eso 210 lecture 16 2014

ESO 210

Introduction to Electrical Engineering Lecture-16

AC Power Measurement and Magnetic Circuits

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Magnetic Circuits Magnetism plays an integral part in almost every electrical device used today in industry, research or the home.

Generators, motors, transformers, circuit breakers, televisions, computers, tape recorders, and telephones all employ magnetic effects to perform a variety of important tasks.

The compass, used by Chinese sailors as early as the second century A.D., relies on a permanent magnet for indicating direction. The permanent magnet is made of a material, such as steel or iron, that will remain magnetized for long periods of time without the need for an external source of energy.

There is a great deal of similarity between the analyses of electric circuits and magnetic circuits.

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Flux Density

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A curve of the flux density B versus the magnetizing force H of a material is of particular importance. Curves of this type can usually be found in manuals, descriptive pamphlets, and brochures published by manufacturers of magnetic materials. A typical B-H curve for a ferromagnetic material such as steel can be derived using the setup of Fig.

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EXAMPLE: Find the value of I required to establish a magnetic flux of φ=0.75 x 10-4 Wb in the series magnetic circuit of Fig. below

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Solution: An equivalent magnetic circuit and its electric circuit analogy are shown in Fig. The flux density for each section is

g==>Gap

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SERIES-PARALLEL MAGNETIC CIRCUITS

EXAMPLE: Determine the current I required to establish a flux of 1.5x10-4 Wb in the section of the core indicated in Fig. below

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Solution: The equivalent magnetic circuit and the electric circuit analogy appear in Fig. below. We have

From the magnatization curve for sheet steel

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From the magnetization curve:

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EXAMPLE: Calculate the magnetic flux for the magnetic circuit of Fig. below.

Magnetization curve

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EXAMPLE: Find the magnetic flux for the series magnetic circuit of Fig. below for the specified impressed mmf.

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