EEC 123 Electrical Machiens I Lecture Note Pdf Download
TABLE OF CONTENT
Subject Electrical Machines I
Course Code EEC123
Credit Hours 6
Week 1 : EEC 123 Electrical Machiens I Lecture Note Pdf Download
Now, before we discuss basic electrical machine operation a short review of
magnetism might be helpful to many of us. We all know that a magnet will attract and
hold metal objects when the object is near or in contact with the magnet.
1.2 Concepts of Magnetism
A magnetic field is a change in energy within a volume of space. The magnetic
field surrounding a bar magnet can be seen in the magnetograph shown in fig.(1-1). A
magnetograph can be created by placing a piece of paper over a magnet and sprinkling
the paper with iron filings. The particles align themselves with the lines of magnetic
force produced by the magnet. The magnetic lines of force show where the magnetic
field exits the material at one pole and reenters the material at another pole along the
length of the magnet. It should be noted that the magnetic lines of force exist in three dimensions but are only seen in two dimensions in the image.
It can be seen in the magnetograph that there are poles all along the length of the
magnet but that the poles are concentrated at the ends of the magnet. The area where the exit poles are concentrated is called the magnet’s north pole and the area where the entrance poles are concentrated is called the magnet’s south pole.
Magnets come in a variety of shapes and one of themore common is the horseshoe (U) magnet.
The horseshoe magnet has north and south poles just like a bar magnet but the magnet is curved so the poles lie in the same plane, the magnetic field is concentrated between the poles as shown in figure (1-2).
The number of magnetic lines of force is a known as magnetic flux Φ. The flux
has the weber (wb) as its unit, The number of magnetic lines of force cutting through a plane of a given area at a right angle is known as the magnetic flux density B.
The flux density or magnetic induction has the tesla as its unit. One tesla is equal to 1
Newton/(A/m). From these units it can be seen that the flux density is a measure of the force applied to a particle by the magnetic field. T