Competition Cracker for electrical engineers

This section is especially for preparation of competitive examinations based on previous blogs as discussed as under..................................👇
      
👉 SI Unit means (International System of unit) 
👉 Meter (m) is  the length equal to 1650763.73 wavelength in vacuum of the raditions corresponding to the transition between the level 2p10 and 5d5 of the krypton-86 atom.👉 Kilogram(kg) - The unit of mass and is equal to the mass of the international prototype of the kilogram.
👉 Second (s) - The duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine level of the ground state of caesium-133 atom.
👉 Ampere(A) -The constant current which ,if maintained in two straight parallel conductors of infinite length ,of negligible circular cross sectional ,and place one meter apart in vacuum ,would produce between these conductors a force equal to 2 X 10-7 newton per meter length.
👉 Kelvin (K) -It is the unit of thermodynamic temperature ,is the fraction 1/273.16of the thermodynamic temperature of the triple point of water.
👉 Candela (cd) -It the unit of luminous intensity ,in the perpendicular direction ,of a surface of 1/600000 square meter of black body at the temperature of freezing platinum under a pressure of 101325 newtons per square meter.
👉 Hertz (Hz) -The frequency of periodic phenomenon of which the periodic time is one second.👉 Newton(N)- Is that force which ,when applied to a body having a mass of one kilogram gives it an acceleration of one meter per second squared.
👉 Joule(J)- The work done when the point of application of a force of one newton is displaced through a distance of one meter in the direction of force.
👉 Watt(W)- It is the unit of power is equal to one joule per second.
👉 Coulomb (C)- The quantity of electricity transported in one second by a current of one ampere.👉 Volt (V) - The difference of electric potential between two points of a conducting wire carrying a constant current of one ampere ,when the power dissipated between these points is one watt.
👉 Farad (F)- The capacitance of an electric capacitor between the plates of which there appears a difference of electric potential of one volt when it is charged by a quantity of electricity by one coulomb.  
👉 Ohm (Ω)- The electric resistance between the two points of a conductor when a constant potential difference of one volt, applied between these points produces a current of one ampere in this conductor, provided no electromotive force is generated in the conductor.
👉 Weber(Wb)- The magnetic flux which linking a circuit of one turn ,produces in it an electromotive force of one volt as it is reduced to zero at a uniform rate in one second.
👉 Henery(H)- The inductance of closed circuit in which an emf of one volt is produced when the current in the circuit varies uniformly at the rate of one ampere per second.
👉 Lumen(lm)- The flux emitted within unit solid angle of one steradian of a point source having a uniform intensity of one candela.and Lux (lx) is an illumination of one lumen per square meter.👉 The copper have least resistivity (1.59 µohms/cm-cube) and graphite have higher resistivity (3000 µohms/cm-cube).
👉 The  mercury have least melting point (-38.86) and graphite have higher melting point (3500) in degree celsius.
👉 Resistivity depends on materials used in wire.
👉 Fuse wire should have high resistivity and low melting point.
👉 Resistivity of mercury at 4K is Zero.
👉 Two different wattage bulb connected in series then lower wattages bulb glows brighter vice versa in case of parller.
👉 The electric field inside a cylindrical conductor is zero when steady current passes through it. 
👉 Ohms law is applicable to all conductors of electricity.
👉 Kirchhoff's first law is based on the principle of law of conservation of charge and second law applicable for energy.
👉 EMF of a cell is a function of its resistance.
👉 Metals approach superconductivity near absolute zero temperature such type of metals are mercury and tin.
👉 Voltage dependent resistor usually made from silicon carbide used for suppress surges. 
👉 Variable resistor basically called a light dependent resistor.
👉 The value of conductance is high for good conductor of electricity.
👉 If we check open resistance through an ohm meter reads infinite.
👉 Thermistor has negative coefficient of resistance. 
👉 Production of heat due to current is related to Joule's law. 
👉 The conductivity is measure as mho/meter.
👉 Ohms law is not applicable for insulators and semiconductors.
👉 Lorentz method is used for measurement of absolute resistance.
👉 Heater coil glow but supply wiring does not glow because resistance  of heater coil is more than the supply wires.
👉 Filaments of electric bulbs are usually made of tungsten.
👉 The current carrying capacity of the fuse materials mainly depends on cross-sectional area,length and materials used.
👉 Mainly silver,copper and aluminium materials used as a fuse wire always installed in series circuit and rated as ampere.
👉 The individual components that make the circuit are called circuit elements.Two types of elements active and passive in a circuit.
👉 An energy source is an active element e.g. voltage,current sources.
👉 An element which store energy is called passive elements.
👉 Physically separate elements like R,L,C are called lump elements.
👉 A distributed element is inseparable for electrical purpose. In transmission line has R,L and C along its length and is a distributed element.near
👉 The elements which transmitted energy in either direction are called bilateral element while those allowing transfer of energy in one direction are called unilateral elements like diode,rectifier
👉When the output of an element is linearly related to its input,it is linear element otherwise it is a nonlinear element.
👉 Cloth dryer-100 Watt 
👉 Electric shaver-10 Watt
👉 Floor polisher-300 Watt
👉 Hair dryer-500 Watt
👉 Heating Pad-60 Watt
👉 Immersion Heater-700 and 1000 Watt
👉 Iron Automatic-1000 Watt
👉 Radio single circuit-30 Watt
👉 Rapid cooker-1200 to 1600 Watt
👉 Refrigerator-100 to 300 Watt
👉 Roaster-1500 Watt
👉 Television Set-100 to 200 Watt 
👉 Toaster-500 to 1000 Watt
👉 Vacuum cleaner-150 to 300 Watt
👉 Washing machine without elect. heater-300 Watt
👉 Washing machine with elect. heater-6300 Watt
👉 Water heaters 8 Litres-1200 to 2000 Watt
👉 Water heater 15 Litres-2000 to 4000 Watt
👉 Water heater 60 Litres-4000 to 6000 Watt
👉 Water heater  80 Litres-4000 to 6000 Watt

Transformers

TRANSFORMER

Transformer transfer alternating electrical power from one circuit to the other by the law of electromagnetic mutual induction without change in frequency.In this image V1 is AC primary voltage E1 and E2 is induced EMF in primary and secondary side respectively. The path of main flux Ø is laminated core of transformer. Transformer are two types step up and step down in step up transformer the primary winding have less number of turn compared to  secondary winding depending on the amount of voltage rise opposite in case of step down.Based on the winding connections transformer are three phase and single phase.The three phase high voltage step up transformer mostly used in generating station and industrial applications. Single phase low voltage step down transformer used for domestic purpose. The connection of three phase transformer mainly star/star,star/delta and delta/star.Scott connection used for phase transformation from three phase input power is transformed to two phase output power.Transformer consist of magnetic laminated core of soft iron the primary and secondary winding windings placed around it and transformer used only alternating voltage application.When AC voltage applied in primary winding EMF induced due to change in flux and also EMF induced in secondary winding by the law of electromagnetic mutual induction where the path of main flux is magnetic laminated core.If  secondary winding of transformer is close circuited iron and copper losses both the windings due to flow of current and induced flux. In other case secondary winding of transformer is open circuited secondary current is zero very small amount of exciting current drawn by the primary side and small amount of copper loss.Mainly primary side supplies iron losses in the core due to hysteresis and eddy current. Exciting current or no load current have two component one is active component that supplies iron loss and a small amount of copper loss in primary side of transformer and other reactive component produced flux not consumed any power when secondary is open circuited.Mainly transformer have two losses copper and iron.Copper loss occur due to resistance in windings and eddy current in the conductor is proportional to the square of the load current .Iron losses occur due to hysteresis and eddy current in the core are constant not depend on the load current. The efficiency of transformer is depend on the losses of transformer for more efficiency losses will be less.If the transformer efficiency measured over the period of 24 hours is called all day efficiency.In this case  calculating this efficiency energy output to the energy Input over a period of 24 hours.Such transformer design low flux density to reduce iron loss.The transformer have maximum efficiency when iron losses is equal to copper losses practically not possible.The main parts of transformer have a steel tank that consist of oil for cooling and insulation purpose, laminated core, primary and secondary windings.Conservator,Breather,Explosion vent pipe, thermometer and Buchholz relay all safety accessories mounted with tank for the operation of transformer. Conservator also known as expansion tank because transformer oil expand when hot and contract when cold it provide space for oil expansion and contraction it also perform minimises oxidation of  oil by limiting the surface area of oil in contact with air.Conservator connected with main oil tank through small pipe.Breather is a small container contains with silica gel which is blue in colour when dry and turns pink when it absorbed moisture reconditioned by heating and drying attached with one end of conservator tank. The function of breather absorb moisture air passing through it so that only dry air can enter to the tank breather also work as dehydrator.Explosion vent pipe simple like a bent pipe fitted on top of the main tank cover with a glass at the end.If any case insulation break down in side the transformer heavy short circuited excessive pressure build up inside the main tank a vent pipe provided protection against excessive pressure on account of the decomposition of oil so that main tank explode if vent pipe absence. Thermometer fitted in transformer winding so that observe the dangerous temperature rises and a temperature sensitive device for alarming sound. Thermometer also fitted for to indicate the oil temperature.Buchholz relay used in a transformer protection against low oil temperature connected between conservator and main tank. Two floats switch top and bottom provided and connecting to the relay for alarming sound  and trip circuit respectively.

SHORT CIRCUIT

OPEN CIRCUIT

Open circuit and short circuit test commonly conducted on transformers for iron losses and copper losses. In open circuit test one winding of transformer open and other connected to the supply of normal voltage and frequency.There will be no copper loss in open circuited winding watt meter reading will give the iron losses. In short circuit test low voltage winding short circuited and reduced voltage of sufficient magnitude applied high voltage side to circulate in the short circuit.The watt meter reading shows copper losses.The iron losses negligible during the test.Other tests of transformer are Ratio and polarity,Impedance test,Insulation resistance test,resistance of windings and core insulation voltage test etc.

AUTO TRANSFORMER

To improve voltage for domestic appliances and reduced voltage starters of three phase induction motor a auto transformer used. Such transformer has one winding act as primary and part of it as secondary for saving of copper cost compared to the two winding transformer.Main disadvantage of auto transformer is primary winding not insulated to secondary winding in case of fault the secondary winding energized to the high primary voltage. Booster transformer are used for raising line voltage when excessive voltage drop in the circuit.Current transformer and potential transformer are called instrument transformer used for measuring of large alternating current and large alternating voltage respectively.Current transformer are used for step down AC current from higher value to lower value for measurement with ammeter wattmeter,kwh meters etc.

PARALLEL OPERATION

The maximum load in volt ampere(VA) which may be applied across the secondary terminal without the ratio and phase angle exceeding the permissible limits is called burden of CT.Potential transformer step down the voltage connected directly to the power circuit between phase and ground.Volt ampere(VA) at a rated secondary voltage for a particular power factor called burden on potential transformer.Two or more transformer will operate in parallel satisfactorily, if they have voltage ratios,polarity, percentage impedance,phase sequence,vector diagram and phase displacement should be the same.    

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.

Importance of earthing in electrical technology.

Earthing is most important part of  the electrical technology that provides protection of personnel and equipments by the operation of the protective control gears like (ELCB) earth leakage circuit breakers and isolate the faulty circuit when insulation failure and accidental contact between high and low voltage.The earthing is the electrical connection between neutral or non current carrying electrical equipments part to the earth (Ground).The main part of the earthing is earth pit,earth electrode,connection wires and soil treatment materials like salt, charcoal etc.Earthing is two types system and equipment earthing. In system earthing the electrical connection between neutral and earth in generating station transformer used in power house.The heavy strip earth electrode use in mesh arrangements.The equipment earthing is electrical connection between non current carrying metal parts of electrical equipments and general mass of the earth like breakers,CT and PT etc. used in sub stations.In other word the earthing that restrict the voltage of live conductor with respect to the potential of earth.In practice there are three types of earthing method adopted a direct earthing system,earth neutral system and (ELCB) earth leakage circuit breakers system. In direct earthing system the all installation directly connected  to earth  not through the trip coil of the an earth leakage circuit breaker.In earth neutral earthing system the all installation connected  to earth in addition connected within the installation to the neutral conductor of the supply system.In (ELCB) earth leakage circuit breakers earthing system the part of an installation which are sought to be protected are connected to an earth electrode through the coil of ELCB which control the supply to that part of the installation also in addition to the equipement earth.The value of earth resistance kept low including earth electrode ,connection wire etc.for the operation of protective devices i.e. maintain the voltage between neutral and earth potential should be zero for good earthing, practically it is not possible due to  presence of some resistance.It is must to maintained low earth resistance when a circuit with large current carrying capacity is protected by a high capacity fuse. If the value of earth resistance is high than  the fault current not flowing to the earth cased fire as heating and arcing at point of high resistance which can set any inflammable object in the vicinity on fire.So in dry season to reduced the  resistivity of soil by pouring the water in earth electrode and maintain the moisture. The value of earth electrode resistance depends upon the electrical resistivity of soil in which the electrode is installed.The wet marshy soil,clayey or loamy mixed with small quantity of sand ,closely packed soil with fine grain and vegetation indicates soil with good moisture content is best for installation of earth electrode for getting low resistance path to flow of fault current.If moisture fall below 20% the resistivity of soil increases sharply so it is necessary to keep up the moisture level periodic addition of water.Where the soil is dry the artificial treatment of soil required done by adding of sodium chloride (common salt) calcium chloride and sodium chloride.The salt and charcoal added for the same purpose.The other method of treatment of soil by adding the chemical in soil.The material is suitable for earth electrode should be able to resist corrosion for a long time e.g. Galvanize iron,copper,and cast iron.Based on shape the earth electrode are Rod or Pipe, Strip and Plate. The minimum size of earth Rod electrode 16 mm for steel and 12.5mm for copper rod in 2.5meter in length.In case of pipe earthing electrode minimum inner dia 40mm for galvanize iron and 100mm for cast iron pipe in 2.5meter in length.In case of strip minimum cross sectional area for copper 20X3mm and 25X4mm for galvanize iron. When we used conductor for the earthing diameter 4mm(8 SWG) for copper and 6mm for galvanize iron.The length of buried conductor shall not be less than 15mtr.In case of plate electrode the minimum size of plate 60x60x3mm for copper and 60x60x6mm for iron and steel.Plate earthing is suitable for generating station.The driven electrodes earthing is suitable for soil free from stone , rock and undistributed soil so no excavation is necessary and cost of installation is low.Generally GI pipe are suitable for incomer breaker up to 200 ampere and GI plate earth electrode suitable for incomer breaker more than 200 ampere, neutral earthing of transformer as well as DG set up to 500 KVA.Copper plate earth electrode suitable for neutral earthing of transformer as well as DG set above 500 KVA. The size of earth bus 50mmX5mm of two copper strip in 11KV sub station and neutral of transformer, generator shall not be connected to this earth bus. The earth electrode fixed by welding ,bolting and clamped joints.All the surfaces where connections were made shall be free from grease,paint,dirt or any other foreign materials. All plugs and three pins sockets ,the earth pin connected to the earth wire.It is must to earthing of domestic appliances accepting those double insulation.The special earthing provided for data processing machine known as 'Clean Earth'. For protection against static charges such as hospital and operation theatres the static earthing suitable. The earth tester used for the measurement of earth resistance it contains three electrodes, one under measurement other two is potential electrode and  current electrode.The size of the potential  and current electrode is 15mm diameter  and length is 400mm long bars.The value of earth resistance should not more than two ohms another method to measure the earth resistance by voltmeter and ammeter method the electrode arrangement usually as the earth tester and find the earth resistance V/I reading shown in voltmeter and ammeter. The instrument used for measurement of resistivity contains four spikes two are current electrode and two are potential electrode driven into the ground at equal interval 'A' .The earth resistivity is given byρ=2ㄫAR where R is the steady reading on the instrument. The testing of insulation resistance between an insulated conductor and earth with the help of 500 volts megger. The phase conductor connected Line marked on megger and earth continuity conductor connected to an earth marked on megger.The handle is turned to indicate the steady reading on the instrument.The protection of all building and structure against lighting strokes like power house,large warehouses and monuments is done by installing lighting arresters at the top of the structure and connecting the same to the general mass of earth through a connecting conductor   and earth electrode so that the structure is not subjected to the dangerously high potential of the cloud discharge and system should be designed and maintained with low ground resistance.The conductor laid around the building near the top to the interconnected the various air termination called roof conductors protection against lightning strokes. The earthing system used for lighting protection must be independent of  the equipment earthing system. 

Jointing technique of power cable

When fault occurred in power cable like short circuit,ground and phase break in any reason required to repair by the process of jointing. In faulty power cable outer sheath and core insulation get damage.For jointing these power cable it is essential to adopt special technique and good quality insulating materials.Jointing also done when tap from main cable for service purpose and termination from transformers and other electrical equipments.The use of proper insulating materials depends on voltage rating of the power cable.For repairing of PVC insulated cable fabric and PVC tape used rated up to 6600 volts and impregnated paper tape suitable for 11kv and above.For repairing lead sheth lead tape and lead sleeve is suitable and armour is repair by using of copper flexible wire. Epoxy resin and bitumen used as a sealing compound protect from moisture.Bitumen compound is suitable up to 11kv and Oil resin compound suitable for 22 and 33Kv.The power cable mainly made up of aluminium and copper conductor, special technique used to jointing these cable. Aluminium conductor quite difficult to joint compared to copper conductor because presence of highly tenacious film of aluminium oxide is insulating in character and impairs the conductivity at joint. This film reforms in presence of air as soon as it is removed.We can joint the aluminium conductor by welding,soldering,compression and crimping of solderless lugs and in line connector. Welding is the best method of jointing the aluminium to aluminium conductor because electrically and mechanically stronger then the solder joints.In this method strip the insulation carefully without the scratches and cut in the conductor provide similar heat resistant such as asbestos,loose the conductor strand and clean the properly.Place the carbon mould  around the conductor and heat until it became red than weld the conductor strand together by puddling with an iron wire add more aluminium.Such type of method used to aluminium to aluminium conductor joint,straight joint and tee joints.Soldering method special types of solders fluxes used like tin,lead Zinc and Cadmium.Due to presence of highly tenacious film of aluminium oxide which prevents flow of solder between conductor strands by capillary action, while jointing the aluminium conductor by soldering method conductor should be proper cleaned for proper operation of fluxes.Temperature should be maintained around 300-350℃ at the time of jointing by using thermometer.All the accessories and conductor kept the same temperature and removed the dross formed on the surface of the solder should be removed.Straight through joints and tee joint should be done from this method.Compression and crimping of solderless lugs is the simplest method of jointing aluminium conductor.In this method suitable size lugs and In line connector used and crimp with manual crimping tools,hydraulic compressor tool with suitable die depend on the size of the cable.Uniform joint and no any special technique required in this method to prevents the chances of  Bi-metallic corrosion special metal alloy like zinc,tin,and silver coated sleeve is used. The advantage of jointing the conductor through this method having high electrical and mechanical strength. If aluminum conductor joint with other materials like copper due to presence of moisture corrosive chemical action takes place, So only tinned copper/brass connector should be used for bimetallic connections or joints and oxide inhibiting compounds should be used.Aluminium has also lower bending strength than copper therefore ,the conductor should be taken straight in to the connector or connected directly to the terminal lugs in the switchgear.The small aluminium conductors up to 4 sq mm in size may be formed in to an eye and connected to the post.  The jointing of copper conductor  is much easier than aluminum discussed previously.Soldering technique same as aluminum conductor for jointing copper conductor ordinary tin and lead solders are used and soldering flux removes oxide and prevents its formation during soldering ,so that the solder may  flow readily and result in proper jointing. The composition of tin and lead varies for the different application and temperature required accordingly.Example 60%(tin) and 40%(lead) is used for electronics applications at temperature 182-184℃.45%(tin) and 55%(lead) is used for sheet metal work at temperature 182-225℃ and 40%(tin) and 60%(lead) is used for plant applications at temperature 182-235℃. The outer insulation or protective sheathing of a cables to be repaired by insulating tape and vulcanizing process especially trailing cable used for give supply for portable and transportable electrical equipments.It is must to use same insulating materials  tape same as the core insulation.Such as paper insulated cable  a impregnated paper tape is suitable to repair, similarly PVC tape for PVC insulated cable and rubber tape for rubber insulated tape.While performing repairing work the surface should be properly clean on which the tape is to be applied tightly to exclude any air or moisture.First applied insulation tape then few layers of  waterproof empire tape finally friction adhesive tape as the finishing tape is called temporary repairing. In vulcanizing process we can repaired the rubber insulated cable joints are completely waterproof ,neat and good looking is called permanent repairing. Hot and cold vulcanizing process used the repairing of  outer sheathing of cable.In hot vulcanizing process vulcanizing machine used it is must to maintained the correct water level and 2 bar steam pressure otherwise machine  will burn out for completing a joint it will take  half or one hour depends on weather conditions. Jacket rubber and insulating rubber is suitable for repairing of outer sheath and core respectively.In cold vulcanizing process self vulcanizing tape used to repair outer insulation of the cable. Outer sheathing repair by using with patches.Patches should be six times larger than damaged rubber covering bevel rubber cover towards center of damage and brush of rubber scrapings after that apply vulcanizing fluid with clean brush and let it dry.Patches and stitch on the outer sheathing firmly from center towards edges with rollers.Other method of repairing outer rubber insulation by bandaging for rubber covering up to 2 mm used 35mm cable wrapping strip if rubber covering more thicker than 2 mm used 50 mm cable wrapping strip.In cold process bevel both ends of cut out approximate 30 mm inward with knife and brush of rubber scrapings thoroughly.Apply vulcanizing fluid with clean brush roughened area bandage inner rubber covering 25mm insulating rubber tape allowing no gapes.                  

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.                            

        

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.      

                   

Details to the capacitor, inductor and magnet.

Capacitor: This is a device that stored electrical energy for circuits initially power required. Capacitor consists of two conducting materials are separated by dielectric materials such as mica; paper etc. is the property of storing electrical energy known as capacitor or condenser but net charge in a capacitor is zero.  When voltage (V) applied to move electric charge (Q) in dielectric medium then Q ∝ V also written as Q=CV where Q charge in coulombs, V in volt, C in farads is called capacitance. Other units of capacitance are micro farads, pico farads and nano farads. We can define the farads when stored electrical energy increases by one coulombs and voltage changes at the rate of one volt per second is called one farads. Various type of capacitor based on dielectric materials paper, mica, ceramic and electrolyte capacitors. Charging the capacitor by battery connected across it and discharge by shorting the positive and negative each other. When the voltage applied in two conducting plates (V) and charged (Q) on the plates then stored energy in a capacitor is E=1/2 Q V or E=1/2 CV2 .DC capacitor used in electronics circuits for small voltages. AC capacitor used for low voltages applications such as ceiling fan, air cooler and air conditioner etc. and high voltages capacitors used for power factor improvement as we know current lead the voltage  in capacitor circuits at 90degree power factor maximum  called capacitor banks. The value of capacitance is directly proportional to the area of conducting materials (i.g. plate, wire, cylindrical) and inversely proportional to the distance between conducting materials separated by dielectric materials. (A) Capacitance between two plates C=K*ε0*A / d Farads where K is permittivity, ε0- epsilon naught the value is 8.854 X 10-12, A- area of plates sq. cm, d distance between two plates means thickness of dielectric in cm. (B) Capacitance between  more than two plates C=K*ε0*A(N-1) / d Farads. Permittivity is ability of a dielectric to store energy; we can also define energy stored per unit volume for unit potential gradient. This is unity for air and vacuum. The instrument used for measurement multimeter, Ammeter and voltmeter method and AC bridge method. Separate port provided to measurement of capacitance in multimeter discharge before used. In ammeter and voltmeter capacitance calculated C= 2 π f c v if voltage and current measurement through ammeter and voltmeter. In AC bridge two non inductive resistance, condenser under measurement and a standard condenser connected in bridge.

Construction of capacitor

Inductor: A coil of any conducting materials such as copper, aluminum called inductor. When inductor connected a power source due to this electric current flow a magnetic field developed. The energy is stored in a magnetic field as long as current flows, this magnetic field helps to store the electric current for a short time, even if the supply removed. We can say the capacitor stored electrical energy and inductor stored magnetic energy. When voltage applied in inductor (coil) due to change in current flux also change, change in flux EMF induced in it this is called inductance of coil. The direction of induced e m f opposes the flow of current, inductance is denoted by (L) and unit is Henry. One henry is define when 1volt is induced in a coil and current changes at the rate of  1amp per second. Various types of inductor are Fixed inductor, Iron core inductor, Air core inductor, Toroidal core inductor and Laminated core inductor. Fixed type inductor number of turns of the fixed coil remains the same used in electronics equipment such as radios. In iron core inductor conducting coil wound on iron core called ferromagnetic materials such as ferrite used higher frequency tuning .In Air core inductor conducting coil wound on non magnetic materials such as ceramic and plastic consider as air cored used as radios frequency. In toroidal core inductor conducting coil wound on magnetic core circular ring like iron powder used in AC electronics circuits application where high frequency and low power required. In Laminated core inductor conducting coil wound on thin steel sheet called soft iron piece used a low frequency suitable for transformer applications.

Construction of inductor

Magnet: In electrical magnet play an important role. Magnet is a body which attracts a piece of iron (magnetic material) place near it; have two poles one is the north another south pole. Opposite pole attracts each other and similar pole repel each other. There are two types of magnet permanent and electromagnet; permanent magnet also called natural used in alternator and other industrial applications but in case of electromagnet magnate  produced when current flowing in wingdings of motors placed around a  core of soft iron as long as supply given. Magnetic field is the area around a magnet within which it can attract a magnetic substance. Magnetic flux (φ) is a measurement of the total magnetic which passes through a given area. If a quantity soft iron materials placed around the current carrying conductor are arranged themselves in a definite patterns because of lines of force known as magnetic flux. This line of force travels from north to south outside the magnet and south to north within the magnet expressed as Maxwell. Flux density (B) is the flux (φ) per unit area Maxwell/sq.cm i.e. B= φ/A where φ=magnetic flux in Maxwell, A= area in sq.cm. Magneto motive Force (MMF) is the force which produces magnetic flux in magnetic circuits close similarity to electromotive force (EMF).MMF expressed as Gilberts and Ampere turns. MMF=0.4πNI. NI=Ampere turns. Magnetizing Force (H) is defined as MMF per unit length of path of the magnetic flux expressed as ampere turn per meter. Permeability is the ratio of flux density to the corresponding magnetizing force μ=B/H is unity for air and non magnetic materials. There are rules for electromagnets flaming right   hand rule finger pointing in the direction of current flow and the thumb will point the direction of North pole. The screw rule turn in the direction of current flow and travels in the direction of north pole. In case of AC generator Fleming right hand rules is applicable  thumb point direction of conductor motion forefinger direction of the flux and middle finger will point direction of induced EMF.

Construction of magnet

Details to the current and resistance and measurement.

Current: The flow of electrons in conducting loop called a current. Current denote as (I) and unit is ampere. Ampere is equal to the current that flow through a circuit of one ohm when one volt is applied across it.  As we know the electrons are negatively charged and direction flow from negatively point to positively point relatively and value is -1.6X10^-19 coulomb(C). Coulomb(C) is equal to quantity of electricity transferred in one second by a current of one ampere, It the unit for measurement of electricity quantity.   Two type current in circuits DC and AC. The flow of Direct current same at all points in time although an alternating current flow of charged electrons reverse direction periodically. The current free flow when the cross sectional area of the conductor more but less dense means current density inversely proportional to the area of conductor. When more area of the conductors current density less vice versa. We can define the current density the amount of electric current flow per unit cross sectional area of material. 

          Current density

Current density is the ratio of the current (I) flowing in a conductor to the cross sectional area (A) of that conductor expressed as J=I/A unit is Ampere/meter².

Skin effect 

The value of current density at high frequency  higher the outer surface of the conductor and lower at the center of the conductor called the skin effect. Due skin effect   transmission losses increased in high voltage transmission lines can be reduced by increase the voltage and reduce the current.

Ammeter

Ammeter is an instrument to measure the same current through a circuit. Ammeter is always connected series with the circuit if it is connected to parallel due to low resistance (few milli ohm) of ammeter cause short circuit and burn the ammeter.

Moving coil ammeter

Moving coil ammeter a movable coil placed in permanent magnate coil moved where current passing through it and pointer moved connected with moving coil used for DC current measurements.Moving iron ammeter a soft iron piece moves by the electromagnetic force of a fixed coil of wire used both AC and DC current. 

Moving iron ammeter

Moving magnet type meter a permanent magnet moves the pointer and coil is mounted on the meter. Electrodynamics type meter an electromagnet is used instead of permanent magnate to move the pointer. Hot wire type ammeter a current pass through a wire which expands as it heat cause move pointer.  For measuring of AC high current cannot pass through ammeter directly used current transformer (CT) or shunt.

Current transformer

Current transformer has primary and secondary windings, the secondary winding of CT always short circuited otherwise core saturation due to high voltage which can destroy the CT will be induced.  CT will reduce the current for measurement given to meter.

Clamp meter

Current can also measure by using clamp meter in this meter no any test lid needed. Such type of meter has a split soft iron core which placed around the conductor by pressing a trigger system and the change in magnetic flux which proportional value of current read directly on the digital scale. Such type of meter used both AC and DC measurement. In case of shunt ammeter high resistance alloy made up of manganin actually a milivoltmeter which is calibrated in ampere.

   Resistance: The flow of electrons resists by resistance it is different for different materials. The unit of resistance is ohm (Ω) and denoted by (R). Ohm is equal to the resistance offered to unvarying electric current by a column of mercury 106.3cm long having a cross sectional area of one sq.mm at the temperature of melting ice. We can also say an e m f of one volt will cause a current of one ampere through a resistance of one ohm. In any circuit value of resistance higher than then the voltage and power losses more. Conductance is opposite of resistance the unit of conductance is mhos (ʊ) and denoted by (Y).The resistance of conductor directly proportional to the length of the conductor and inversely proportional to the area of conductor. We can say when the length of conductor increases resistance should increase vice versa if area of conductor increases resistance should be decreases vice versa. In mathematical resistance is R=ρL/AL-length of the conductor in cm, R-resistance of the conductor, A- area of conductor sq. cm,ρ-resisitivity in cm cube. Conductance I=VY where I-current in ampere, V-voltage in volt, Y-Conductance mhos. We can define the resistivity with resistance formula ρ=R A / L i.e. resistance offered by any substance to flow of current per unit area per unit length known as resistivity. The symbol is rho ρ and unit ohms/cm. The resisitivity of aluminium conductor per sqr mm per meter length is 0.028 ohms and copper 0.018  ohms. Resistance can be measured by Ohmmeter, Comparison between two resistances,Wheatstone bridge,Post office Bridge, Voltmeter method etc.

Ohmmeter

Ohmmeter is an instrument used for measuring resistance directly a dry cell fitted as an energy source and galvanometer number of range with a suitable selector switch.Galvanometer calibrated to register ohms and before using the instrument checked resistance should be zero by touching two test prongs together.Start the measurement of resistance high range to right range reached otherwise instrument will be damaged.

Comparison of two resistance

Comparison between two resistances in this method comparison between two resistances one known and other unknown current passed through both the resistances and voltage drop measured across each and value of unknown resistance (R2) calculated in given image.

Wheatstone bridge 

Wheatstone bridge is a type of instrument to measuring resistance consist of two known resistances of fixed value one is veritable other to be measured. All resistances connected in bridge pattern.  Variable resistance adjusted such that no deflection on the galvanometer.In this method we can measured the resistance range between 1 ohm to 100 kilo ohm. The (R4) unknown resistance  ,R3 variable resistance ,R1 and R2 are known resistance.

Voltmeter 

Voltmeter method suitable for measuring high resistance a voltmeter known resistance is connected in series with the unknown resistance and known DC source applied across it . The formula of unknown resistance (R1) calculated where R is the meter resistance.