Transformer
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  • 1. TRANSFORMERWhat is Transformer?A transformer is a static electrical device that transfers energyby inductive coupling between its winding circuits. A varying current inthe primarywinding creates a varying magnetic flux in thetransformers core and thus a varying magnetic flux throughthe secondary winding. This varying magnetic flux induces avarying electromotive force (emf) or voltage in the secondary winding.Transformers range in size from thumbnail-sized used in microphones tounits weighing hundreds of tons interconnecting the power grid. A widerange of transformer designs are used in electronic and electric powerapplications. Transformers are essential forthe transmission, distribution, and utilization of electrical energy.The ideal transformer:Consider the ideal, lossless, perfectly-coupled transformer shown in thecircuit diagram at right having primary and secondary windings withNP and NS turns, respectively.
  • 2. The ideal transformer induces secondary voltage ES =VS as a proportionof the primary voltage VP = EP and respective winding turns as given bythe equation.- VP/VS = EP/ES = awhere,is the voltage ratio and NP/NS = a is the winding turns ratio, thevalue of these ratios being respectively higher and lower than unityfor step-down and step-up transformers,- VP designates source impressed voltage,- VS designates output voltage, and,- EP & ES designate respective emf induced voltages.Any load impedance connected to the ideal transformers secondarywinding causes current to flow without losses from primary to secondarycircuits, the resulting input and output apparent power therefore beingequal as given by the equationCombining the two equations yields the following ideal transformeridentityThis formula is a reasonable approximation for the typical commercialtransformer, with voltage ratio and winding turns ratio both beinginversely proportional to the corresponding current ratio.The load impedance is defined in terms of secondary circuit voltageand current as follows
  • 3. .The apparent impedance of this secondary circuit load referred to theprimary winding circuit is governed by a squared turn’s ratiomultiplication factor relationship derived as follows:APPLICATION OF TRANSFORMER:The most important uses and application of atransformer are:It can rise or lower the level of level of voltage or current(when voltage increases, current decreases and vice versabecause P=V*I, and power is same ) in an AC circuit.It can increase or decrease the value of capacitor, aninductor or resistance in an AC circuit. It can thus act as animpendence transferring device.It can used to prevent DC from passing from one circuit to throther.It can isolate two circuit electrically.Transformer is the main reason to transmit and distribute power inAC instead of DC, because Transformer not work on DCso there are too difficulties to transmit power in DC 9in the DCtransition and distribution the level of voltage step up by buck andboost converter but it is too costly and not suitable economically.In other word, increase or decrease the level of current, whilepower must be same other used and application of transformer.It step up the level of voltage at generation side beforetransmission and distribution in distribution side for commercial ordomestic use of electricity, transformer step down (decrease) thelevel of voltage for example from 11kV to 220V single phase and440 v three phase.
  • 4. The current transformer and potential transformer also used powersystem and in the industry also it is used for impendencematching.Pole mount distribution transformer with centre tapped secondarywinding used to provide split phase power for residential and lightcommercial service, which in Pakistan is typically rate 120/220 voltsource if image and attribution.Losses on Transformer:In a transformer there are different types of energy losses. The inputpower slightly differs from the output power. Transformers are made ofsoft iron core and insulated copper wires. They both have severalelectrical properties which causes power loss in a transformer. HowEnergy loss Occurs:Winding resistance:Current flowing through the windings causes resistive heating ofthe conductors. At higher frequencies, skin effect and proximityeffect create additional winding resistance and losses.Flux leakage:We know that magnetic flux is the fundamental thing behind theworking of a transformer. All the flux linked with the primary coilmay not cut the secondary coil. Thus energy losses in the form ofleaked flux. We have to think how to reduce the energy loss due toflux leakage? It can be done by minimizing the flux leakage. That’swhy in some efficient transformers, primary coil and secondary coil
  • 5. winds one over the other. Thus almost all the flux produced by theprimary coil will cut the secondary coil.Copper loss:Everyconductors, even super conductors have certain amount ofresistance. A transformer uses copper wires, which causes someenergy loss as heat. H=I^2RT.Eddy current losses:when conductors are subjected to change in magnetic flux,induced currents are produced in them like circular loops termedas eddy current. The alternating magnetic flux induces eddycurrent in the transformer core. Due to the resistance offered bythe iron core heat energy will create. This is the principle used inan induction cooker. Thus a large heat will generate at the core ofthe transformer. Eddy current losses can be lowered by usinglaminated cores.Hysteresis loss:some energy is losses as heat during the magnetizing anddemagnetising process of the core.Mechanical losses:In addition to magnetostriction, the alternating magnetic fieldcauses fluctuating electromagnetic forces between the primary andsecondary windings. These incite vibrations within nearbymetalwork, adding to the buzzing noise, and consuming a smallamount of power.