More about cables part-2

Vulcanized India Rubber

Some more other types of cable are vulcanized India rubber (VIR) cable insulated with natural rubber about up to 50 percent and rest other ingredients like sulphur, wax, carbon etc. by extrusion process and vulcanized. Such types of cable suitable up to 1.1kv grades.VIR insulated cable are basically braided and compounded ,Lead-alloy sheathed and Tough rubber sheathed. Braided and compounded cable is suitable for residential and industrial wiring. Lead-alloy sheathed cables suitable for damp locations and industrial wiring and not used in chemical plant and corrosive atmospheres.Tough rubber sheathed cable suitable for surface wiring in residential and industrial wiring. Weather proof cable provided with weather proof resistivity compound graded in 220/440 volts and 650/1100 volts.Fire-resisting cable is braided with asbestos yarn and is treated with a fire-resisting compound.Such types of cable used in automobiles and fire prone zone.

Polyvinyl chloride

PVC(Poly-vinyl-chloride) cable having high dielectric and mechanical strength good resistance to moisture,flame and fair resistance to acid,oils,fuels and corrosion used for laying on slopes and straight vertical.In four core cable three conductor having equal size and forth conductor neutral half of the others three distinguished in black colour and other three are Red, Yellow and Blue in colour.For identifying the cable, various conductor and insulating materials code used such as A-Aluminium conductor,P-Paper insulation,L-Lead sheath,LY-Lead alloy,S-serving,T-Double steel tape armor, W-Single wire armour,D-Double wire armour.We can identifying the cable code(APLSTS) as given on the cable is aluminium conductor,paper insulated,Lead sheath,double steel tape armour with serving over lead sheath and armour.

Mineral insulated cable

Mineral insulated cable copper/aluminium magnesium oxide used in their manufacture.Conductor is inclosed in an outer tube of the same metal (copper or aluminium) and the annular space is filled with magnesium oxide.Such type of cable have high operating temperature overload capacity and resistance to mechanical damaged.Special seal pots and watertight gland fittings are used for terminating these cables.

Silicone-Rubber cables consist of a seathing of silicone rubber protected with braiding of varnished glass thread,operating temperature is 180℃ for continuous and 250 ℃ for intermittent operation.Insulated winding wire known as magnet wire. Many types of winding or magnet wire for use for rewinding of electrical equipment such motor, alternator etc.Oil immersed appliances used in their manufacturing are paper,cotton,glass,PVC and synthetic enamels.Enamels insulated wire is used to form a magnet coil possesses excellent resistance to moisture ,abrasion,chemical and solvents.

Silicone-Rubber cables

The types of enamel wire are Annealed copper wire insulated by a film of natural resin and drying oil suitability to class A thermal classification called plain enamelled.Polyvinyl formal enamelled wire used up to 120℃ temperature and suitable for rewinding of motor,fan,transformer and high speed winding machine.Polyvinyl formal nylon enamelled wire having high resistance to abrasion not suitable for humid conditions because nylon affected by moisture suitability to class A thermal classification.Polyester enamelled wire is excellent thermal stability and flexibility temperature up to 155℃ suitability to class B thermal classification.Epoxy modified polyester wire is suitable to class F thermal classification available in golden colour used for rewinding of motor,transformer in damp location and chemical plants.

Magnet wire

Terephthalate polyester enamelled wire is suitable to class F thermal classification range up to 180℃ available in black colour.Polyurethane enamelled wire is suitable to class E thermal classification  available in transparent yellowish colour wide application in the field of electronics and telecommunication.Self bonding enamelled wire such type of wire thermoplastic poly vinyl top coat over a polyvinyl-formal or polyurethane as a base coat is suitable for class A thermal classification.The cable used to providing the supply for portable and transportable equipments known as trailing cable are greater flexibility.The installation of power cable either underground,open and over head.Advantages of installation  power cable in underground protect from rain storms and freedom from hazards of traffic mostly in substation and urban area but some disadvantage difficult to repair and cost is higher.Before the laying the power cable it is necessary to planning of soil condition such as temperature, thermal resistivity and presence of corrosive elements , moisture etc.The soil contains ashes,chloride salts,nitrates and alkaline materials should avoided for laying the cable.The cable not laid sites adjacent to the dc traction system.Now a days trench is dug in the ground and cable are laid on a bedding of sand and again covered with 10 to 12 cm of sand and protect with bricks or concrete slabs cable from mechanical damaged. Generally depth of trench depends on the voltage rating of the cable for 1.1 kv-0.45m,3.3kv-0.75m and 22 to 33kv- 1m and maintain the space between the cable 0.25 0.40 m in the same trench in order to reduced the effect of mutual heating.In road crossing underground cable cast-iron, galvanize-iron, stoneware or reinforced concrete pipe used to protect from mechanical damage and easier installation. For railway crossing cast-iron or spun-concrete pipes are used. It is necessary to maintain the clearance between the power and communication cable is 0.6m to avoid interference.It is necessary to record the value of resistance,capacitance and inductance and check the continuity, insulation resistance before laying  the power cable underground.Mostly the fault occurred in underground cable short circuit,ground fault between phases and any phase break due to any conditions.Current capacity of the cable depends on the size of the cable and type of installation air,duct trench and underground,some other factor like ambient temperature of air and soil.Thermal resistivity of soil for cables laid in ground also load factor and load cycle.Fuse and circuit breakers are device used for protection against short circuits operates after  lapse of certain time. Under short circuit condition conductor temperature rise for 11kv up to 160℃  22 and 33kv up to 120℃.The FT,FTD,P,PL and PC types of cable used in coal mines.FT type cable the tinned copper braiding used instead of wire armour for sake of extra flexibility. FTD type cable not present protective armoured suitable for electric drill.

XLPE 

P type cable stranded steel wire armour is provided for protection against mechanical damaged suitable for conveyor,loaders etc.PL type cable wire armoured provided for mechanical protection suitable for face lighting up to 250 Volts.PC type cable protected with armoured and sheathed with neoprene suitable for remote control equipment.The short time loading of the power cable is the time that cable utilize maximum current rating without exceeding the maximum permissible temperature of the conductor.The XLPE (cross linked polythene cable being used both HT and LT power distribution . The XLPE cable having higher power rating,emergency overload rating,short circuit rating,insulation resistance and moisture resistance.Lower installation cost due to less weight,longer life and resistance chemical and corrosive gasses.During a fire XLPE cable emits less smoke and corrosive gasses.