ELECTRICAL CABLE PREPARED BY : TUHIN HALDER & SURAJIT DUTTA

CABLE IS AN INSULATING CONDUCTOR, USED FOR TRANSPORTING ELECTRICAL POWER FROM ONE POINT TO OTHER

PRESENTATION ON CABLE CONTENT : History of cable Construction / Manufacturing Type of cable Cable selection Cable termination kit Financial viability

History of cable History of Paper Insulated Power Cables Early Cable Insulations Unvulcanized natural rubber – 1811 Glass tubes – 1816 Gutta-percha – 1841 (Morse, NYC) Vulcanized Natural Rubber – Goodyear patent –1844 (telelgraph cable in 1860) Parafined Jute & Vulcanized Bitumen – 1879 Natural rubber for power cables – 1880

Charecteristics of insulating material High insulation resistance High dielectric strength Good mechenical property Immune to attacks by acids & aikalies over a range of temp of about 18-94°c Non hygroscopic Non infiammable Low permittivity

Different type of cable insulation Gutta Percha Rubber VIR Varnished cambric Asbestos Silk & Cotton Enamel Impregnated paper Polyvinyl chloride Polythene Cross-Linked polythene

Comparison between Insulations NameResourceTemp. withstand Dielectric strength( kv/mm) Dielectric constant MeritsDemerits RubberNatural rubber from tropical treas, synthetic rubber from alcohol °c it absorbs moisture.2- soften when heated a tem 60-70°c VIRIt is prepared by mixing with sulphur,zinc oxide,red led etc. _ Non – hygroscopic, high elasticity & strength Due to sulphur contain it attacks copper.poor mechanical Property.

Impregn ated paper It is prepared from wood pulp rags by switable chemical process. 95°c High insulation resistivity, thermal conductivity. Hygroscopic. Polyviny l chloride This is synthytic compound,co ntained material known as plasticizer. 75°c 17 5It is inert to oxygen,oils & many alkalies & acids. _ Polythe ne It is a polymer derived from ethylene. 100°c _ lowHigh insulation resistivity& thermal dissipation property. _

Cross- Linked polythe ne Low density polythene vulcanised under controlled condition,res ults cross linked carbon atomes. 90°c 20 _High melting point,light weight,good mechanical strength. _ Varnishe d cambric It is a cotton cloth,coated with an insulating varnished. 85°c _ _ Asbesto s Silk & Cotton

Composition The materials are determined by three main factors: Working voltage, determining the thickness of the insulation; Current-carrying capacity, determining the cross- sectional size of the conductor(s); Environmental conditions such as temperature, water, chemical or sunlight exposure, and mechanical impact, determining the form and composition of the outer cable jacket.

Wire drawing PVC coating Twisting Final Sheath

construction of cables cores or conductors-made of tinned coppe or aluminium and are usually stranded. insulator-commonly used insulating materials are impregnated paper,varnishcambric or rubber. metallic sheath (lead,aluminium)-protect the cables from moisture,gases or other damaging liquid(acids,alkalies)in the soil and atmosphere. bedding(jute,hessain tape)-protect the metallic sheath againest corrosion. armouring(gaivanised steel,steel tape)-protect the cable from mechanical injury. serving(layer of fibrous material)-proect the armouring atmospheric condition.

construction of underground cable depends on two factores; insulating material voltage level

classification according to voltage lavel belted cable(up o 11kv) screened cable(from 22 to 66kv) pressure cable (beyond 66kv)

Belted cable construction core are insulated each othere by the layers of impregnated paper, paper belt of impregnated paper tape wound around the grouped insulated core. the gap between the insulated core is filled with fibrous insulaing material. the belt is covered with lead sheath.

disadvantages (when used beyond 22kv) tangential stress along layers of paper insulation leakage current the layers local heating risk of break down of insulation.

Screened cable (H-type,L-TYPE) H-type(construction) used upto 33kv,extended operating voltage 66kv each core is insulaed by the layer of impregnated paper. insulation of each coreis cover with a metallic screen,consists of a perforated aluminium foil. cores are laid in such a way that matallic screen contact with one another. each core screen is in electrical contact with conducting belt and lead sheath. advantages electric stresses are purely radial reduce dielectric loss. air pockets or voids in the dielectric is eleminated.