30. Nov 2014

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  1. TRANSFORMER Group no. – 13 First year bridge course By :- RISHI MERVANA 14BEEEG025 NISARG AMIN 14BEEEG012 URVISH PATEL 14BEEEM032 DARSHAN MAHAVAR 14BEEEG029 Guide Teacher :- S.M.Pujara
  2. Introduction: The alternating current has several advantages over direct current is that, Alternating Current can be easily transferable from low to high voltage Alternating voltage can be raised or lowered as per requirement by a static device called TRANSFORMER
  3. What is a transformer?  A static piece of apparatus by means of which an electrical power is transferred from one alternating current circuit to another electrical circuit  There is no electrical contact between them.  The desire change in voltage or current, without any change in frequency.  Symbolically the transformer Denoted as,
  5. Structure of Transformer:  The transformer consists of 2 inductive coils, they are electrically separated but linked through a common magnetic circuit. They have high mutual induction  One of them is connected to a source of alternating voltage. This coil in which electrical energy is fed with the help of source called primary winding(P).  The other winding is connected to a load. The electrical energy is transformed to this winding drawn out to the load. This winding is called secondary winding(S).
  6.  The primary & secondary coil wound on a ferromagnetic metal core. The function of the core is to transfer the changing magnetic flux from the primary coil to secondary coil.  The no. of turns plays an important role in the function of transformer.
  7. Working Principle:  The transformer works in the principal of mutual induction.  “ The principle of mutual induction states that when 2 coils are inductively coupled and if the current in coil change uniformly then the e.m.f induced in the other coil. This e.m.f can drive a current when a closed path is provided to it.”  When an Alternating current flows in Primary coil, a changing magnetic flux is generated around the primary coil.
  8.  The changing magnetic flux is transferred to the secondary coil through the iron core.  The changing magnetic flux is cut by the secondary coil, hence induces e.m.f. in the secondary coil.  Now if load is connected to a secondary winding, this e.m.f. drives a current through it.  The magnitude of the output voltage can be controlled by the ratio of the no. of primary coil & secondary coil.  “The frequency of mutually induced e.m.f as same that of the alternating source which supplying energy to the primary winding”
  10. Construction:  There are 2 basics of transformer contraction. 1. Magnetic Core 2. Windings or coils  MAGNETIC CORE:  The core of transformer either square or rectangular type in size  Core is made of laminations. Because of laminated core type constructions, eddy current losses get minimize.  Generally high grade silicon steel laminations (0.3 to 0.5 mm) are used.  These lamination are insulated from each other by using insulation like varnish or thick paper.
  11. Windings:  Conducting material is used in the windings of the transformer.  The coils used are wound on the limbs and insulated from each other.  The 2 different windings are wounds on 2 different limbs i.e. primary on 1 limbs while secondary on other limb in the basic transformer.  The leakage flux increase which affects the performance and efficiency of transformer.  To reduce the leakage flux it is necessary that the windings should be very close to each other to have high mutual induction.
  12. Core type Construction:  In the core type 1 magnetic circuit & cylindrical coils are used.  These coils are mechanically strong.  Normally L & T shaped laminations are used.  Commonly primary winding wound on 1 limb while secondary on the other but performance will be reduce.  To get high performance it is necessary that the 2 windings should be very close to each other.
  13. Shell type construction:  In the shell type 2 magnetic circuit are used.  The windings is wound on central limbs.  For the shell type each high voltage winding lie between 2 low voltage portion sandwiching the high voltage winding.  Sub-division of windings reduces the leakage flux.  All the portions are insulated by paper.  Greater the no. of sub-divisions lesser the reactance.  This type of construction is used for high voltages.
  14. Losses In Transformer:  In transformer, there exists 2 types of losses. 1. Core losses 2. Copper losses  Core losses: It has also 2 types of losses. 1. Hysteresis loss: During magnetization and demagnetization, due to hysteresis effect some energy losses in the core called hysteresis. 2. Eddy current loss: The leakage magnetic flux generates the e.m.f. in the core produces current is called eddy current loss.
  15. Copper losses  The copper losses is due to power wasted in the form of I2r due to resistance of primary and secondary. The magnitude of copper losses depend upon the current flowing through these coils. “The iron losses depend on the supply voltage while the copper losses depend upon the current. The losses are not dependent on the phase angle between the voltage and current.”
  16. Types of transformer: Step up transformer  No. of secondary windings are greater than the no. of primary windings(Ns> Np).  It converts low alternate voltage to high alternate voltage.  This type of transformer is called step up transformer. Step down transformer  No. of primary windings are greater than the no. of secondary windings (Np> Ns).  It converts high alternate voltage to low alternate voltage.  This type of transformer is called step down transformer.
  17. Ideal V/S Practice Transformer: A transformer is said to be ideal if it satisfies the following properties, but no transformer is ideal in practice.  It has no losses  Windings resistance are zero  There is no flux leakage  Small current is required to produce the magnetic field While the practical transformer has winding resistance, some leakage flux and has little bit losses.
  18. Can a transformer step up or step down the DC current or voltage?  The DC supply cannot be used for transformer.  Because the transformer works on the principle of mutual induction, for which the current in the coil changes uniformly. If DC supply is applied the current does not change uniformly due to constant supply and transformer will not work. “The DC supply may cause the transformer to damage permanently”
  19. Applications & Uses:  The transformer is used in Television and photocopy machines.  The transformer(ballast transformer) are also installed in fluorescent tube lights.  The transmission & distribution of alternating power is possible by transformer.  Simple camera flash uses fly back transformer.  Signals and audio transformer are used couple in amplifier. “Today transformer has become an essential part of electronics engineering”
  20. THANKS ALL!!!