Magnetic permeability and the b/h curve, Electrical Engineering

Magnetic permeability and the B/H curve

To measure the relationship between field strength H and flux density B for a material, a sample is made into a closed ring and a magnetising coil wound onto it. Current flowing in this coil creates a m.m.f. equal to NI which in turn produces a magnetic field

H= NI/L

in the ring. So  H is proportional to the current in the energising coil and may be obtained from direct measurement of I. If a change in the current occurs, the flux density changes and this will induce a transient 'back e.m.f' in a second coil that is also wound onto the ring.

 

1372_Magnetic permeability and the B-H curve.png

 

The integral of the back emf is proportional to B. Hence the relationship between B and H may be determined from measurement of I (to give H) and the induced back e.m.f in the coils (to give B).

The result of such measurements on various materials produces two types of curves - straight lines of low

B/H =µr

values and curves for  which the value of B/H =µr   varies. This first type are sub divided into paramagnetic
varies. This first type are sub divided into paramagnetic materials if B/H =µr >1 and diamagnetic if B/H =µr <1. The second type are ferromagnetic and have a more complicated dependence of B on H.  At low H these have B/H =µ>>1 (typically 100 - 100000)

85_Magnetic permeability and  B-H curve.png

 

 

It is also found that ferromagnetic materials lose these high µr properties above a well-defined temperature (different for different materials) known as the Curie temperature. This typically  r ranges from 200 - 750 °C and limits the maximum temperature that many electromagnetic devices can operate.


The temperature dependence of the ferromagnetic properties give a clue to the physical reason for the different

permeabilities of the materials. Diamagnetic and paramagnetic properties are attributable to the orbiting electrons within the atoms of the material. Ferromagnetic properties arise due to the orientation of atoms on a macroscopic scale so that the magnetic fields created by the orbiting electrons within each atom reinforce each other. These 'domains' of high magnetic strength may contain ~10-12   atoms each. The domains are initially randomly directed but under the influence of an external magnetic field, re-orientate to point in the same direction. Initially this is along the direction of the nearest crystal axis to the direction of the magnetic field.

 

Steadily increasing the external field brings them directly into line with the external field direction.If the external field is now removed, the domains relax back to point in the nearest crystal direction, leaving a residual magnetism. Materials that have a strong residual magnetism are used for permanent magnets. Cycling the current over one complete cycle produces a hysteresis B/H curve

 

 

 

1726_hysteresis B-H curve.png

Posted Date: 8/22/2012 5:56:39 AM | Location : United States







Related Discussions:- Magnetic permeability and the b/h curve, Assignment Help, Ask Question on Magnetic permeability and the b/h curve, Get Answer, Expert's Help, Magnetic permeability and the b/h curve Discussions

Write discussion on Magnetic permeability and the b/h curve
Your posts are moderated
Related Questions
For the 3-bit 2 n -R D/A converter of Figure, calculate the analog output voltage when the input is (a) 100, and (b) 010. Solution a. For the binary input 100, switches con


Q. What is a clipper circuit? Clipping circuits are linear wave shaping circuits. The main function of 'clipper' is that it clips off a part of input waveform i.e., it cut off

what are the disadvantages of superposition theorem?

The following data apply to a 100-kW, 250-V, six-pole, 1000-r/min long-shunt compound generator: no-load rotational losses 4000 W, armature resistance at 75°C = 0.015 , series-fie

Turn off Time This is also known  as gate controlled  turn on  time. The time  interval between  a specified  point at the beginning  of the  gate pulse  and the  instant wh


• Vectors can be represented in terms of basis vectors, a set of vectors that span the vector space • Mostly will use i, j, k to denote a Cartesian right-handed basis set • V

Binary Multiplication Multiplication can be seen as multiple additions. For  example  if we  have to multiple 4 and 8 we can  8, 4  time to get the  solution. Actually this  conc

Get the equivalent inductance at terminal in circuit: Acquire the equivalent inductance at terminal AB in circuit shown in Figure. Solution Inductances also follow the