ELEMETS OF ELECTRICAL ENGINEERING EDDY CURRENT LOSSES ACTIVE LEARNING ASSIGNMENT F.Y. COMPUTER ENGINEERING MADE BY ID. NO. ENROLL. NO. KRUNAL PARMAR 13BECEG017 130410107025 VEDANT JOSHI 13BECEM036 130410107034 SIDDHARTH PATEL 13BECEN055 130410107077 KEYUR RANA 13BECEG063 130410107088

EDDY CURRENTS Eddy 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.

EDDY CURRENTS Test Probe Eddy Currents

EDDY CURRENTS In 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.

EDDY CURRENTS Alternating current is allowed to flow in the coil at any frequency.

EDDY CURRENTS A dynamic expanding and collapsing magnetic field forms in and around the coil as the alternating current flows through the coil.

EDDY CURRENTS When 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.

EDDY CURRENTS Eddy currents flowing in the material will generate their own “secondary” magnetic field which will oppose the coil’s “primary” magnetic field.

EDDY CURRENTS This entire electromagnetic induction process to produce eddy currents may occur from several hundred to several million times each second depending upon the frequency.

EDDY CURRENT LOSSES When 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.

EDDY CURRENT LOSSES The figure shows the eddy currents induced in an armature core that is a solid piece of soft iron.

EDDY CURRENT LOSSES The 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.

EDDY CURRENT LOSSES The 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

REDUCING EDDY CURRENT LOSSES It is almost impossible to reduce the iron losses completely; however these can be reduced to a certain extent by Using Laminated Cores Using Material Of High Resistivity

REDUCING 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.

REDUCING 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.

REDUCING 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.

REDUCING 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.

REDUCING 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.

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