Week05 Chapter 2 Electromagnetism and Magnetic Circuit

8/12/2019 Week05 Chapter 2 Electromagnetism and Magnetic Circuit

1/25

CHAPTER 2

Electromagnetism and magnetic circuit

5thweek

Introduction, Understanding of magnetic fields,

magnetic relationship


2/25

2

MagnetismObjective of the

chapterUnderstanding concept basic magnetic field,magnetic flux, magnetic force at the conductor,solenoid and toroid

Identify force on the conductor carryingcurrent in the magnetic field

Identify direction of induce emf on the

conductor in the magnetic field


3/25

3

Objective of the chapter (Cont.)

Relationship between magnetic and electrical

circuit

Understanding magnetic characteristics and to

analysis simple magnetic circuit

Understanding concept self, mutual and

coupling coefficiences


4/25

4

Potential to attract other material

Pure, permanence and temporary

magnet

Pure From earth

Permanence

Depended on metal Temporary

electromagnetic

Magnetic material


5/25

5

Two pole, north and south

Direction of line force outside magnetic material

as shown in figure 2.1

figure 2.1

Magnetic material (Cont.)


6/25

6

Field Detector can use acompass to map out magneticfield, as shown in (Figure 2.2)

Field forms closed flux linesaround the magnet

Magnetic flux measured inWebers (Wb)

Symbol

Figure 2.2

Magnetic Field/flux


7/25

7

Magnetic flux lines are assumed to have the following

properties: Leave the north pole (N) and enter the

south pole (S) of a magnet

Like magnetic poles repel each other asshown in figure 2.3 (a)

Unlike magnetic poles create a force ofattraction as shown in figure 2.3 (b)

Magnetic lines of force (flux) areassumed to be continuous loops

Flux lineshort distance

Magnetic Flux or flux line


8/25

8

Figure 2.3(a) (b)

Properties of magnetism


9/25

9

Magnetic Field on Conductor

A magnetic field also forms

round a conductor along

which a current is flowing

Field can be described using

right hand screw rule


10/25

10

Magnetic Circuit

Flux

Force line in the magnetic field

Symbol, Weber (Wb)


11/25

11

Flux Density

Area,

Flux,


12/25

12

Magnetomotive Force (mmf)

Coil generates magnetic field in ferrous toroid

Driving Magnetomotive Force (mmf)is neededto overcome toroid reluctance

mmf, proportional to current, I and number of turn, N

mmf = NI, Ampere-turn (AT)


13/25

13

Magnetic field

intensity/strength Magnetic field strength or Magnetizing force

mmf per length

l

NI

l

mmfH , Unit, At/m


14/25

14

Permeability

Permeability is a measure of the ease by which amagnetic flux can pass through a material

(Wb/Am)

Permeability of free space o= 4 x 10-7(Wb/Am)

Permeability:

= absolute permeability

o= free space permeability

r= relatif permeability= or

gforcemagnetizin

yfluxdensit

H

B

B = H= orH


15/25

15

Permeability depend on the material

free space

0= 4 x 10-7(Wb/Am)

Non-magnetic materil i.e. air, vacuum etc

Relative = r= 1


16/25

16

Reluctance

Reluctance: resistance to flow of magnetic flux

Where,

llength

Across section area

- Permeability

SymbolS

unitAT/Wb or Siemen

Associated with magnetic circuit

flux equivalent to current in electric circuit

A

lS

A

l

r0


17/25


18/25

18

Magnetic leakage and Fringing

Fringing

Occurs at the air gap

Flux intends to bulge outwards

Increasing the effective area Reduce the flux density

As shown in Figure 2.a

(still useful flux)


19/25

19


20/25

20


21/25


22/25


23/25

23


24/25

24


25/25

25

Documents

Week05 Chapter 2 Electromagnetism and Magnetic Circuit