SESSION 2012-13
PROJECT PREPARED BY:RAUSHAN KUMAR XII M
Submitted to JESUS $ MARY MARY ACADEMY, DARBHANGA
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CERTIFICATE This This is hereb reby to cert certif ify y tha that, the the orig riginal inal and and genuine Investigation work has been carried out to investig tigate about the subjec ject mat matter and the the related data collection and investigation has been comple completed ted solely solely,, sincer sincerely ely and and satisf satisfact actori orily ly by RAUSHAN KUMAR of CLASS XII M , JESUS $ regard rdin ing g his his proj projec ectt titl titled ed MARY MARY ACADE ACADEMY MY,, rega “A.C TRANSFORMER”.
Date _ _/_ _/_ _ _ _ Place:- DARBHANGA
Examiner’s signature
Teacher’s Signature
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Aim
To inv investig tigate the rela elation tion bet between een the ratio of:1. Inpu Inputt and ou output put volta oltage ge 2. number of turns in secondary coil of self designed transformer.
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ACKNOWLEDGEMENT
It would be my utmost pleasure to express my sincere thanks to My Physics Teacher …………………………. in providing a helping hand in this this projec project. t. Their Their valua valuable ble guid guidanc ance, e, suppo support rt and supervision all through this project titled “ A.C Transformer ” are are resp respon onsi sibl ble e for for atta attain inin ing g its its present form. ,
RAUSHAN KUMAR XII M
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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.
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Construction: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 p 1 p p2, the primary coil and a load resistance R is connected to s 1 s2, the secondary coil through an open switch S. thus there can be no current current through the 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.
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INTRODUCTION A transformer is an electrical device which is used for changing the A.C. voltages. A transformer is most widely used device in both low and high current circuit. As such tran transf sfor orme mers rs are are buil builtt in an amaz amazin ing g stre streng ngth th of size sizes. s. In electronic, measurement and control circuits, transformer size may be so small that it weight only a few tens of grams where as in high voltage power circuits, it may weight hundred of tones. In a transformer, the electrical energy transfer from one circuit to another circuit takes place without the use of moving parts. A tran transf sfor orme merr whic which h incr increa ease sess the the volt voltag ages es is called a step-up transformer. A transformer which decreases the A.C. voltages is called a step-down transformer. Transf Transfor orme merr is, theref therefor ore, e, an essent essential ial piece piece of apparatus both for high and low current circuits.
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THEORY AND WORKING WORKING
When an altering e.m.f. is supplied to the primary coil p 1 p p2, an alternating current starts falling in it. The altering current in the the prim primar ary y prod produc uces es a chan changi ging ng magn magnet etic ic flux flux,, whic which h indu induce cess alte alteri ring ng volt voltag agee in the the prim primar ary y as well well as in the 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 primary. Thus if E p and Es be the instantaneous values of the e.m.f.’s induced in the primary and the secondary and N p 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 E p = -N p dфь/dt
-----------------(1)
And 8
Es = -Ns dфь/dt
----------------- (2)
Sinc Sincee the the abov abovee rela relati tion onss are are true true at ever every y inst instan ant, t, so by dividing 2 by 1, we get Es / E p = - Ns / N p
----------------(3)
As E p is the instantaneous value of back e.m.f induced in the primary coil p 1, so the instantaneous current in primary coil is due to the difference (E – E p ) in the instantaneous values of the applied and back e.m.f. further if R p is the resistance o, p1 p p2 coil, then the the instantaneous current Ip in the primary primary coil is given by
I p
= E – E p / R p
E – E p = I p R p When the resistance of the primary is small, R p p I p can be neglected so therefore E – E p = 0 or E p = E 9
Thus back e.m.f = input input e.m.f e.m.f Hence equation 3 can be written as Es / E p = Es / E = output e.m.f / input e.m.f = Ns / N p = K Where K is constant, called turn or transformation ratio. In a step up transformer
Es > E so K > 1, hence Ns > N p In a step down transformer
Es < E so K < 1, hence Ns < N p If
I p =
And
Is
=
value of primary current at the same instant t value of sec. current at this instant, then
Input power at the instant t
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=
E p I p and
Output power at the same instant
=
Es Is
If there are no losses of power in the transformer, then Input power = output power E p I p = Es / E p
=
Or
Es Is I p / Is
Or =
K
In a step up transformer
As k > 1, 1, so I p > Is or Is < Ip i.e. current in sec. is weaker when 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.
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How to Wire a Step Down Transformer •
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Observe and identify the schematic and rating of the step down transformer to be installed. Remove the terminal connection box cover placed at the lower side of the transformer. transformer. Only the high amperage types will have this enclosure, while lower powered transformers will have an exposed screw terminal. Know termination identification follows for all step down transformers: transformers: H1, H2, H3 and H4 signify the high voltage side or power feed end of the transformer. This holds true regardless of the size of the transformer. Interconnection of the transformer will vary depending on the manufacturer and voltage used for feeding the transformer. Terminate the feed power wires first by cutting the wires to length. If you are using large wire lugs be sure to take into consideration the length of the lug and the amount of wire that can be inserted into the female crimp area. Strip back the outer insulating of the wires with the pocketknife pocketknife or wire strippers. strippers. Insert the eye ring ring or wire lug over the bare copper wire and crimp the connection device, using the appropriate-size crimper, permanently to the wire. Terminate the high side, high voltage of the step down transformer. transformer. If the high side terminals are bolts, be sure to follow any torque requirements that are listed by the manufacturer. Terminate the low side, low voltage of the transformer. Note these terminals terminals will be identified identified by X1, X2, X3 12
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and X4. Again follow the manufacturer’s individual schematics for that particular type of transformer. Note that on small control transformers there will only be an X1 and X2. X1 is the power or “hot” side and X2 is generally the grounding and neutral portion of the low voltage. Terminate the small control transformer for X1 and X2. X1 will go directly to the control circuit after passing through a small fuse that is rated for the circuit. X2 will be terminated terminated not only to the neutral neutral side of the control circuit, but the grounding safety as well. In other words, the X2 side of the small control transformer must be tied to the grounding system of the electrical circuit. Replace all covers on the transformer and any enclosures that protect you from electricity. Apply the high voltage to the transformer by switching on the feeder power circuit. Turn on the low side safety circuit control. Use a volt meter to test for proper voltage voltage on the step down side of the transformer. It should be the same that is listed on the specs tag provided by the manufacturer. manufacturer.
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How to Check a Step Down Transformer •
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Remove all wires from the transformer terminals using the screwdriver. Identify the wires if they are not already identified. Use a clear tape and pen. Write the terminal that the wires are attached to and place the identified tape on the wire’s end. Turn the volt ohmmeter to the “Ohms” position and place the red lead lead into the connector connector identified identified as “Ohms.” Touch the black lead to the metal frame of the transformer. Touch the red lead to the transformer’s terminals terminals in the following order: H1, H2, X1 and then X2. The meter should read infinite ohms or wide open. Infinite ohms on a digital meter will be identified as a blank screen or a wide open will have the word “Open” displayed. If the meter registers any form of resistance, there is an internal problem with the windings. The The copper coils may may be shorted to the metal frame of the transformer. The transformer transformer will have to be replaced. Check the continuity of each separate coil using the ohmmeter. Touch the black lead to H1 and the red lead to H2. The meter should give a resistance reading. Generally, it should read in the range of 3 to 100 ohms, depending on the style and type of transformer. Perform the same test to the X1 and X2 terminals. You should receive the same results. If the meter reads infinite ohms or a wide open when checking between the terminals of
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the same coil, the wires are broken. Replace the transformer. Use the ohmmeter to conduct the transformers isolation circuit. Touch the red lead to H1 and the black lead to X1. The meter should read infinite ohms or a wide-open circuit. Perform the same test, but to H2 and X2 respectively. If any resistance at all is read on the meter other than a wide-open circuit, the isolation of the transformer has been compromised and must be replaced.
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Efficiency:Efficiency of a transformer is defined as the ratio of output power to the input input power. i.e. η =
output power / input power =
Es Is /
E p I p Thus in an ideal transformer, where there is no power losses, η = 1. But But in actual actual pract practice, ice, there there are are many many power power losses, losses, therefore the efficiency of transformer transformer is less than one.
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ENERGY LOSSES: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 S 1S2 is less than the rate of change of magnetic flux linked with each turn of P 1P2.
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Hystereti eticc loss loss is the 4. Hyster the loss loss of energy ergy due to repeate eated d
magn magneti etizat zation ion and dema demagne gnetiz tizati ation on of the iron iron core core when when A.C. is fed to it. 5. Magneto striation i.e. humming noise of a transformer.
COCLUSION 1. The The outpu outputt volta voltage ge of the the tran transf sfor orme merr acros acrosss the secondary coil depends upon the ratio(Ns/Np) with respect to input voltage. 2.
The The output output voltag voltagee of the transf transform ormer er across across the secondary coil depends upon the ratio(Ns/Np) with respect to input current.
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There is a loss power between input and output coil of a transformer.
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USES A transformer is used in almost all a.c. operations operations •
In voltag ltagee regu egulato latorr for T.V T.V., refri efrig gerat erato or, computer, air conditioner etc. In the induction furnaces.
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A step step down down tran transf sfor orm mer is used used for for weld weldin ing g purposes. A step step down down tran transf sfor orme merr is used used for for obta obtain inin ing g large current. A step up transformer is used for the production of X-Rays and NEON advertisement. advertisement. Transformers are used in voltage regulators and stabilized power supplies. Transformers are used in the transmissions of a.c. over long distances. 19
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Small transformers are used in Radio sets, telephones, loud speakers and electric bells etc.
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BIBLIOPGRAPHY
1.
Comprehensive lab manual
2. Prade Pradeep’ ep’ss physics physics 3.
www.yahoo.com
4.
www.google.com
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