Insulators

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insulators,pin type,suspension type,strain type,shackle type,stay type

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Insulators: 

Properties – Mechanically Strong High insulation Resistance Free from internal impurities High Dielectric Strength High relative permittivity Non porous Should not get affected with changes in temperature Insulators 11/10/2012 1

PowerPoint Presentation: 

11/10/2012 2

Insulator Materials: 

Porcelain Glass Synthetic resin Insulator Materials 11/10/2012 3

Porcelain: 

Manufactured from China Clay Plastic clay is mixed with silicon and feldspar and processed in the mills. It is heated at the controlled temperature. Given a particular shape and covered with glaze. Galvanized Cast iron is used for metal parts inside. Insulation resistance is high. Porcelain is heated to temperatures such that insulators become mechanically strong and remains non porous. As it is glazed remains clean from dust and moisture. Dielectric Strength is about 60kV/cm. Porcelain 11/10/2012 4

Glass: 

Glass is made tough by heat treatment – Annealing. As transparent cracks, bubbles and any defects can be easily detected. Di electric strength is high. Low Coefficient of thermal expansion – less affected by changes in temperature Cheaper than porcelain Resistivity is high Simple design Less stronger than Porcelain Cannot be moulded in regular shapes Glass 11/10/2012 5

Synthetic Resin: 

Compounds of silicon, rubber, resin. High tensile strength Low weight Comparatively cheaper High leakage current Short life span Synthetic Resin 11/10/2012 6

Types of Insulators: 

Pin type Insulator Suspension type Insulator Strain Insulator Shackle Insulator Stay Insulator Types of Insulators 11/10/2012 7

Pin type Insulator: 

Pin type Insulator 11kV Pin type Insulator 22 kV Pin type Insulator 11/10/2012 8

PowerPoint Presentation: 

Each pin piece – 11kV Used for 11kV, 22kV, 33kV. Beyond this Uneconomical Upper end groove is provided to hold the Conductor Connected to cross arm with the help of steel bolts To avoid direct contact of hard metal with porcelain lead screws are used. Used in the transmission lines running straight. The conductor passes through the groove on the upper end and is bound by the binding wire of soft copper or soft aluminum. 11/10/2012 9

Suspension type insulator: 

Suspension type insulator 11/10/2012 10

PowerPoint Presentation: 

It has number of porcelain disc units which are connected in series with the help of metal links. Top most insulator is connected to the cross arm where the bottom most unit holds the line conductor through the conductor shoe. Each disc is designed for a voltage of 11kV. Consist of disc shaped piece of porcelain grooved at the bottom. Galvanized cast iron cap is provided at the top with a hole to hold the pin of other unit. Cap and pin are cemented to the insulator E xpansion of cement, iron & porcelain cracks can form – failure. For Higher voltages cheaper than pin insulators. In case of failure replacement work is easy As string is suspended free to swing in any direction. Takes position that mechanical stress is minimum 11/10/2012 11

Strain Insulators: 

Strain Insulators 11/10/2012 12

PowerPoint Presentation: 

Used in the dead end or corner or while crossing the river. These reduces the excessive tension on the line. Assembly is similar to suspension insulators Discs are in vertical plain instead of horizontal plain in suspension insulators. During river crossing there will be excessive tension in the line. Hence 2 or more strings of insulators are used in parallel. 11/10/2012 13

Shackle Insulators: 

Shackle Insulators 11/10/2012 14

PowerPoint Presentation: 

Also called Spool Insulators Used for low voltage distribution lines. Can be used in horizontal or vertical position. Used at the dead end of aerial wire of service connection to a house or a factory where there is excessive mechanical stress on the line. It has a through hole in the center for the bolting purpose. On each side of the insulator there is galvanized iron plate. Other end of the plate is placed around the cross arm of the pole. 11/10/2012 15

Stay Insulators: 

Stay Insulators 11/10/2012 16

PowerPoint Presentation: 

They are also called Egg Insulators In case of low voltage lines, it is necessary that the lines are to be insulated at a height of not less than 3 meters from ground. Stay insulators are used on the wire to create insulation between pole and stay clamp. Made up of porcelain It has two holes for the stay wires and the design is such that in case of insulator breakdown, stay wire will not fall on the ground. 11/10/2012 17