02-03-2013, 02:45 PM
ELECTRICAL EVALUATION OF SILICONE RUBBER FOR HIGH VOLATGE COMPOSITE INSULATORS
ELECTRICAL EVALUATION.pptx (Size: 204.89 KB / Downloads: 28)
OBJECTIVE OF THE PROJECT
The main objective of this project is to evaluate special properties of silicone rubber used for manufacturing composite insulators. This includes analysis of silicone rubber of different manufacturers for ‘Hydrophobicity’ and ‘Resistance to Tracking and Erosion’.
Composite insulators are used in Transmission Lines and Railway Traction and are replacing conventional Porcelain and Glass insulators. Composite designs typically use engineered polymers which offer higher mechanical strength, greater design flexibility, reduced weight, lower breakage rates, superior dielectric strength, low leakage current and power loss, and excellent pollution performance than ceramic components.
What is an Insulator ?
An electrical insulator is a material whose internal electric charges do not flow freely, and which therefore does not conduct an electric current, under the influence of an electric field. A perfect insulator does not exist, but some materials such as glass and paper, which have high resistivity, are very good electrical insulators. Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. The term Insulator is also used more specifically to refer to insulating supports used to attach electric power distribution or transmission lines to utility poles and transmission towers.
Types of Insulator
Types of Insulators based on materials used:
Porcelain Insulators
Glass Insulators
Composite Insulators
PORCELAIN INSULATORS –
Porcelain insulators are made from clay, quartz or alumina and feldspar, and are covered with a smooth glaze to shed water. Insulators made from porcelain rich in alumina are used where high mechanical strength is a criterion. Porcelain has a dielectric strength of about 4-10 kV/mm.
GLASS INSULATORS –
Glass insulators were used to insulate lightning rods and cables from structures. Glass has a higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains. Glass of special compositions is used as an insulating material and annealing process to obtain high compressive strength toughens it.
COMPOSITE INSULATORS -
Polymer insulators essentially consist of a fibre glass core covered by weather sheds of silicone rubber and equipped with metal end fittings. It is also called Composite Insulators, which means it is made of at least two insulating parts – a core and housing equipped with end fittings. Composite insulators have many advantages over the ceramic and glass insulators such as good performance in contaminated environment, light weight, easy handling, maintenance free, and considerably low cost etc. Because of these properties it is gaining popularity worldwide and replacing the conventional ceramic and glass insulators.
Tensile Strength Test
Tensile strength test is used to evaluate the tensile (tension) properties of vulcanized thermo-set rubbers and thermoplastic elastomers. Through this test the ultimate tensile strength and percentage elongation are calculated to evaluate the flexibility of the Silicone Rubber used in the Composite Insulator.