Definition, Properties, and Physics of Insulators
– Electrical insulators are materials in which electric current does not flow freely.
– Insulators have tightly bound electrons that cannot readily move.
– Insulators have higher resistivity than semiconductors or conductors.
– Non-metals are the most common examples of insulators.
– Insulators become conductive when a sufficiently large voltage is applied, causing electrical breakdown.
– Electric charge flows when quantum states of matter are available for electrons to be excited.
– Insulators have a large band gap, which prevents charge flow.
– The breakdown voltage is the voltage at which insulators become conductive.
– Electrical breakdown is accompanied by physical or chemical changes that degrade the material.
– Insulators can become conductors at very high temperatures.
Uses and Applications of Insulators
– Insulated wire and cable are coated with an insulator to prevent cross connections and short circuits.
– Maximum voltage and conductor temperature ratings are important for insulated wire and cable.
– Printed circuit boards are made from nonconductive materials to support copper foil conductors.
– Active components in electronic devices are embedded within nonconductive materials.
– Liquid insulator oil is used in high voltage systems to prevent arcs.
– Overhead high-voltage electric power transmission conductors are insulated by the surrounding air.
– Insulating supports are required at the points where the conductors are supported by utility poles or transmission towers.
– Insulators are also required where wire enters buildings or electrical devices for insulation from the case.
– Insulators used for high-voltage power transmission are made from glass, porcelain, or composite polymer materials.
– Porcelain insulators are made from clay, quartz, or alumina and feldspar.
– Glass insulators have a higher dielectric strength but attract condensation and are difficult to cast without internal strains.
– Polymer composite materials are used for some types of insulators, offering cost-effectiveness and hydrophobic properties.
– Insulators can experience electrical breakdown through puncture arc or flashover arc.
– Puncture arc causes an electric arc through the interior of the insulator, damaging it irreparably.
– Flashover arc occurs along the surface of the insulator, usually without causing damage.
– High voltage insulators are designed with a lower flashover voltage than puncture voltage to avoid damage.
– Surface contamination like dirt, pollution, salt, and water can reduce flashover voltage and cause leakage currents and flashovers.
– Pin insulators, suspension insulators, strain insulators, post insulators, and composite insulators are different types of insulators.
Safety and Hazards
– Insulators prevent human shock and electrocution hazards.
– Cross connections and short circuits in wires can cause fire hazards.
– Insulation materials can prevent electrical corona and reduce wire vibration.
– Insulation in high voltage systems prevents electrical breakdown and arcing.
– Insulation materials are treated to have low flame spread and prevent current tracking.
– Class I insulation requires the metal body and other exposed metal parts of the device to be connected to earth via a grounding wire.
– Class I equipment needs an extra pin on the power plug for the grounding connection.
– Class II insulation means the device is double insulated.
– Double insulation requires both basic and supplementary insulation to prevent electric shock.
– Double insulated appliances are marked with a symbol of two squares in the EU.
Insulator Materials and Design
– Air is the most important insulation material.
– Wire coils in smaller transformers, generators, and motors are insulated with polymer varnish film.
– Thicker conductors may be wrapped with fiberglass insulating tape.
– Large power transformer windings are insulated with paper, wood, varnish, and mineral oil.
– Busbars and circuit breakers in switchgear may be insulated with glass-reinforced plastic.
– Porcelain insulators, glass insulators, and composite insulators are different types of insulator materials.
– Insulators can be designed as pin insulators, suspension insulators, strain insulators, post insulators, and composite insulators.
History and Miscellaneous
– Telegraph lines were the first to use insulators due to poor results with direct attachment.
– Glass insulators with unthreaded pinholes were used initially, required manual reseating.
– Ceramic insulators with threaded pinholes invented in the mid-1800s.
– Suspension-type insulators made high-voltage power transmission possible.
– Collectors’ organizations exist for insulator enthusiasts.
– Mast radiators require insulation from the ground, steatite mountings used.
– Guy wires supporting antenna masts have strain insulators to prevent short circuiting.
– Insulators placed in guy cables to prevent electrical resonances.
– Insulators are usually ceramic and cylindrical or egg-shaped.
– Arcing horns and lightning arresters necessary for protection against lightning strikes.
– Sheath insulator protects bottom-contact third rail in full length and is used in electrical systems for railways.
– Types of electric insulators include porcelain insulators, glass insulators, composite insulators, polymer insulators, and ceramic insulators.
– Applications of electric insulators include overhead power lines, substation equipment, transformers, high-voltage transmission lines, and electrical cables.
– Properties of electric insulators include high electrical resistance, low thermal conductivity, good dielectric strength, insensitivity to temperature changes, and resistance to chemical corrosion.
– Insulator testing and standards involve dielectric strength testing, insulation resistance testing, leakage current testing, and adherence to IEC 60137:2003 standard for insulated bushings.
– Insulator failure and maintenance are influenced by factors leading to insulator failure, contamination and pollution effects, and the importance of regular maintenance and inspection. Source: https://en.wikipedia.org/wiki/Electrical_insulation
An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and conductors—conduct electric current more easily. The property that distinguishes an insulator is its resistivity; insulators have higher resistivity than semiconductors or conductors. The most common examples are non-metals.
A perfect insulator does not exist because even insulators contain small numbers of mobile charges (charge carriers) which can carry current. In addition, all insulators become electrically conductive when a sufficiently large voltage is applied that the electric field tears electrons away from the atoms. This is known as electrical breakdown, and the voltage at which it occurs is called the breakdown voltage of an insulator. Some materials such as glass, paper and PTFE, which have high resistivity, are very good electrical insulators. A much larger class of materials, even though they may have lower bulk resistivity, are still good enough to prevent significant current from flowing at normally used voltages, and thus are employed as insulation for electrical wiring and cables. Examples include rubber-like polymers and most plastics which can be thermoset or thermoplastic in nature.
Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves. An insulating material used in bulk to wrap electrical cables or other equipment is called insulation. 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. They support the weight of the suspended wires without allowing the current to flow through the tower to ground.
