MAGNETIC CIRCUITS

COURSE SYLLABUS

I. Department: ELECTRICAL AND ALLIED DEPARTMENT

II. Course Code: EE 3 / EE3L

III. Course Title: Electromechanical Energy Conversion

IV. Course Description:

The course covers engineering aspects and application of transformers, induction motors, synchronous generators and motors, direct current generators and motors.

V. Course objectives:

At the end of the course, the students shall be able to ;
a. Develop the applied theories of magnetic circuits, the difference between the magnets and electromagnetism.
b. Learn the different electromechanical system of producing electrical energy.
c. Impart the applied theories, principles and performance characteristics of DC and AC machines and solve problems involving DC and Ac machines.
d. Apply gained knowledge for the advancement of mankind.

VI. Unit Credit/Time:

3 units lec (3.75 hrs)
1 unit lab (3.75 hrs)
LECTURE:
LABORATORY:

VII. Semester/Term Offered: 3rd year/first term

VIII. Pre-requisite Subject/s: EE1/EE1L

IX. Co-requisite Subject/s:

X. Clientele: BSEE Straight Engineering Students

XI. Requirements:

The requirements of this course and the corresponding inputs into the final grade are as follows:
a. quizzes, seatworks, assignments, recitation, attendance.................20%
b. unit test and actual exercises.........................................................25%
c. term test........................................................................................20%
d. laboratory.....................................................................................35%
TOTAL ............................................................................................100%

XII. Textbooks:
Electric Machinery and power Systems Fundamentals

XIII. References:
Electric Motor Handbook By: Beaty, 1998
Electrical Machines by Charles Siskind
Fundamentals of Electric Machines copyright 2005

MAGNETIC CIRCUITS

A magnetic circuit is made up of one or more closed loop paths containing a magnetic flux. The flux is usually generated by permanent magnets or electromagnets and confined to the path by magnetic cores consisting of ferromagnetic materials like iron, although there may be air gaps or other materials in the path. Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads.

The concept of a "magnetic circuit" exploits a one-to-one correspondence between the equations of the magnetic field in a non-hysteretic material to that of an electrical circuit. Using this concept the magnetic fields of complex devices such as transformers can be quickly solved using the methods and techniques developed for electrical circuits.

Some examples of magnetic circuits are:

• horseshoe magnet with iron keeper (low-reluctance circuit)
• horseshoe magnet with no keeper (high-reluctance circuit)
• electric motor (variable-reluctance circuit)

Magnetomotive force (MMF)

EMF drives a current of electrical charge in electrical circuits, magnetomotive force (MMF) 'drives' magnetic flux through magnetic circuits. The term 'magnetomotive force', though, is a misnomer since it is not a force nor is anything moving. It is perhaps better to call it simply MMF. In analogy to the definition of EMF, the magnetomotive force around a closed loop is defined as:

The MMF represents the potential that a hypothetical magnetic charge would gain by completing the loop. The magnetic flux that is driven is not a current of magnetic charge; it merely has the same relationship to MMF that electrical current has to EMF.

The unit of magnetomotive force is the ampere-turn (At), represented by a steady, direct electric current of one ampere flowing in a single-turn loop of electrically conducting material in a vacuum. The gilbert (Gi), established by the IEC in 1930 [1], is the CGS unit of magnetomotive force and is a slightly smaller unit than the ampere-turn. The unit is named after William Gilbert (1544–1603) English physician and natural philosopher.

The magnetomotive force can often be quickly calculated using Ampere's law. For example, the magnetomotive force of long coil is:

,

where N is the number of turns and I is the current in the coil. In practice this equation is used for the MMF of real inductors with N being the winding number of the inducting coil.