رب اشرح لى صدرى ويسر لى أمر واحلل عقدة من لسانى يفقهوا قولى

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1 بسم هللا الرحمن الرحيم رب اشرح لى صدرى ويسر لى أمر واحلل عقدة من لسانى يفقهوا قولى صدق هللا العظيم

2 Chapter 11 Overhead Line Insulators pp

3 The insulators for overhead lines provide insulation to the power conductor from ground. They also carry the conductors The insulators are connected to the cross arm of the tower and the power conductor passes through the clamp of the insulator. 4/17/2013 Prof. Dr. Magdi El-Saadawi 3

4 Cross arm Insulator 4/17/2013 Prof. Dr. Magdi El-Saadawi 4

5 Characteristics of Solid Insulators 1. High Mechanical strength. 2. High Electric strength. 3. High insulation resistance.. )الشوائب والرطوبة ) moisture 4. Free from impurities and 5. Air and gas free (which decrease the dielectric strength) 6. Withstand the flashover phenomenon. 4/17/2013 Prof. Dr. Magdi El-Saadawi 5

6 Insulator Materials 1- Porcelain Made of China Clay ) الصينى )الطين, Quartz, Alumina ) األلمنيوم )أكسيد, and )سيليكات األلمنيوم( Feldspar Used with any number of units to increase the insulation level 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 4/17/2013 Prof. Dr. Magdi El-Saadawi 6

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10 Insulator Materials الزجاج المقس ى 2- Toughened Glass Glass is cheaper than porcelain Electric Strength is 140 kv/cm It has lower coefficient of thermal expansion which reduces the strains due to temperature changes Moisture condenses on the surface increases the leakage current Glass insulators are used up to 33 kv lines. 4/17/2013 Prof. Dr. Magdi El-Saadawi 10

11 Single unit Glass Insulator 4/17/2013 Prof. Dr. Magdi El-Saadawi 11

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20 Insulation Failure High Mechanical stress on insulator. Defects in insulator material (air, gases, impurities) Flashover of insulator (due to over voltages): The flashover voltage is the voltage which will cause an arc through the air surrounding the insulator. The arc heat can damage the insulator ( the insulators are fitted with arcing horns to keep the arc away from the insulator). Faults (short circuits) 4/17/2013 Prof. Dr. Magdi El-Saadawi 20

21 Types of Insulators 1- Pin Type Insulators ( المسمارية )العوازل p.371 Pin type insulator consists of a single or multiple units. They are used only up to 33 kv. For higher voltages the pin type insulators are very heavy and more costly. 4/17/2013 Prof. Dr. Magdi El-Saadawi 21

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23 Single- unit pin insulator 11 kv Metal pin Double- unit pin insulator 33 kv Triple unit pin insulator > 33 kv 4/17/2013 Prof. Dr. Magdi El-Saadawi 23

24 2- Suspension Insulators ( التعليق :(عوازل p.372 Suspension insulator consists of porcelain 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 4/17/2013 Prof. Dr. Magdi El-Saadawi 24

25 The number of discs in a string depends on the line voltage and the atmospheric conditions (degree of pollution). The usual number of discs are: Voltage (kv) : Number of discs: /17/2013 Prof. Dr. Magdi El-Saadawi 25

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28 Insulator disc (unit) Insulator string 4/17/2013 Prof. Dr. Magdi El-Saadawi 28

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31 3- Strain Insulators ( األجهاد (عوازل p375 These are special mechanical strong suspension insulators. They are used to take the tension of the conductors at the line terminals, at angle towers, and at road crossings. The strings are placed in horizontal plane. Two or three strings of insulators in parallel can be used when the tension in conductors is very high. 4/17/2013 Prof. Dr. Magdi El-Saadawi 31

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34 Arcing horns are used to protect insulators on high voltage Lines from damage during flashover. Over voltages on transmission lines, due to switching operations, lightning, or electrical faults can cause arcs across insulators (flashovers) that can damage them. The horns makes the flashover to occur between themselves rather than across the insulator surface. Horns are normally paired on either side of the insulator, one connected to the line and the other to ground. 4/17/2013 Prof. Dr. Magdi El-Saadawi 34

35 Arcing horn Strain Insulator with arcing horn 4/17/2013 Prof. Dr. Magdi El-Saadawi 35

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High Voltage Engineering

High Voltage Engineering Course Code: EE 2316 Prof. Dr. Magdi M. El-Saadawi www.saadawi1.net E-mail : saadawi1@gmail.com www.facebook.com/magdi.saadawi 1 Contents Chapter 1 Introduction to High Voltage