Presentation on theme: "ELEMETS OF ELECTRICAL ENGINEERING EDDY CURRENT LOSSES"— Presentation transcript:
1ELEMETS OF ELECTRICAL ENGINEERING EDDY CURRENT LOSSES ACTIVE LEARNING ASSIGNMENTF.Y. COMPUTER ENGINEERINGMADE BY ID. NO. ENROLL. NO.KRUNAL PARMAR 13BECEGVEDANT JOSHI 13BECEMSIDDHARTH PATEL 13BECENKEYUR RANA 13BECEG
2EDDY CURRENTSEddy currents are induced electrical currents that flow in a circular path.They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right.
4EDDY CURRENTSIn order to generate eddy currents for an inspection a “probe” is used. Inside the probe is a length of electrical conductor which is formed into a coil.
5EDDY CURRENTSAlternating current is allowed to flow in the coil at any frequency.
6EDDY CURRENTSA dynamic expanding and collapsing magnetic field forms in and around the coil as the alternating current flows through the coil.
7EDDY CURRENTSWhen an electrically conductive material is placed in the coil’s dynamic magnetic field electromagnetic, induction will occur and eddy currents will be induced in the material.
8EDDY CURRENTSEddy currents flowing in the material will generate their own “secondary” magnetic field which will oppose the coil’s “primary” magnetic field.
9EDDY CURRENTSThis entire electromagnetic induction process to produce eddy currents may occur from several hundred to several million times each second depending upon the frequency.
10EDDY CURRENT LOSSESWhen a conductor, such as armature core of a generator, is either moved to a magnetic field or is present in a magnetic field of alternating current, then according to Faraday’s law of electromagnetic induction, emfs are induced in the coil.Due to these emfs, currents are induced in it. These currents are called eddy currents.
11EDDY CURRENT LOSSESThe figure shows the eddy currents induced in an armature core that is a solid piece of soft iron.
12EDDY CURRENT LOSSESThe power dissipated in the form of heat, as a result of the eddy currents, is considered a loss.Due to the eddy currents ‘Ie’, the conductor becomes hot since a heat energy ‘Ie2R’ is developed, where R is the resistance of the path through which the currents flow.This ‘Ie2R’ loss is called EDDY CURRENT LOSS.
13EDDY CURRENT LOSSESThe eddy current loss is given by We=KBm2f2t2V watt Where, K = constant f = frequency of reversal of magnetism t = thickness of lamination in m Bm = Maximum Flux Density V = Volume of the core
14REDUCING EDDY CURRENT LOSSES It is almost impossible to reduce the iron losses completely; however these can be reduced to a certain extent byUsing Laminated CoresUsing Material Of High Resistivity
15REDUCING EDDY CURRENT LOSSES Using Laminated Cores Thin, laminated strips of metal are used in the construction of power transformers and motors rather than making them out of one solid piece of metal.The thin strips are separated by insulating glue, which confines the eddy currents to the strips.
16REDUCING EDDY CURRENT LOSSES Using Laminated Cores The figure shows a soft iron core of the same size, but made up of several small pieces insulated from each other. This process is called lamination.
17REDUCING EDDY CURRENT LOSSES Using Laminated Cores This arrangement reduces the area of each section and as a result the induced emf induced also decreases,The area through which the eddy currents are now made flow reduces, thus increasing the resistance offered to these currents.
18REDUCING EDDY CURRENT LOSSES Using Laminated Cores The currents in each piece of the laminated core are considerably less than in the solid core because the resistance of the pieces is much higher.The currents in the individual pieces of the laminated core are so small that the sum of the individual currents is much less than the total of eddy currents in the solid iron core.
19REDUCING EDDY CURRENT LOSSES Using Material Having High Resistivity Another method to reduce eddy current losses is to use a magnetic material having high resistivity. Eg : Silicon steel.Thus resistance offered to the flow of these currents will be more and the flow of these currents will be less.