Lecture 01 Electro Mechanical System 1

Electro-Electro-Mechanical Mechanical

SystemSystem

Course: Electro-Mechanical Systems

Lecture 01 Electro Mechanical System 2

Instructor: Shahid Anwar

Text Book: Electrical Machines, Drives,and Power

SystemAuthor: Theodore Wildi

(6th Edition)Publisher: Pearson Education

Brief Description:

Lecture 01 Electro Mechanical System 3

Course is designed to provide students with an understanding of:

Working of transformers;The general principles of electromechanical machine operation, rotating magnetic fields, and power conversion;Design process for sizing, powering and controlling rotational machines;Methods for calculating and measuring machine parameters;A general overview of variable speed and dc machine drives

Lecture 01 Electro Mechanical System 4

Chapter 2Chapter 2Fundamentals of Fundamentals of

MagnetismMagnetism

Magnetic Field

Lecture 01 Electro Mechanical System 5

Whenever a magnetic flux exists in a conductor or component, it is due to the presence of a magnetic field intensity H, given by: H = U/l

Where: H = magnetic field intensity [A/m] U = magnetomotive force acting on the

component [A] or (ampere turns)

l = length of the magnetic circuit [m]

Magnetic Flux Density

Lecture 01 Electro Mechanical System 6

For a magnetic flux , there exists a magnetic flux density, B, given by B = /A

Where: B = flux density [T] (tesla) = flux in a component [Wb] (weber) A = cross section area [m2]

B-H curve in vacuum

Lecture 01 Electro Mechanical System 7

In free space, the magnetic flux density B is directly proportional to the magnetic field intensity H and is given by: B = µoH

The constant of proportionality for free space is called the permeability constant, µo

µo = 4x10-7 H/m [henry/meter] (also called permeability of vacuum.)

Lecture 01 Electro Mechanical System 8

The flux density is influenced by the magnetic property of the material in which the flux passes instead of

specifying a permeability for every material, a relative permeability is defined, µr = µ / µo

relative permeability is unitless

B = µoµrH

for many materials, the relative permeability is not constant but varies nonlinear w.r.t. flux density B

Determining Relative Permeability

Lecture 01 Electro Mechanical System 9

Determining Relative Permeability

ExampleDetermine the relative

permeability of relay steel (1% silicon) at a flux density of 1.4 T requires a magnetic field strength of 1000 A/m

One can find the relative permeability in a material by taking the ratio of the flux density in the material to the flux density that would have been produced in free-space.

H

B

H

Br 000,800

0

11201000

4.1000,800 r

Determining Relative Permeability

Lecture 01 Electro Mechanical System 10

Following diagram shows the saturation curves of a broad range of materials from vacuum to permalloy, one of the most permeable magnetic material known