Details to the power,energy and introduction of cable

POWER: Power in electrical circuit work is done at the rate of one watt when an emf of one volt maintain a current of one ampere through a circuit of one Ohm resistance expressed in watt,kilo watt or mega watt.In direct current circuits power is P= I² X R=V² /R, Single phase AC circuit P=VI cosφ where cosφ  is  the power factor,Three phase circuit the power is P=3 V_ph I_ph cosφ  previously discussed. Watt is the electrical unit of power and mechanical unit of the power is "Horse Power" 1 Horse power (HP)=746 watt = 0.746 watt. Three types of power flowing AC circuits Apparent power known as kilo volt ampere(KVA) having two component one is the real power(KW)=apparent power(KVA)* cosφ other is reactive power (KVAR)= apparent power(KVA) * sinφ.Watt-meter  as an instrument that used to indicates the power in a circuits directly. The Watt-meter have current coil and potential coil . The current coil made in two part of thick wire connected in series and the potential coil or moving coil made of large number of turn of thin wire in series with a high resistance.The potential coil placed within the two sections of the current coil supported in jewel bearings. A watt-meter should be connected in the main circuit so that the moving coil end of the voltage coil and the series coil are on the same side of the load being measured.

Watt-meter

ENERGY: The total power consumed over a certain period of called energy expressed as "Kilo watt hours" Kwh. We can also say the power utilized at the rate of one kilo watt for one hour known as a unit energy.All tariff of electric energy consumption based of this unit. Energy is measured with the help of watt-hour meter either three phase three wire circuit or three phase four wire circuit for unbalance load.If the current is more than 100 Ampere connected the CT operated  KWH meter  such that placed around the current carrying conductor in certain ratio 200/5A i.e. 200 ampere flow in main circuits to be measured the 5 ampere in KWH meter.

CABLE: We can define the cable a length one or more than one insulated conductors which are laid up together are one core,two core, three core and  multi core.Conductor made up of either aluminium or copper,mainly aluminium conductor used  for manufacturing of power cable because light weight lower cost also due to shortage of copper in India.Some advantage to used copper conductor 100 percent conductivity lesser resistance per meter only (0.017241 ohm per meter) but aluminium have 60 percent conductivity and more resistance to copper (0.02245 ohm per meter).The selection of power cable depend upon its applications and insulation used. Different types of insulating materials used for meannufacturig of power cable are Impregnated paper,Rubber,PVC,Cross linked polyethylene(XLPE),Asbestos,Magnesium oxide,Glass,Quartz,Silicon Rubber etc.

Impregnated paper insulated cable have high electrical break down strength 40-50 KV/mtr. and long life but not moisture resistance operated temperature up 100 degree celsius.

Rubber insulated cable have moisture resistance,flexible and easy to handle but less operating temperature 70 degree celsius. 

PVC insulated cable dielectric strength and operating temperature same as rubber insulated cable but more tough, longer lasting and greater resistance to moisture acid,alkalies,fuels and oils than rubbers.  Cross linked polyethylene (XLPE) insulated cable have greater flexibility and high resistance to moisture operating temperature 90 degree celsius. Asbestos insulated cable  suitable for dry location absorbs moisture operating temperature range higher 100-200 degree celsius. Glass,quartz,silicon rubber insulated operating temperature above 150 degree celsius. 

Construction of cable: The conductor is covered by layer of semi conducting paper to smooth the  outer conductor surface than paper insulation and screen of metallised paper.The cores so formed are stranded together with jute or paper worming filling the interstices and wrapped with a binder of fabric tape interwoven with  copper and aluminium strands over the lead seath ,bedding,armouring and serving are provided.

SERVING:The protecting materials over the  wire armour of a cable  known as serving that will protect the cable against weather and  corrosion.The serving made of PVC,neoprene,glass tapes,paper cloths and jute etc.

BEDDING:Layers of impregnated fibrous materials applied to cable beneath the armouring to serve as a cushion like jute paper ,neoprene,glass,fiber tape etc.

Cable Construction

Protect from resistance to decay, abrasion moisture,acids,alkalies,protecting covering provided that depends upon the nature of the insulation and application of the cable.The protecting covering mainly are (A) Metal-Sheathing paper and rubber insulated cable  protect against moisture.(B) PVC- Sheathing protect against corrosive,acid and alkalies.(C) General and heavy duty natural rubber.

General and heavy duty polychloroprene protect from  heat,flame,oil and moisture.(D) Asbestos yarn protect from strong heat.

Protect from mechanical damaged steel wire and tape armour used applied  inn single and double layers.The wire armour should be preferred where cable are subjected to high tensile stress laid on sea-bed and deep shaft.