Project Report Physics XII Transformers

Project Report

Project Report Submitted On Transformer

Class – XII

Submitted To: Miss. Sunita

Submitted By: Pankaj Gill

Dept. of Physics

Class – XII

Certificate This is to certify that Pankaj Gill, Gill student of Class XII, Mahendra Model Sr. Sec. School has completed the project titled Transformer during the academic year 2009-2010 towards partial fulfillment of credit for the Physics practical evaluation of CBSE 2010, and submitted satisfactory report, as compiled in the following pages, under my supervision.

Miss. Sunita Department of Physics Mahendra Model Sr. Sr. School

Acknowledgements "There are times when silence speaks so much more loudly than words of praise to only as good as belittle a person, whose words do not express, but only put a veneer over true feelings, which are of gratitude at this point of time."

I would like to express my sincere gratitude to my physics mentor Miss. Sunita , for her 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 Mahendra Model Sr. Sec. School for their support during the making of this project.

(Pankaj Gill) Gill)

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.

PRINCIPLE

It is based on the principle of mutual induction that is if a varying current is set-up in a circuit induced e.m.f. is produced in the neighboring circuit. The varying current in a circuit produce varying magnetic flux which induces e.m.f. in the neighboring circuit.

STEP-DOWN TRANSFORMER

In our project step-down transformer is used: This transformer converts high voltage at alternating current into low voltage alternating current. In step-down transformer the number of turns in primary coil remains large as compare to secondary coil.

CONSTRUCTION

The transformer consists of two coils. They are insulated with each other by insulated material and wound on a common core. 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 primary. And the output circuit is called secondary.

THEORY Suppose, the number of turns in the primary coil is NP and that in the secondary coil is NS. The resistance of the coil is assumed to be zero. Let dq/dt be the rate of change of flux in each turn of the primary coil. If Ep be the e.m.f. in the primary circuit then. EP = –NP

(1)

We suppose that there is no loss of flux between the primary and secondary coils. Then, the induced e.m.f. in the secondary coil will be: ES = –NS

(2)

From equations (i) and (ii), we find: Ns/Np = K is called transformer ratio or turn ratio. For step up transformer K > 1 For step down transformer K < 1 That is for step-up transformer NS > NP, therefore ES>EP. For the step down transformer NS < NP therefore ES < EP.

Efficiency: The efficiency of the transformer is given by:

If Ip and Is be the currents in the primary and secondary circuits.

For ideal transformer

= 1 = 100%.

Therefore ESIS = EPIP Or

Therefore, for step up, transformer current in the secondary is less than in the primary (IS < IP). And in a step down transformer we have IS > IP.

Energy

Losses

in

Transformer

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, 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 inspite of lamination,

Eddy currents are produced. The magnitude of eddy current may, however be small. And a part of 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 complete cycle of magnetization. So Energy is lost due to hysteresis. 5.

Magneto restriction: The alternating current in the

Transformer may be set its parts in to vibrations and sound may be produced. It is called humming. Thus, a part of energy may be lost due to humming.