DASMESH PARIVARINTERNATIONAL SCHOOL PROJECT REPORT ON TRANSFORMERS Submitted By: TANUJ GUPTA CLASS: XII ROLL NO: ________________
They are so important in our livesthat without them even the electricbells fitted in our homes won’twork.
CertificateThis is to certify that Tanuj Gupta, student of Class XII, Dasmesh Parivar InternationalSchool, has completed the project titled Transformers during the academic year 2012-2013 towards partial fulfillment of credit for the Physics practical evaluation of CBSE2013, and submitted satisfactory report, as compiled in the following pages, under mysupervision._________________Department of PhysicsDasmesh Parivar International School
Acknowledgements"There are times when silence speaks so much more loudly than words of praise toonly as good as belittle a person, whose words do not express, but only put aveneer over true feelings, which are of gratitude at this point of time."I would like to express my sincere gratitude to my physics mentor for his vitalsupport, guidance and encouragement, without which this project would nothave come forth. I would also like to express my gratitude to the staff of theDepartment of Physics at Dasmesh Parivar International School for their supportduring the making of this project. TANUJ GUPTA
INTRODUCTIONThe transformer is a device used for converting alow alternating voltage to a high alternatingvoltage or a high alternating voltage into a lowalternating voltage. It is a static electrical devicethat transfers energy by inductive couplingbetween its winding circuits. Transformers range insize from a thumbnail-sized coupling transformerhidden inside a stage microphone to huge unitsweighing hundreds of tons used in power plantsubstations or to interconnect portions of thepower grid. All operate on the same basicprinciples, although the range of designs is wide.While new technologies have eliminated the needfor transformers in some electronic circuits,transformers are still found in many electronicdevices. Transformers are essential for high-voltage electric power transmission, which makeslong-distance transmission economically practical.A transformer is most widely used device in bothlow and high current circuit. In a transformer, theelectrical energy transfer from one circuit toanother circuit takes place without the use ofmoving parts. A transformer which increases thevoltages is called a step-up transformer. A
transformer which decreases the A.C. voltages iscalled a step-down transformer. Transformer is, therefore, an essentialpiece of apparatus both for high and low currentcircuits. Close-up of single-phase pole mount transformer.
PRINCIPLEIt is based on the principle of mutual induction thatis if a varying current is set-up in a circuit theninduced e.m.f. is produced in the neighboringcircuit. The varying current in a circuit producevarying magnetic flux which induces e.m.f. in theneighboring circuit.
CONSTRUCTIONA transformer consists of a rectangular shaft ironcore made of laminated sheets, well insulated fromone another. Two coils p1 & p2 and s1 & s2 arewound on the same core, but are well insulatedwith each other. Note that the both the coils areinsulated from the core, the source of alternatinge.m.f is connected to p1p2, the primary coil and aload resistance R is connected to s1 s2, thesecondary coil through an open switch S. thusthere can be no current through the sec. coil solong as the switch is open. For an idealtransformer, we assume that the resistance of theprimary & secondary winding is negligible. Further,the energy loses due to magnetic the iron core isalso negligible. For operation at low frequency, wemay have a soft iron. The soft iron core isinsulating by joining thin iron strips coated withvarnish to insulate them to reduce energy losses
by eddy currents. The input circuit is calledprimary. And the output circuit is called secondary. An ideal voltage step-down transformer. The secondary current arises from the action of the secondary EMF on the (not shown) load impedance. The ideal transformer as a circuit element
THEORY AND WORKINGWhen an altering e.m.f. is supplied to the primarycoil p1p2, an alternating current starts falling in it.The altering current in the primary produces achanging magnetic flux, which induces alteringvoltage in the primary as well as in the secondary.In a good-transformer, whole of the magnetic fluxlinked with primary is also linked with thesecondary, and then the induced e.m.f. induced ineach turn of the secondary is equal to that inducedin each turn of the primary. Thus if Ep and Es bethe instantaneous values of the e.m.f.’s induced inthe primary and the secondary and Np and Ns arethe no. of turns of the primary secondary coils ofthe transformer and, Dфь / dt = rate of change offlux in each turn of the coil at this instant, we haveEp = -Np Dфь/dt (1)
Es = -Ns Dфь/dt (2)Since the above relations are true at every instant,so by dividing 2 by 1, we get Es / Ep = - Ns / Np (3)As Ep is the instantaneous value of back e.m.finduced in the primary coil p1, so theinstantaneous current in primary coil is due to thedifference (E – Ep ) in the instantaneous values ofthe applied and back e.m.f. further if Rp is theresistance o, p1p2 coil, then the instantaneouscurrent Ip in the primary coil is given by I =E – Ep / Rp E – Ep = Ip Rp
When the resistance of the primary is small, Rp Ipcan be neglected so therefore E – Ep = 0 or Ep = EThus back e.m.f = input e.m.fHence equation 3 can be written as Es / Ep = Es / E= output e.m.f / input e.m.f = Ns / Np = KWhere K is constant, called turn or transformationratio.In a step up transformer Es > E so K > 1, hence Ns > NpIn a step down transformer Es < E so K < 1, hence Ns < NpIf Ip=value of primary current at the same instant t
And Is =value of sec. current at this instant,then Input power at the instant t = Ep Ip andOutput power at the same instant = Es IsIf there are no losses of power in the transformer,then Input power = output power or Ep Ip = Es Is Or Es / E p = Ip / Is = KIn a step up transformerAs k > 1, so Ip > Is or Is < IpI.e. current in sec. is weaker when secondaryvoltage is higher. Hence, whatever we gain involtage, we lose in current in the same ratio.Similarly it can be shown, that in a step downtransformer, whatever we lose in voltage, we gainin current in the same ratio.Thus a step up
transformer in reality steps down the current & astep down transformer steps up the current.BASIC IDEA OF STEP DOWN TRANSFORMERBASIC IDEA OF STEP UP TRANSFORMER
EFFICIENCYEfficiency of a transformer is defined as the ratio ofoutput power to the input power i.e.η = output power / input power = Es Is / Ep IpThus in an ideal transformer, where there is nopower losses, η = 1. But in actual practice, thereare many power losses; therefore the efficiency oftransformer is less than one.
ENERGY LOSSESIn practice, the output energy of a transformer is alwaysless than the input energy, because energy losses occurdue to a number of reasons as explained below.1. Loss of Magnetic Flux: The coupling between thecoils is seldom perfect. So, whole of the magnetic fluxproduced by the primary coil is not linked up with thesecondary coil.2. Iron Loss: In actual iron cores in spite of lamination,Eddy currents are produced. The magnitude of eddycurrent may, however be small. And a part of energy islost as the heat produced in the iron core.3. Copper Loss: In practice, the coils of the transformerpossess resistance. So a part of the energy is lost due tothe heat produced in the resistance of the coil.4. Hysteresis Loss: The alternating current in the coiltapes the iron core through complete cycle ofmagnetization. So Energy is lost due to hysteresis.5. Magneto restriction: The alternating current in the
Transformer may be set its parts in to vibrations andsound may be produced. It is called humming. Thus, apart of energy may be lost due to humming. USES OF TRANSFORMERA transformer is used in almost all a.c. operations In voltage regulator for T.V., refrigerator, computer, air conditioner etc. In the induction furnaces. A step down transformer is used for welding purposes. A step down transformer is used for obtaining large current. A step up transformer is used for the production of X-Rays and NEON advertisement. Transformers are used in voltage regulators and stabilized power supplies.
Transformers are used in the transmissions ofa.c. over long distances.Small transformers are used in Radio sets,telephones, loud speakers and electric bellsetc. A Big Transformer
BibliographyThe data used in this project was taken from thefollowing sources: www.google.com www.wikipedia.com www.scribd.com Sears and Zemansky’s University Physics The End