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Step down transformer

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LORD MAHAVIRA
ACADMEY
10+2 English Medium
(Affiliated to CBSE, New Delhi)
Chilkana Road, Saharanpur-247001
Report on Proje...
Acknowledgements
I would like to express my sincere gratitude to my physics mentor
MR. PANKAJ SIR for his vital support, g...
CERTIFICATE
This is to certify that TEJASH BANSAL, student of Class XII,
LORD MAHAVIRA ACADEMY, SAHARANPUR has
completed t...
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Step down transformer

  1. 1. LORD MAHAVIRA ACADMEY 10+2 English Medium (Affiliated to CBSE, New Delhi) Chilkana Road, Saharanpur-247001 Report on Project STEP DOWN TRANSFORMER SESSION: 2017-18
  2. 2. Acknowledgements I would like to express my sincere gratitude to my physics mentor MR. PANKAJ SIR for his vital support, guidance and encouragement, without which this project would not have come forth. I would also like to express my gratitude to the OTHER staff of the Department of Physics for their support during the making of this project. (TEJASH BANSAL)
  3. 3. CERTIFICATE This is to certify that TEJASH BANSAL, student of Class XII, LORD MAHAVIRA ACADEMY, SAHARANPUR has completed the project titled Transformer during the academic year 2017-2018 towards partial fulfillment of credit for the Physics practical evaluation of CBSE 2017, and submitted satisfactory report, as compiled in the following pages, under my supervision. Principal Physics lecturer Mrs Priya Jain PANKAJ SIR
  4. 4. CONTENTS 1. INTRODUCTION 2. OBJECTIVES 3. PRINCIPLE 4. CONSTRUCTION 5. THEORY 6. EFFICIENCY 7. CIRCUIT DAIGRAM 8. ENERGY LOSSES IN TRANSFORMER 9. USES 10. APPLICATIONS 11. PRECAUTIONS 12. BIBLIOGRAPHY
  5. 5. INTRODUCTION The transformer is a device used for converting a low alternating voltage to a high alternating voltage or a high alternating voltage into a low alternating voltage. A transformer which increases the a.c. voltage is called a “step up transformer”
  6. 6. A STEP DOWN TRANSFORMER A step-down transformer is one whose secondary voltage is less than its primary voltage. It is designed to reduce the voltage from the primary winding to the secondary winding. This kind of transformer “step down” the voltage applied to it As a step-down unit, the transformer convert high-voltage, low- current power into low-voltage, high-current power. OBJECTIVE Prepare a project on “STEP DOWN TRANSFORMER” PRINCIPLE A Transformer based on the Principle of mutual induction according to this principle, the amount of magnetic flux linked with a coil changing, an e.m.f is induced in the neighbouring coil. CONSTRUCTION
  7. 7. A transformer consists of a rectangular shaft iron core made of laminated sheets, well insulated from one another. Two coils p1 & p2 and s1 & s2 are wound on the same core, but are well insulated with each other. Note that the both the coils are insulated from the core, the source of alternating e.m.f is connected to p1p2, the primary coil and a load resistance R is connected to s1 s2, the secondary coil through an open switch S. thus there can be no current through the sec. coil so long as the switch is open. For an ideal transformer, we assume that the resistance of the primary & secondary winding is negligible. Further, the energy loses due to magnetic the iron core is also negligible. THEORY When an altering e.m.f. is supplied to the primary coil p1p2, an alternating current starts falling in it. The altering current in the primary produces a changing magnetic flux, which induces altering voltage in the primary as well as in the secondary. In a good- transformer, whole of the magnetic flux linked with primary is also linked with the secondary, then the induced e.m.f. induced in each turn of the secondary is equal to that induced in each turn of the
  8. 8. primary. Thus if Ep and Es be the instantaneous values of the e.m.f.’s induced in the primary and the secondary and Np and Ns are the no. of turns of the primary secondary coils of the transformer and Dфь / dt = rate of change of flux in each turnoff the coil at this instant, we have Ep = -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.f induced in the primary coil p1, so the instantaneous current in primary coil is due to the difference (E – Ep ) in the instantaneous values of the applied and back e.m.f. further if Rp is the resistance o, p1p2 coil, then the instantaneous current Ip in the primary coil is given by Ip = E – Ep / Rp
  9. 9. E – Ep = Ip Rp When the resistance of the primary is small, Rp Ip can be neglected so therefore E – Ep = 0 or Ep = E Thus back e.m.f = input e.m.f Hence equation 3 can be written as Es / Ep = Es / E = output e.m.f / input e.m.f = Ns / Np = K Where K is constant, called turn or transformation ratio.
  10. 10. In a step down transformer Es < E so K < 1, hence Ns < Np If 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 and Output power at the same instant = Es Is If there are no losses of power in the transformer, then Input power = output power Or Ep Ip = Es Is Or Es / Ep = Ip / Is = k
  11. 11. Efficiency:- Efficiency of a transformer is defined as the ratio of output power to the input power. i.e. η = output power / input power = Es Is / Ep Ip Thus in an ideal transformer, where there is no power losses, η = 1. But in actual practice, there are many power losses, therefore the efficiency of transformer is less than one. CIRCUIT DIAGRAM ENERGY LOSSES:-
  12. 12. Following are the major sources of energy loss in a transformer: 1. Copper loss is the energy loss in the form of heat in the copper coils of a transformer. This is due to joule heating of conducting wires. 2. Iron loss is the energy loss in the form of heat in the iron core of the transformer. This is due to formation of eddy currents in iron core. It is minimized by taking laminated cores. 3. Leakage of magnetic flux occurs inspite of best insulations. Therefore, rate of change of magnetic flux linked with each turn of S1S2 is less than the rate of change of magnetic flux linked with each turn of P1P2. 4. Hysteretic loss is the loss of energy due to repeated magnetization and demagnetization of the iron core when A.C. is fed to it. 5. Magneto striation i.e. humming noise of a transformer. USES OF TRANSFORMER
  13. 13. A transformer is used in almost all a.c. operations 1· In voltage regulator for T.V., refrigerator, computer, air conditioner etc. 2. In the induction furnaces. 3. A step down transformer is used for welding purposes. 4. A step down transformer is used for obtaining large current. 5. In transmission of a.c. over long distance. APPLICATIONS
  14. 14. A major application of transformer is to increases voltage before transmitting electrical energy over long distance through wires. Wires have resistance and so dissipate electrical energy at a rate proportional to the square of the current through the wire. By transforming electrical power to a high-voltage (and there for low- current) form for transmission and back again afterward, transformers enable economical transmission of power over long distance. Consequently, transformers have shaped the electrical supply industry, permitting generation to be located remotely from points of demand. All but a tiny fraction of the world’s electrical power has passed through a series of transforms by the time it reaches the consumer. Transformer are also used extensively in electronic products to step down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also used electrically isolates the end user from contact with the supply voltage. Transformer range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge unit weighing hundreds of tons used in power stations, or to interconnect portions of power grids. All operate on the same basic principles, although the range of designs is wide. While new technologies have eliminated
  15. 15. the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household (“mains”) voltage. Transformer are essential for high-voltage electrical power transmission, which makes long-distance transmission economically practical. Single and audio transformer are used to couple stages of amplifier and to match devices such as microphones and record players to the input of the amplifiers. Audio transformer allowed telephone circuit to carry on a two-way conservation over a single pair of wires. A balun transformer converts a single that is referenced to ground to a signal that has balanced voltage to ground, such as between external cables and internal circuits. PRECAUTIONS
  16. 16. 1. The loss of power in the transmission lines is I2 R, where I is strength of current and R is the resistance of wires. To reduce the power loss, a.c. is transmitted over long distance at extremely high voltages. This reduces I in the same ratio. Therefore, I2 R becomes negligibly low. 2. Permeability of magnetic material of transformer core must be high. 3. Oiling in transformer provides insulation as well as cooling. 4. The transformer core must be laminated to minimize loss of energy due to eddy currents. 5. Safety from high voltage is maintained.
  17. 17. BIBLIOGRAPHY 1. Physics textbook for class XII ,1st Edition NCERT (2007). 2. Concepts of Physics, H.C.VERMA, 1ST Edition, Bharti bhawan(1993). 3. Fundamentals of Physics , David Halliday, Robert resnick and Jearl walker, 7th Edition, Wiley-India(2004) 4. Practical physics for class XII, J.S.Jaiswaland Dr.Rajendra singh ,3rd Edition ,Laxmi Publications(2009).

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