Electrical insulating materials

Electrical insulating materials are materials that used to insulated the live wire,conductor in electrical cable,machine,transformers,motor etc.have high resistance to flow of current,less hygroscopic and long life.The properties of insulating materials have high dielectric strength,low dielectric losses,resistance to moisture ,high mechanical strength and good heat conductivity.According to physical state the insulating materials are gaseous, liquid, solid, fibrous, plastic,rubber,minerals,glass and porcelain.Gaseous insulating materials mostly used in high voltage applications.Air is important gaseous insulating materials used in cooling as well as insulation. Other gaseous insulating materials are hydrogen and sulfur fluoride use in generator cooling and HT circuit breakers respectively. Liquid insulating materials mostly used in transformers,HT circuit breakers and reactors.The insulating oil is used  as a cooling as well as insulation in transformers and HT switchgears for arc quenching at time of operation.Solid insulating materials are mica,paper,cotton and many more used in rewinding of electrical machines also found in liquid state and after solidify convert in to solid insulating materials.Varnish and drying oil are examples of solid insulating materials used to coating of super enamelled wire in rewinding electrical machines.Fibrous insulating materials mostly is textile materials like cotton and jute have mechanically strong,highly hygroscopic and cheap mainly used for cable manufacturing.Rubber,plastic and minerals insulating materials  mainly used for cable manufacturing plastic as a filler,rubber protect from moisture and minerals to provide high mechanical strength to the cable.Porcelain insulating materials are mainly used for overhead line insulation between pole and conductor.According to thermal classification solid insulating materials are
Class Y working temperature 90℃ used for small single phase machines and domestic appliances insulating materials are cotton, paper and silk not impregnated form.
Class A working temperature 105℃ used for rewinding of  AC and DC motors insulating materials are cotton, paper and silk impregnated form.
Class E working temperature 120℃ used for High voltage windings of transformers and induction motors insulating materials are cotton, paper laminated with formaldehyde bonding and epoxy resins.
Class B working temperature 130℃ used for manufacturing of welding machine insulation, DC machines commutator and salient pole alternator insulating materials are mica,asbestos and fiberglass.
Class F working temperature 155℃ used for lamination of machines insulating materials are silicone and heat resistance varnish.
Class H working temperature 180℃ used for high voltage transformer and slot lining of high voltage machines.
Class C working temperature 225℃ used for special purpose machine insulating materials are mica, glass,ceramics and quartz having high thermal stability.

Cotton Insulation

Cotton has low dielectric strength and hygroscopic.The insulating properties of cotton can be improved by applying insulating varnish.The application of cotton is rewinding of chokes,armature of small electrical machine,coils of small transformers and covering of bare wires.Empire cloth and black insulating tape are made when cotton impregnated with linseed oil and bitumen base varnish respectively.Silk is similar to cotton have higher tensile strength needs to impregnation with varnish or insulating oil.When cotton tape impregnated with bituminous compound called black tape used for protective braide of cables.If cotton tape coated with an insulating varnish known as empire tape are in black and yellow colour depends on varnish used.Due to high tensile strength,resistance to moisture and heat resistant used for HT and LT machines.
Wood a bamboo is used as an insulating materials in motor rewinding for supporting the coil in slots.The insulating properties of wood can be improved by impregnation with oil and varnish.

Rubber Insulation

Rubber is an insulating materials used as an insulation of cable.Natural rubber is vulcanised to make it suitable insulating materials, during vulcanisation sulphur is added to improve insulating properties.Rubber insulation tape is used for jointing rubber insulated cable.Hard vulcanised rubber are called ebonite is used for making of bushes,pins and terminal bases.It is available in sheets and rods.Paper is an insulating materials that can be used for providing insulation for power cable,rewinding of motors in slots and telephone cable.Ordinary paper have adequate insulating  properties can be further improved by addition of chemicals and varnishing during manufacturing
process. Chemically treated paper known as insulation board used for slot linear in electrical machine and transformer as spacers,washers and cylinders.

Paper Insulation

Mica insulating materials mostly used for high voltage generator and turbo generator.Mica have high temperature resistance,electric strength,mechanical strength and low dielectric loss.
Bakelite insulating materials used for main switches covers, terminal connectors and transformer cylinders mainly in plastic form.The bakelite sheets are made of cloth treated with phenolic resins and bonded in to homogeneous mass with heat and pressure.Such type of sheets available in black and brown depends upon varnish used.Paper  and fabric based bakelite available.

Glass insulating materials in brittle form used as a glass tape and varnished glass cloth.Glass varnished cloth used for insulating the high voltage machines working high temperature.
Insulating varnish is in liquid form.the main properties of insulating varnish have high chemical stability,air drying and not react with base materials.It is used for coating to fill voids in porous materials and motor windings to withstand the electrical and mechanical stresses better.Insulating varnish protects the windings against moisture,dirt,oils and chemicals,selection of suitable varnish depends on nature of winding wire insulation and thermal classification of insulation.

Mica Insulation

Insulating oil used in transformers as a insulation as well as cooling and oil type circuit breakers arc quenching at the time of making and breaking of contact.The insulating oil should be free
from moisture ,clean and high dielectric strength. The properties of transformers oil should be 40 Kv (r.m.s.)electric strength the gap will be 4mm between testing rods,specific gravity 0.85 to 0.88 and flash point min 145℃.If electric strength of transformer is low due to moisture and harmful

contaminants it is necessary treat in a filter plant before use in electrical equipment.
Polymers are also used as a electrical insulating materials. Some of the main polymers are Polyethylene,Polyisobutylene, Polyvinyl chloride,Polystyrene and Acrylic polymers.

Polyethylene commonly used for insulation of coaxial cables and moisture proofing because of high water resistant.

Polymer Insulation

Polyisobutylene used for cable coating have flexible and elastic nature.
Polyvinyl chloride is tough and plastic nature mostly used for cable jackets,fabric coating and lead wire insulation.
Polystyrene have high resistivity and  moisture resistant used to insulation of instrument panel.

Acrylic polymers mostly used for aircraft shields and having clarity and transparent.