Electrical Transformer

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Electrical Transformer

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Transformer :

Transformer What is Transformer? Structure & Working Principle? Construction of Transformer? Losses in Transformer? Types of Transformer? Ideal VS Practical Transformer? Uses & Application of Transformer? Muddasir Arain (11ES112) Ayaz Mari (11ES97 ) Shehbaz Agha (11ES136) Zeeshan Anwar (11ES138) Juma Khan (11ES143 ) Saddam Dogar (11ES111) Burhan Arain GL (11ES104) (The Heart of Alternating Current System).

Introduction::

Introduction: The Alternating current has several advantages over direct current is that, The alternating current can easily transferable from low to high voltage or high to low voltage. The alternating voltage can be raised or lowered as per requirement at different stages in an electrical network, such as generation, transformation, distribution and utilization. This is possible with static device called transformer.

What is Transformer?:

What is Transformer ? A transformer is a static piece of apparatus by means of which an electrical power is transferred from one alternating current circuit to another electrical circuit. T here is no electrical contact between them. T he desire change in voltage or current, with out any change in frequency. Symbolically the transformer denoted as, Note: It works on the principles of mutual induction.

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Structure of Transformer::

Structure of Transformer: The transformer consists two inductive coils, these are electrically separated but linked through a common magnetic circuit. These two coils have a high mutual induction. One of the two coils 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), as shown in figure . 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 ), also as shown in figure

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The primary and 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 the secondary coil. The primary has N 1 numbers of turns and the secondary has N 2 numbers of turns. The of turns plays major important role in the function of transformer.

Working Principle::

The transformer works in the principle of mutual induction. When an alternating current flows in the primary coil, a changing magnetic flux is generated around the primary coil . “The principle of mutual induction states that when the two 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.” Working Principle:

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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 an 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 number of primary coil and secondary coil. “The frequency of mutually induced e.m.f as same that of the alternating source which supplying energy to the primary winding b

Construction of Transformer::

Construction of Transformer: There are two basics of transformer contraction. Magnetic Core. Windings or Coils. Magnetic Core: The core of transformer either square or rectangular type in size. It is further divided into two parts Vertical and Horizontal. The vertical portion on which coils are wound is called limb while Horizontal portion is called Yoke. These parts are shown in fig.

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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.

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Windings: Conducting material is used in the windings of the transformer. The coils used are wound on the limbs and insulated from each other. T he two different windings are wounds on two different limbs i.e. primary on one limbs while secondary on other limb in the basic transformer. The leakage flux increases which affects the performance and efficiency of transformer. To reduces the leakage flux it is necessary that the windings should be very close to each other to have high mutual induction .

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Core type Construction : In the core type one magnetic circuit and cylindrical coils are used. These coils are mechanically strong. Normally L and T shaped laminations are used. Commonly primary winding wound on one limb while secondary on the other but performance will be reduce. To get high performance it is necessary that the two windings should be very close to each other. The low voltage winding is placed near the core from ease insulating it from the core. The high voltage is placed after it.

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Shell Type Construction: In the shell type two magnetic circuit are used. The windings is wound on central limbs. For the shell type each high voltage winding lie between two 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 number of sub-division lesser the reactance. This type of construction is used for high voltages.

Losses In Transformer::

Losses In Transformer: In transformer, there are exists two type losses. Core Losses. Copper Losses. Copper Losses : I t has also two types of losses. Hysteresis Loss. During magnetization and demagnetization, due to hysteresis effect some energy losses in the core called Hysteresis Loss. Eddy Current Loss: The Leakage magnetic flux generates the e.m.f in the core produces current is called of E ddy Current Loss.

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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 on the current. The losses are not dependent on the phase angle between current and voltage. Hence the rating o f the transformer is expressed as a product of voltage and current called VA rating of transformer. It is not expressed in watts or kilowatts. Most of the times, rating is expressed in KVA.

Types of Transformer::

Types of Transformer: Generally the transformer classify accordingly transformation ratios are: 1. Step-up Transformer: 2. Step-down Transformer 1. Step-up Transformer: A transformer in which Ns> Np is called a step up transformer. A step up transformer is a transformer which converts low alternate voltage to high alternate voltage . 2. Step-down Transformer: A transformer in which Np >Ns is called a step down transformer. A step down transformer is a transformer which converts high alternatic voltage to low alternatic voltage.

Ideal V/S Practical Transformer::

Ideal V/S Practical 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 windings resistance, some leakage flux and has little bit losses

Can a transformer step up or step down the DC current or voltage?:

Can a transformer step up or step down the DC current or voltage? The DC supply can not be used for transformer. Because the transformer works on the principle of mutual induction, for which the current in coil changes uniformly. If DC supply is apply the current does not change uniformly due to constant supply and transformer will not work. “The DC supply may cause the transformer to the damage permanently .”

Application & Uses;:

Application & Uses; The transformer used in television and photocopy machines. The transformer (ballast transformer) are also installed in fluorescent tube light . The transmission and distribution of alternating power is possible by transformer. Simple camera flash uses fly back transformer. Signals and audio transformer are used couple in amplifier. “Todays transformer is become an essential part of electronics engineering.”

References: :

References: Electrical Engineering by UA Bakshi. Introductory Circuit Analysis by Robert T. Boylasted . Principle of Electrical Machine VK Mehta. Electrical Machines by RK Rajput. Electrical Machines by Muhammad Haris Latif. www.allaboutcircuit.com www.iiee.com

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