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Branch : Electrical Engineering�Semester : 3rd

Subject : Circuit & Network Theory

Chapter : 01

Topic : Magnetic Circuits

Faculty : Dr. Mrutyunjay Das

Mayurbhanj School Of Engineering, Baripada

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Content

  • Introduction
  • Magnetizing force, Intensity, MMF, Flux and their relations
  • Permeability, Reluctance and Permeance
  • Analogy between Electric and Magnetic circuits
  • B – H Curve
  • Hysteresis loop
  • Series & Parallel magnetic circuit

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Introduction

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Magnetizing force

It is a measure of the influence of a magnet in the surrounding space, also known as magnetic field strength. It is denoted by H and is given by,

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Where N = No. of turns in the coil

I = Current flowing through the coil

L = Length of the coil

 

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Magnetic Intensity &Magneto-motive force (MMF)

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Flux & Flux density

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Permeability

 

 

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Reluctance

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Permeance

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Analogy between Electric and Magnetic circuits

Electrical circuit

Magnetic circuit

Voltage v

Current I

Resistance R

Conductivity 1/ρ

Current density J

Electric field E

Magnetomotive force F = NI

Magnetic flux φ

Reluctance R

Permeability µ

Magnetic flux density B

Magnetic field intensity H

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B – H Curve

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B – H curve for different material is shown below.

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B – H Curve

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Hysteresis loop

The loop formed in one complete cycle of magnetization and demagnetization is known as hysteresis loop.

The area of the hysteresis loop gives the hysteresis loss occurred in a magnetic material due to reversal of magnetic field.

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Hysteresis loop

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  • The flux density remained when current is made zero is known as residual magnetism (a – c & a – f)).
  • This field intensity which forced the magnetic flux to be zero is known as coercive force (a – d & a – g)).
  • The property of the material due to which some magnetic flux density is retained after the field intensity becomes zero is known as retentivity.
  • The area of the hysteresis loop gives the hysteresis loss occurred in the material due to reversal of magnetic field through it.

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Series magnetic circuit

The Series Magnetic Circuit is defined as the magnetic circuit having a number of parts of different dimensions and materials carrying the same magnetic field.

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Series magnetic circuit with its electrical equivalent circuit

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Series magnetic circuit

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Series magnetic circuit

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Series magnetic circuit

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Series magnetic circuit

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Parallel magnetic circuit

  • A magnetic circuit having two or more than two paths for the magnetic flux is called a parallel magnetic circuit.
  • The parallel magnetic circuit contains different dimensional areas and materials having various numbers of paths.

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  • Parallel magnetic circuit with its electrical equivalent circuit

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Parallel magnetic circuit

 

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Parallel magnetic circuit

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Parallel magnetic circuit

 

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Parallel magnetic circuit

 

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Parallel magnetic circuit