Prof. Dr. Magdi El-Saadawi

Transcription

1 بسم هللا الرحمن الرحيم رب اشرح لى صدرى ويسر لى أمر واحلل عقدة من لسانى يفقهوا قولى صدق هللا العظيم Prof. Dr. Magdi M. El-Saadawi saadawi1@gmail.com 4/9/2017 Prof. Dr. Magdi El-Saadawi 1

2 Electrical Power (1) Course Code: EE /9/2017 Prof. Dr. Magdi El-Saadawi 2

3 Chapter 4 Components of Overhead Lines 4.1. Main Components of Overhead Lines 4.2. Conductor Materials 4.3. Line Supports 4.4. Insulators 4.5. Types of Insulators 4.6. Potential Distribution over Suspension Insulator String 4.7. String Efficiency 4.8. Methods of Improving String Efficiency 4.9. Points to keep in mind 3

4 Types of Towers p Suspension Towers 2- Tension Towers 3- Angle Towers 4- End Towers 4/9/2017 Prof. Dr. Magdi El-Saadawi 4

5 1- Suspension (Supporting) Towers Suspension straight towers are a type of selfsupporting tower that stands along straight sections of a transmission route. The only function of these types of towers is to suspend the wires. They do not have to create or regulate tension in any way. 4/9/2017 Prof. Dr. Magdi El-Saadawi 5

6 1- Suspension Tower 4/9/2017 Prof. Dr. Magdi El-Saadawi 6

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8 2- Tension Towers Tension towers are used to sectionalize the routes. They terminate the conductors and they provide containment of possible cascade failures. 4/9/2017 Prof. Dr. Magdi El-Saadawi 8

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10 2- Tension Towers 4/9/2017 Prof. Dr. Magdi El-Saadawi 10

11 2- Tension Towers 4/9/2017 Prof. Dr. Magdi El-Saadawi 11

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13 3- Angle Towers Angle towers are built when it is necessary for the route of the electrical current to turn. They are usually designed so that the axis of the cross-arm bisects the angle of the conductors. 4/9/2017 Prof. Dr. Magdi El-Saadawi 13

14 3- Angle Tower 4/9/2017 Prof. Dr. Magdi El-Saadawi 14

15 3- Angle Towers 4/9/2017 Prof. Dr. Magdi El-Saadawi 15

16 2- Terminal (End) Towers Terminal transmission towers are at the end of any route before connecting to a substation or to an underground cables in special cases They provide termination of the maximum conductor tensions. 4/9/2017 Prof. Dr. Magdi El-Saadawi 16

17 4- End Tower 4/9/2017 Prof. Dr. Magdi El-Saadawi 17

18 4- End Tower 4/9/2017 Prof. Dr. Magdi El-Saadawi 18

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20 Funny Towers 4/9/2017 Prof. Dr. Magdi El-Saadawi 20

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24 Bad Poles Nigeria 4/9/2017 Prof. Dr. Magdi El-Saadawi 24

25 Bangladesh 4/9/2017 Prof. Dr. Magdi El-Saadawi 25

26 India 4/9/2017 Prof. Dr. Magdi El-Saadawi 26

27 USA

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30 4.4 Insulators p. 99 They provide necessary insulation between line conductors and supports and thus prevent any leakage current from conductors to earth : They should have the following desirable properties: High mechanical strength in order to withstand conductor load, wind load etc. High electrical resistance of insulator material in order to avoid leakage currents to earth. High relative permittivity of insulator material in order that dielectric strength is high. The insulator material should be non-porous; free from impurities and cracks otherwise the permittivity will be lowered. High ratio of puncture ثقب strength to flashover. 4/9/2017 Prof. Dr. Magdi El-Saadawi 30

31 A. Porcelain Made of China Clay ) الصينى )الطين, Quartz, Alumina )سيليكات األلمنيوم(, and Feldspar )أكسيد األلمنيوم ) Electric strength is 60 kv/cm Advantages: high Mechanical strength Low leakage current Less affected by temperature and weather Disadvantages Heavier in weight More expensive Affected by air pollutants 4/9/2017 Prof. Dr. Magdi El-Saadawi 31

32 الزجاج المقس ى B. Toughened Glass Glass is cheaper than porcelain It has very high dielectric strength compared to porcelain. Electric Strength is 140 kv/cm It has lower coefficient of thermal expansion which reduces the strains due to temperature changes Moisture can easily condensed on glass surface and hence air dust will be deposited on the wed glass surface which will provide path to the leakage current of the system. For higher voltage glass can not be cast in irregular shapes since due to irregular cooling internal cooling internal strains are caused, so Glass insulators are used up to 33 kv lines. 4/9/2017 Prof. Dr. Magdi El-Saadawi 32

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34 C. Polymer Insulator A polymer insulator has two parts, one is glass fiber reinforced epoxy resin rod shaped core and other is silicone rubber or EPDM (Ethylene Propylene Diene Monomer) made weather sheds. Rod shaped core is covered by weather sheds. Polymer insulators rated from 69kV to 765kV 4/9/2017 Prof. Dr. Magdi El-Saadawi 34

35 الزجاج المقس ى B. Toughened Glass 4/9/2017 Prof. Dr. Magdi El-Saadawi 35

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37 4.5 Types of Insulators 1. Pin type insulators. 2. Suspension type insulators. 3. Strain insulators. 4. Shackle insulators. 4/9/2017 Prof. Dr. Magdi El-Saadawi 37

38 العوازل Pin type insulators المسمارية Pin type insulator consists of a single or multiple units. It is secured (تثبت) to the cross-arm on the pole. There is a groove on the upper end of the insulator for housing the conductor They are used only up to 33 kv. For higher voltages the pin type insulators are very heavy and more costly. 4/9/2017 Prof. Dr. Magdi El-Saadawi 38

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41 Single- unit pin insulator 11 kv Metal pin Double- unit pin insulator 33 kv Triple unit pin insulator > 33 kv 4/9/2017 Prof. Dr. Magdi El-Saadawi 41

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46 Causes of insulator failure: The electrical breakdown of the insulator can occur :ثقب or puncture وميض عابر either by flash-over In flashover, an arc occurs between the line conductor and insulator pin and the discharge jumps across the air gaps The insulator will continue to act in its proper capacity unless extreme heat produced by the arc destroys the insulator 4/9/2017 Prof. Dr. Magdi El-Saadawi 46

47 Causes of insulator failure: In case of puncture, the discharge occurs from conductor to pin through the body of the insulator. When such breakdown is involved, the insulator is permanently destroyed due to excessive heat. To avoid puncture by the line voltage: sufficient thickness of porcelain is provided in the insulator. 4/9/2017 Prof. Dr. Magdi El-Saadawi 47

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49 عوازل التعليق Suspension type insulators For high voltages (> 33 kv), it is a usual practice to use suspension type insulators Suspension insulator consists of a number of disc units mounted one above each other. Each disc is provided with a metal cap at the top and a metal pin under. A string of any number of units can be built according to the line operating voltage. The conductor is suspended below the point of support by means of insulator string 4/9/2017 Prof. Dr. Magdi El-Saadawi 49

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54 Insulator string 4/9/2017 Prof. Dr. Magdi El-Saadawi 54

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57 Advantages of Suspension insulators 1. Cheaper than pin type insulators for voltages beyond 33 kv. 2. Each unit or disc of suspension type insulator is designed for low voltage, usually 11 kv. Depending upon the working voltage, the desired number of discs can be connected in series. 3. If anyone disc is damaged, the whole string does not become useless. 4/9/2017 Prof. Dr. Magdi El-Saadawi 57

58 Advantages of Suspension insulators 4. They provides greater flexibility to the line. The insulator string is free to swing in any direction 5. In case of increased demand on the T.L, it is more satisfactory to supply the greater demand by raising the line voltage than to provide another set of conductors. The additional insulation required for the raised voltage can be easily obtained in the suspension arrangement by adding the desired number of discs. 6. They are generally used with steel towers. The arrangement provides partial protection from lightning. 4/9/2017 Prof. Dr. Magdi El-Saadawi 58

59 disadvantages of Suspension insulators 1. Suspension insulator string costlier than pin and post type insulator. 2. Suspension string requires more height of supporting structure than that for pin insulator to maintain same ground clearance of current conductor. 3. The amplitude of free swing of conductors is larger in suspension insulator system, hence, more spacing between conductors should be provided. 4/9/2017 Prof. Dr. Magdi El-Saadawi 59

60 عوازل األجهاد Strain insulators When there is a dead end of the line or there is corner or sharp curve, the line is subjected to greater tension. In order to relieve the line of excessive tension, strain insulators are used. They must have considerable mechanical strength as well as the necessary electrical insulating properties. For high voltage T.L, strain insulator consists of an assembly of suspension insulators. shown in Fig /9/2017 Prof. Dr. Magdi El-Saadawi 60

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62 عوازل األجهاد Strain insulators The discs of strain insulators are used in the vertical plane. When the tension in lines is exceedingly high, as at long river spans, two or more strings are used in parallel. They can be considered as special mechanical strong suspension insulators. 4/9/2017 Prof. Dr. Magdi El-Saadawi 62

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66 عوازل األصااد Shackle insulators In early days, the shackle insulators were used as strain insulators. Nowadays, they are frequently used for low voltage distribution lines. They can be used either in a horizontal or in a vertical position. They are directly fixed to the pole or to the cross arm with a bolt The conductor in the groove is fixed with a soft binding wire. 4/9/ Prof. Dr. Magdi El-Saadawi

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