# Magnetic Circuit

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Magnetomotive Force (MMF)

Reluctance

Magnetic CircuitS UBHASH PATELElectronics & Communication

Year 2010

Magnetomotive Force (MMF)

Reluctance

Outline

1

Magnetomotive Force (MMF)

Magnetomotive Force (MMF)

Reluctance

Outline

1

Magnetomotive Force (MMF)

2

Reluctance

Magnetomotive Force (MMF)

Reluctance

Magnetomotive Force (MMF)The current owing in the electrical circuit due to the existence of electromotive force(emf) across the circuit

Magnetomotive Force (MMF)

Reluctance

Magnetomotive Force (MMF)The current owing in the electrical circuit due to the existence of electromotive force(emf) across the circuit To drive magnetic ux through magnetic circuit, a magneto motive force (mmf) is necessary.

Magnetomotive Force (MMF)

Reluctance

Magnetomotive Force (MMF)The current owing in the electrical circuit due to the existence of electromotive force(emf) across the circuit To drive magnetic ux through magnetic circuit, a magneto motive force (mmf) is necessary. Magnetomotive force can be produced when current ows in a coil of one or more turns.

Magnetomotive Force (MMF)

Reluctance

Magnetomotive Force (MMF)The current owing in the electrical circuit due to the existence of electromotive force(emf) across the circuit To drive magnetic ux through magnetic circuit, a magneto motive force (mmf) is necessary. Magnetomotive force can be produced when current ows in a coil of one or more turns. The magnitude of mmf is directly proportional to the current I and number of turns of the coil N,

Magnetomotive Force (MMF)

Reluctance

Magnetomotive Force (MMF)The current owing in the electrical circuit due to the existence of electromotive force(emf) across the circuit To drive magnetic ux through magnetic circuit, a magneto motive force (mmf) is necessary. Magnetomotive force can be produced when current ows in a coil of one or more turns. The magnitude of mmf is directly proportional to the current I and number of turns of the coil N, mmf = NI

Magnetomotive Force (MMF)

Reluctance

Magnetomotive Force (MMF)The current owing in the electrical circuit due to the existence of electromotive force(emf) across the circuit To drive magnetic ux through magnetic circuit, a magneto motive force (mmf) is necessary. Magnetomotive force can be produced when current ows in a coil of one or more turns. The magnitude of mmf is directly proportional to the current I and number of turns of the coil N, mmf = NI If the magnetic circuit of magnetic material is homogeneous and of uniform cross sectional area, the magnetomotive force per meter length of the magnetic circuit (path of magnetic ux) is called the magnetic eld strength (H).

Magnetomotive Force (MMF)

Reluctance

Magnetomotive Force (MMF)The current owing in the electrical circuit due to the existence of electromotive force(emf) across the circuit To drive magnetic ux through magnetic circuit, a magneto motive force (mmf) is necessary. Magnetomotive force can be produced when current ows in a coil of one or more turns. The magnitude of mmf is directly proportional to the current I and number of turns of the coil N, mmf = NI If the magnetic circuit of magnetic material is homogeneous and of uniform cross sectional area, the magnetomotive force per meter length of the magnetic circuit (path of magnetic ux) is called the magnetic eld strength (H). mmf H= l

Magnetomotive Force (MMF)

Reluctance

Reluctance

Magnetomotive Force (MMF)

Reluctance

Reluctance

I

Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area

Magnetomotive Force (MMF)

Reluctance

Reluctance

I

Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba

Magnetomotive Force (MMF)

Reluctance

Reluctance

I

Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba

Magnetomotive Force (MMF)

Reluctance

ReluctanceAlso, mmf = magnetic eld strength length of ux path mmf = Hl

I

Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba

Magnetomotive Force (MMF)

Reluctance

ReluctanceAlso, mmf = magnetic eld strength length of ux path mmf = Hl Taking ratio of and mmf, Ba = mmf Hl B But, = = 0 r H

I

Magnetomotive Force (MMF)

Reluctance

ReluctanceAlso, mmf = magnetic eld strength length of ux path mmf = Hl Taking ratio of and mmf, Ba = mmf Hl B But, = = 0 r H a mmf l = 0 r or = mmf l 0 r a Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba

I

Magnetomotive Force (MMF)

Reluctance

ReluctanceAlso, mmf = magnetic eld strength length of ux path mmf = Hl Taking ratio of and mmf, Ba = mmf Hl B But, = = 0 r H a mmf l = 0 r or = mmf l 0 r a Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba For the electric circuits, emf l =R= current a

I

Magnetomotive Force (MMF)

Reluctance

ReluctanceAlso, mmf = magnetic eld strength length of ux path mmf = Hl Taking ratio of and mmf, Ba = mmf Hl B But, = = 0 r H a mmf l = 0 r or = mmf l 0 r a Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba For the electric circuits, emf l =R= current a As emf/current is called resistance in electric circuits, mmf/ux can be termed as reluctance for magnetic circuits.

I

Magnetomotive Force (MMF)

Reluctance

ReluctanceAlso, mmf = magnetic eld strength length of ux path mmf = Hl Taking ratio of and mmf, Ba = mmf Hl B But, = = 0 r H a mmf l = 0 r or = mmf l 0 r a Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba For the electric circuits, emf l =R= current a As emf/current is called resistance in electric circuits, mmf/ux can be termed as reluctance for magnetic circuits. Reluctance is the property of magnetic material which opposes the ow of ux through it.

I

Magnetomotive Force (MMF)

Reluctance

ReluctanceAlso, mmf = magnetic eld strength length of ux path mmf = Hl Taking ratio of and mmf, Ba = mmf Hl B But, = = 0 r H a mmf l = 0 r or = mmf l 0 r a Let the ring have a mean circumference of l meter, a cross-sectional area of a m2 and N turns carrying a current of I ampere, then the total ux owing in the dotted path is given by, = ux density cross sectional area = Ba For the electric circuits, emf l =R= current a As emf/current is called resistance in electric circuits, mmf/ux can be termed as reluctance for magnetic circuits. Reluctance is the property of magnetic material which opposes the ow of ux through it. Reluctance R = l ampere/weber 0 r a

I

Magnetomotive Force (MMF)

Reluctance

Laws of Magnetic Circuits

Magnetomotive Force (MMF)

Reluctance

Laws of Magnetic CircuitsOhms law for electric circuit is, emf = current resistance or E = I R Ohms law for magnetic circuit is, mmf = ux reluctance or mmf = S

Magnetomotive Force (MMF)

Reluctance

Laws of Magnetic CircuitsOhms law for electric circuit is, emf = current resistance or E = I R Ohms law for magnetic circuit is, mmf = ux reluctance or mmf = S 1 length l = conductivity area a 1 length 1 l = permeability area 0 r a

For electric circuits, Resistance =

For magnetic circuits, Reluctance =

Magnetomotive Force (MMF)

Reluctance

Laws of Magnetic CircuitsOhms law for electric circuit is, emf = current resistance or E = I R Ohms law for magnetic circuit is, mmf = ux reluctance or mmf = S 1 length l = conductivity area a 1 length 1 l = permeability area 0 r a

For electric circuits, Resistance =

For magnetic circuits, Reluctance =

In series electric circuits, the total resistance of the circuit is equal to the sum of all the resistance in series. Similarly, when the ux has to permeate a number of portions of a magnetic circuit in series, the total reluctance of the complete magnetic circuit will be equal to the sum of the reluctances of various portions, i.e. S = S1 + S2 + S3 +

Magnetomotive Force (MMF)

Reluctance

Laws of Magnetic