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L-22(TB)(ET) ((EE)NPTEL)

# L-22(TB)(ET) ((EE)NPTEL) - Module 6 Magnetic Circuits and...

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Module 6 Magnetic Circuits and Core Losses Version 2 EE IIT, Kharagpur

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Lesson 22 Eddy Current & Hysteresis Loss Version 2 EE IIT, Kharagpur
Contents 22 Eddy Current & Hysteresis Losses (Lesson 22) 4 22.1 Lesson goals …………………………………………………………………. 4 22.2 Introduction ………………………………………………………………….. 4 22.2.1 Voltage induced in a stationary coil placed in a time varying field 5 22.2.2 Eddy current ………………………………………………………… 7 22.2.3 Use of thin plates or laminations for core …………………………... 7 22.2.4 Derivation of an expression for eddy current loss in a thin plate …… 8 22.3 Hysteresis Loss ……………………………………………………………… 10 22.3.1 Undirectional time varying exciting current ………………………... 10 22.3.2 Energy stored, energy returned & energy density…………………… 10 22.4 Hysteresis loop with alternating exciting current ……………………………. 12 22.4.1 Hysteresis loss & loop area …………………………………………. 13 22.5 Seperation of core loss ………………………………………………………. 14 22.6 Inductor ……………………………………………………………………… 16 22.7 Force between two opposite faces of the core across an air gap …………….. 18 22.8 Tick the correct answer ……………………………………………………… 19 22.9 Solve the following …………………………………………………………... 20 Version 2 EE IIT, Kharagpur

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Chapter 22 Eddy Current & Hysteresis Losses (Lesson 22) 22.1 Lesson goals In this lesson we shall show that (i) a time varying field will cause eddy currents to be induced in the core causing power loss and (ii) hysteresis effect of the material also causes additional power loss called hysteresis loss . The effect of both the losses will make the core hotter. We must see that these two losses, (together called core loss ) are kept to a minimum in order to increase efficiency of the apparatus such as transformers & rotating machines, where the core of the magnetic circuit is subjected to time varying field. If we want to minimize something we must know the origin and factors on which that something depends. In the following sections we first discuss eddy current phenomenon and then the phenomenon of hysteresis . Finally expressions for (i) inductance, (ii) stored energy density in a magnetic field and (iii) force between parallel faces across the air gap of a magnetic circuit are derived. Key Words : Hysteresis loss; hysteresis loop; eddy current loss; Faraday’s laws; After going through this section students will be able to answer the following questions.
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L-22(TB)(ET) ((EE)NPTEL) - Module 6 Magnetic Circuits and...

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