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Electrical Notes Pdf

Engineering Class handwritten notes, exam notes, previous year questions, PDF free download. Download Basic Electrical and Electronics Engineering Notes pdf. We have provided Basic Electrical and Electronics of medical-site.info 1st Year Study Materials and. All References are mention at end of each Notes. download All Electrical Notes & Calculation Sheets in PDF Format (US$) download All Electrical Notes & Calculation.

Electronic band theory a branch of physics said that a charge flows if states are available into which electrons can be excited. This allows electrons to gain energy and thereby move through a conductor such as a metal. If no such states are available, the material is an insulator. Most though not all, see Mott insulator insulators have a large band gap. This occurs because the "valence" band containing the highest energy electrons is full, and a large energy gap separates this band from the next band above it. There is always some voltage called the breakdown voltage that gives electrons enough energy to be excited into this band. Once this voltage is exceeded the material ceases being an insulator, and charge begins to pass through it. However, it is usually accompanied by physical or chemical changes that permanently degrade the material's insulating properties.

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In order to post comments, please make sure JavaScript and Cookies are enabled, and reload the page. Click here for instructions on how to enable JavaScript in your browser. Manoj Kumar September 29, at Vraj July 10, at Even a vacuum can suffer a sort of breakdown, but in this case the breakdown or vacuum arc involves charges ejected from the surface of metal electrodes rather than produced by the vacuum itself.

In addition, all insulators become conductors at very high temperatures as the thermal energy of the valence electrons is sufficient to put them in the conduction band. Wires sometimes don't use an insulating coating, just air, since a solid e. However, wires that touch each other produce cross connections, short circuits , and fire hazards. In coaxial cable the center conductor must be supported exactly in the middle of the hollow shield to prevent EM wave reflections.

Finally, wires that expose voltages higher than 60 V[ citation needed ] can cause human shock and electrocution hazards. Insulating coatings help to prevent all of these problems.

Insulator (electricity)

Some wires have a mechanical covering with no voltage rating[ citation needed ]—e. An insulated wire or cable has a voltage rating and a maximum conductor temperature rating. It may not have an ampacity current-carrying capacity rating, since this is dependent upon the surrounding environment e. In electronic systems, printed circuit boards are made from epoxy plastic and fibreglass. The nonconductive boards support layers of copper foil conductors. In electronic devices, the tiny and delicate active components are embedded within nonconductive epoxy or phenolic plastics, or within baked glass or ceramic coatings.

In microelectronic components such as transistors and ICs , the silicon material is normally a conductor because of doping, but it can easily be selectively transformed into a good insulator by the application of heat and oxygen. Oxidised silicon is quartz , i.

In high voltage systems containing transformers and capacitors , liquid insulator oil is the typical method used for preventing arcs. The oil replaces air in spaces that must support significant voltage without electrical breakdown. Other high voltage system insulation materials include ceramic or glass wire holders, gas, vacuum, and simply placing wires far enough apart to use air as insulation.

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Telegraph and power transmission insulators[ edit ] Power lines supported by ceramic pin-type insulators in California , USA Overhead conductors for high-voltage electric power transmission are bare, and are insulated by the surrounding air. Conductors for lower voltages in distribution may have some insulation but are often bare as well.

Insulating supports called insulators are required at the points where they are supported by utility poles or transmission towers. Insulators are also required where the wire enters buildings or electrical devices, such as transformers or circuit breakers , to insulate the wire from the case.

These hollow insulators with a conductor inside them are called bushings. 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. Recently, some electric utilities have begun converting to polymer composite materials for some types of insulators. These are typically composed of a central rod made of fibre reinforced plastic and an outer weathershed made of silicone rubber or ethylene propylene diene monomer rubber EPDM.

Composite insulators are less costly, lighter in weight, and have excellent hydrophobic capability. This combination makes them ideal for service in polluted areas.

However, these materials do not yet have the long-term proven service life of glass and porcelain. Design[ edit ] High voltage ceramic bushing during manufacture, before glazing.

The electrical breakdown of an insulator due to excessive voltage can occur in one of two ways: A puncture arc is a breakdown and conduction of the material of the insulator, causing an electric arc through the interior of the insulator.

The heat resulting from the arc usually damages the insulator irreparably. Puncture voltage is the voltage across the insulator when installed in its normal manner that causes a puncture arc. A flashover arc is a breakdown and conduction of the air around or along the surface of the insulator, causing an arc along the outside of the insulator.

Insulators are usually designed to withstand flashover without damage. Flashover voltage is the voltage that causes a flash-over arc. Most high voltage insulators are designed with a lower flashover voltage than puncture voltage, so they flash over before they puncture, to avoid damage.

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