllık kayıp ve üç fazlı hattın maksimum kayıp değerlerinin de hesaplanabildiği görülmüştür.
Özet (Çeviri)
SUMMARY CORONA LOSSES AFFECTING DESIGN AND OPTIMAL OPERATION OF EXTRA HIGH VOLTAGE TRANSMISSION LINES Its greatest advantage is that electric energy is very easily transmittable and convertible to other forms of energy. In almost every country, it is now being utilized in everyday life at an ever-increasing rate. The average annual consumption of electric energy per capita is a recognized criterion for a country's degree of technical development and standart of living. The annual rate of increase in electric energy consumption in North America and Europe is now about 2 to 4%. In developing countries the rate is much higher. To meet the ever-increasing demand for electricity, larger and larger power stations are being planned, built and commissioned for efficient utilization of water power, conventional fuel, and nuclear fuel. It is now quite common to find 1000 MW being generated in a single power station. Such power stations are designed to be appropriately located in terms of fuel handling and cooling-water supply, often at long distances from areas of concentrated electricity consumption. The heavier the power to be transmitted and the longer the transmission distance, the higher the line voltage will have to be. This is determined by several technical and economical factors, including efficiency, voltage drop, system stability, and number of circuits necessary for a secure supply of energy. For example, to transmit 10-100 GW of power over a distance of about 500 km, the suitable line voltage could be either 750 kV ac or ± 600 kV dc. Therefore, with the ever-growing need to transmit greater amounts of power longer distances, transmission lines with higher and higher voltages have been built in many countries over the years. Figure 1 shows the world record voltages for ac and dc lines. Ultrahigh voltage (ÜHV) of about 1500 kV ac may be in service before long. VIumax.kv 1800 1600 U00 1200 1000-j 800 600 400- 200- U.5.A. U.S.S.R. i DC- ! Brazil J. Mozambique p- U.S.S.R. Canada r1 USA, Canada riU-SA. i U.S.5.R.I-J j i New Zealand i England Svw?den - I France 1900 1920 1940 - I r 1960 - I 1 T ' 1980 2000 Year Fig. 1 The highest voltage used for ac and dc transmission in the world, showing the increase over time. The dc voltages are between the poles of bipolar lines. In certain situations it may be preferable to use dc rather than ac for power transmission. DC transmission lines are more economical to build, suffer fewer voltage drops and losses, are most suitable for interconnecting asynchronous networks, and do not impose an extra burden on the switchgear of connected ac networks. On the other hand, they do not carry reactive power, and their terminal inverter stations produce harmonics that have to be carefully filtered. The function of the overhead three-phase electric power transmission line is to transmit bulk power to load centers and large industrial users beyond the primary distribution lines. A given transmission system comprises all land, conversion structures, and equipment at a primary source of supply, including lines, switching, the conversion stations, between a generating or receiving point and a load center or wholesale point. The decision to build a transmission system results from system planning studies to determine how best to meet VXlthe system requirements. At this stage, the following factors need to be considered and established: 1. Voltage level. 2. Conductor type and size. 3. Line regulation and voltage control. 4. Corona and losses. 5. Proper load flow and system stability. 6. System protection. 7. Grounding. 8. Insulation coordination. 9. Mechanical design: a. Sag and stress calculations. b. Conductor composition. c. Conductor spacing. d. Insulator and conductor hardware selection. 10. Structural design: a. Structure types. b. Stress calculations. The basic configuration selection depends on many interrelated factors, including the esthetic considerations, economics, performance criteria, company policies and practice, line profile, right-of-way restrictions, preferred materials, and construction techniques. Corona discharges form at the surface of a transmission-line conductor when the electric-field intensity on the conductor surface exceeds the breakdown strength of air. Corona manifests itself by bluish tufts or streamers appearing around the conductor, being more or less concentrated at irregularities on the conductor surface. This discharge is accompanied by a hissing sound and by the odor of ozone. In the presence of moisture, nitrous acid is produced. Corona is due to ionization of the air. The ions are repelled from and attracted to the conductor at high velocity, producing other ions by collision. The ionized air is a conductor (however, of high resistance) and increases the effective diameter of the metallic conductor. Corona on transmission lines causes power loss and radio and television interference. Corona loss is probably the most difficult item which the transmission engineer is viiicalled upon to determine. It is affected by many things: conductor diameter, number of conductors per phase, phase spacing, conductor surface condition, weather, altitude, temperature, and voltage. Corona loss and its economic consequences have been a subject of study for over half a century. Much useful laboratory and field data have been collected, laws of corona formulated, and the problem investigated in many of its theoretical aspects. Yet, with the advent of construction of ehv lines, it was still not possible to predict with any degree of confidence either the corona- loss characteristics that these lines would exhibit or the economic aspects of different choices of conductor to compensate for these losses. Therefore, corona-loss studies have been included in most of the ehv research projects initiated in recent years. The results of these studies comprise large quantities of statistical data on corona loss as a function of conductor geometries, conductor gradients, voltages, and the meteorological conditions to which lines are subjected. It has been found, for example, that corona loss on an ehv line can fluctuate from a few kilowatts per km in fair weather to as much as several hundred kilowatts per km in rain or snow. The average corona loss was found to be only a small portion of the I2R losses, but the peak losses have been viewed as having a significant influence on demand requirements, since generation must be provided to meet this peak or additional energy imported to supply it. Therefore, the probability of peak corona losses coinciding with peak-load requirements needs to be clearly defined for any proposed line design, otherwise the line designer has no basis to evaluate effects of conductor or voltage changes on corona-loss economics. Statistical data provided on corona-loss research in recent years permit a description of the losses that a line will experience on both an energy and a demand basis; thus, more optimized designs are now possible. Corona-loss measurements have been an important part of the research performed at Project UHV. It has been noted however that, as transmission voltage levels increase, corona loss plays a diminishing role in the selection of conductor size and line geometry. Conductor IXdesign for ultrahigh voltages will be determined more by audible and radio noise than by corona-loss requirements. In general, if corona loss is expressed as a percentage of the surge impedance load of the line, a uhv line designed for acceptable audible and radio-noise performance will experience less foul-weather corona loss than ehv lines. In addition to this, the ratio of fair-weather loss to foul-weather loss will also be lower for uhv lines, with the result that fair-weather loss will be insignificant for practical aims. The purpose of this thesis is to examine corona power losses on extra high voltage transmission lines. In this thesis, Peek's and Peterson's formulas are used to calculate corona losses. Apart from these a probabilistic method is utilized to determine the corona losses on the extra high voltage of various standart designs.
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