PRESENTATION ON: ELECTROMAGNETISM TOPIC: INSULATORS PRESENTED TO: DR. TARIQ BHATTI BSIT 3 RD SEMISTER BZU

GROUP MEMBERS NIMRA IRSHAD SADIA RASHEED 07-13

INSULATORS An insulator, also called a dielectric, is a material that resists the flow of electric current. Substances that have very high resistance, of the order of many megaohms are classified as insulators.

A material with atoms in which the electrons tend to stay in their own orbit is an insulator because it cannot conduct electricity very easily In insulators, all the electrons are bound with their respective atoms and cannot move freely Because electric current does not flow through them

Some solids e.g, wood diamond etc have very low conductivities ranging between and are called insulators

EXAMPLES OF INSULATORS WOOD PLASTIC GLASS

AIR VACUUM RUBBER MICA OIL DRY PAPER TEXTILE FIBERS

Moist earth is a fairly good conductor, while dry, sandy earth is an insulator Pure water is a good insulator but salt water is not

Types of insulators GLASS INSULATORS: Glass insulators were first produced in the 1850's for use with telegraph lines. As technology developed insulators were needed for telephone lines, electric power lines, and other applications.

In the mid 1960's a few people began collecting these antique insulators. Today there are over 2000 collectors. Insulator clubs, local and national shows, and good reference books are available

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PLASTIC INSULATORS Plastic insulators are made from a high-grade polypropylene or polyethylene material. They come in many sizes and shapes, to fit all types of permanent and temporary posts. Plastic insulators are not as long-lasting as porcelain

but they have quickly taken over the market due to their reasonable cost. Their only real 'enemy' is ultraviolet light, which causes them to become increasingly brittle with age

SOME OTHER FIGURES ARE SHOWN BELOW

RUBBER INSULATORS Rubber insulators consist of a wire-retaining flat strip that is mounted on a flat insulating rubber pad. The assembly is long enough to wrap half-way around a corner or end post. These rubber insulators are made to withstand the extreme pull of high- tensile wire

SOME OTHER RUBBER INSULATORS ARE SHOWN BELOW

PORECELAIN Fireproof and impervious to sunlight, porcelain insulators have been around the longest Porcelain is expensive, which is why they are being used less and less.

Porcelain insulators tend to develop tiny cracks ('crazing'), which fill up with soil and moisture. Crazing reduces the insulating quality.

ADVANTAGES OF INSULATORS Fiberglass is inexpensive as fiberglass is made from silica sand, an abundant resource. Fiberglass insulation does not burn or shrink. Fiberglass insulation also has good acoustic properties for sound absorption.

Fiberglass insulation has some environmental benefits as well The US Environmental Protection Agency requires all new fiberglass insulation to incorporate 20 percent recycled glass.

DISADVANTAGES OF INSULATORS  Does not stop radiant heat transfer  Potential health risks such as lung damage  Need an additional vapor barrier to protect it from moisture  Resistance to heat transfer drops dramatically when wet