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I would like to express my sincere gratitude to my physics mentor 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 staff of the Department of Physics at LMS International School for their support during the making of this project.
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. It is a static electrical device that transfers energy by inductive coupling between its winding circuits. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used in power plant substations or to interconnect portions of the power grid.
All operate on the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in many electronic devices. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical. A transformer is the most widely used device in both low and high current circuit.
In a transformer, the electrical energy transfer from one circuit to another circuit takes place without the use of moving parts. A transformer which increases the voltages is called a step-up transformer. A. The transformer which decreases the A.C. voltages is called a step-down transformer. The transformer is, therefore, an essential piece of apparatus both for high and low current circuits. Close-up of single-phase pole mount transformer
It is based on the principle of mutual induction that is if a varying current is a set-up in a circuit then induced e.m.f. is produced in the neighboring circuit. The varying current in a circuit produces varying magnetic flux which induces e.m.f. in the neighboring circuit.
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 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. For operation at low frequency, we may have a soft iron. The soft iron core is insulating by joining thin iron strips coated with varnish to insulate them to reduce energy losses by eddy currents. The input circuit is called the primary. And the output circuit is called secondary.
THEORY AND WORKING
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, the whole of the magnetic flux linked with the primary is also linked with the secondary, and then the induced e.m.f. induced in each turn of the secondary is equal to that induced in each turn of the 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 turn of 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 the 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
I =E – Ep / Rp 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.
In a step up transformer
Es > E so K > 1, hence Ns > Np
In 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 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 / E p = Ip / Is = KIn a step up transformer As k > 1, so Ip > Is or Is < IpI.e. current in Sec. is weaker when the secondary voltage is higher. Hence, whatever we gain in voltage, we lose in current in the same ratio. Similarly,
it can be shown, that in a step down transformer, whatever we lose in voltage, we gain in current in the same ratio. Thus a step up transformer, in reality, steps down the current & a step down transformer steps up the current.
The 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.
In practice, the output energy of a transformer is always less than the input energy, because energy losses occur due to a number of reasons as explained below.1. Loss of Magnetic Flux: The coupling between the coils is seldom perfect. So, the whole of the magnetic flux produced by the primary coil is not linked up with the secondary coil.2. Iron Loss: In actual iron cores in spite of lamination, Eddy currents are produced.
The magnitude of eddy current may, however, be small. And a part of the energy is lost as the heat produced in the iron core.3. Copper Loss: In practice, the coils of the transformer possess resistance. So a part of the energy is lost due to the heat produced in the resistance of the coil.4. Hysteresis Loss: The alternating current in the coil tapes the iron core through a complete cycle of magnetization. So Energy is lost due to hysteresis.5. Magneto restriction: The alternating current in the
- 17. The transformer may be set its parts into vibrations and sound may be produced. It is called humming. Thus, apart of energy may be lost due to humming. USES OF TRANSFORMER A 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 a 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 of a.c. over long distances. Small transformers are used in Radio sets, telephones, loudspeakers and electric bell, etc. End of School Project on Transformer.