magnetic hysteresis eee (2)

8/12/2019 Magnetic Hysteresis EEE (2)

1/32


2/32

Group Vsub: ELEMENTS OF ELECTRICAL ENGINEERINGCode:2110005

Part of active learning assignment

1. Ankit Makwana 13BEEEN0852. Dhaval Darji 13BEEEG1223. Parth Tank 13BEEEG0654. Biren Panchal 13BEEEG099


3/32

Magnetization or B-H Curve


4/32

The set of magnetization curves, M above

represents an example of the relationshipbetween B and H for soft-iron and steelcores.

Every type of core material will have itsown set of magnetic hysteresis curves.

The flux density increases in proportion tothe field strength until it reaches a certain

value were it can not increase any more .


5/32

This is because there is a limit to the amount offlux density that can be generated by the coreas all the domains in the iron are perfectlyaligned.

Any further increase will have no effect on the

value of M, and the point on the graph wherethe flux density reaches its limit iscalled Magnetic Saturation also knownas Saturation of the Core


6/32

Magnetic Hysteresis Loop


7/32

The Magnetic Hysteresis loop above, shows thebehavior of a ferromagnetic core graphically .

The relationship between B and H is non-linear. An unmagnetised core both B and H will be atzero, point 0 on the magnetization curve.

If the magnetization current, i is increased in apositive direction to some value the magnetic fieldstrength H increases linearly with i and the fluxdensity B will also increase as shown by the curvefrom point 0 to point a towards saturation.


8/32

Now if the magnetizing current in the coil is

reduced to zero the magnetic field around the corereduces to zero but the magnetic flux does not reachzero due to the residual magnetism present withinthe core and this is shown on the curve frompoint a to point b.

To reduce the flux density at point b to zero weneed to reverse the current flowing through thecoil. The magnetizing force which must be applied

to null the residual f lux density is called a"Coercive Force". This coercive force reverses themagnetic field re-arranging the molecularmagnets until the core becomes unmagnetised atpoint c.


9/32

. An increase in the reverse current causes the core

to be magnetized in the opposite direction andincreasing this magnetization current will causethe core to reach saturation but in the oppositedirection, point d on the cure which is symmetrical

to point b.

If the magnetizing current is reduced again to zero

the residual magnetism present in the core will beequal to the previous value but in reverse atpoint e.


10/32

Again reversing the magnetizing current flowing

through the coil this time into a positive direction will cause the magnetic flux to reach zero,point f on the curve and as before increasing themagnetization current further in a positivedirection will cause the core to reach saturation atpoint a.

Then the B-H curve follows the path of a-b-c-d-e-

f-a as the magnetizing current flowing through thecoil alternates between a positive and negative value such as the cycle of an AC voltage. This pathis called a Magnetic Hysteresis Loop .


11/32

Coercively and Remanence

in Permanent Magnets


12/32

A good permanent magnet should produce a highmagnetic field with a low mass, and should be stableagainst the influences which would demagnetize it.The desirable properties of such magnets are typicallystated in terms of the Remanence and Coercivity ofthe magnet materials.

When a Ferromagnetic material is magnetized inone direction, it will not relax back to zero

magnetization when the imposed magnetizing field isremoved. The amount of magnetization it retains atzero driving field is called its Remanence.


13/32

It must be driven back to zero by a field in the

opposite direction; the amount of reverse drivingfield required to demagnetize it is called itscoercivity.

The table below contains some data aboutmaterials used as permanent magnets. Both thecoercivity and remanence are quoted in Tesla, thebasic unit for Magnetic field B . The hysteresisloop above is plotted in the formof Magnetization M as a function ofdriving magnetic Field strength H .


14/32


15/32

Hysteresis Loss

Due to presence of magnetic hysteresis afraction of applied power will be lost in the

form of heat.

The portion of power lost corresponds to

the difference between the energy storedand energy returned back by the magneticcore .This is called Hysteresis loss .


16/32

Other Definition OF Hysteresis Loss


17/32

If the magnetic field applied to a magnetic

material is increased and then decreased back toits original value, the magnetic field inside thematerial does not return to its original value.

The internal field 'lags' behind the external field.This behaviour results in a loss of energy, calledthe hysteresis loss, when a sample is repeatedly

magnetized and demagnetized.

. The materials used in transformer cores andelectromagnets are chosen to have a low hysteresisloss.


18/32

Factor Affecting The Hysteresis Loss

Frequency of Magnetization.

Volume of the Material.

Area enclosed by the Hysteresis Loop.

Area of the Hysteresis Loss : The Hysteresis Loss isdirectly Proportional to the area under theHysteresis Loop . For the loss materials the

Hysteresis Loop is narrow.


19/32


20/32

The area and the shape of the magneticmaterial are the important parameters

which decide the suitability of a material for

a particular application.

In the Hysteresis Loop of Soft

Ferromagnetic material all the valuessuch as residual magnetism and coerciveforce are moderate . Hence this material is

used for making the electromagnets.


21/32

In the Hysteresis Loop of HardFerromagnetic material all the valuessuch as residual magnetism and coerciveforce are Large . Hence this material is usedfor making the permanent magnet.


22/32

Variations in Hysteresis Curves


23/32


24/32


25/32

Soft magnets (low coercivity) are used ascores in electromagnets .

The low coercively reduces that energy lossassociated with hysteresis.


26/32

Other Application of Magnetic Hysteresis

Magnetic hysteresis brakes usepermanent magnets surrounding a

hysteresis disc to provide a constant torque, without external power.

By varying the displacement of themagnetic hysteresis disk, this torque can bequickly adjusted by a machine operator.


27/32

The magnetic brakes are ideally suited to control winding applications in the wire, cable andconverting industries and anywhere a constanttorque is required.


28/32

Magnetic tape

Quarter-Inch Cartridges


29/32


30/32

The reverse side of a typical credit card1-Magnetic Stripe2-Signature Strip3-Card SecurityCode


31/32


32/32

Thank you

magnetic hysteresis eee (2)

Documents