Generac Power Systems 941-2 Section GENERATOR FUNDAMENTALS, Magnetism, Electromagnetic Fields

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GENERATOR FUNDAMENTALS

MAGNETISM

Magnetism can be used to produce electricity and electricity can be used to produce magnetism.

Much about magnetism cannot be explained by our present knowledge. However, there are certain pat- terns of behavior that are known. Application of these behavior patterns has led to the development of gen- erators, motors and numerous other devices that uti- lize magnetism to produce and use electrical energy.

See Figure 1. The space surrounding a magnet is permeated by magnetic lines of force called "flux". These lines of force are concentrated at the magnet's north and south poles. They are directed away from the magnet at its north pole, travel in a loop and re- enter the magnet at its south pole. The lines of force form definite patterns which vary in intensity depend- ing on the strength of the magnet. The lines of force never cross one another. The area surrounding a magnet in which its lines of force are effective is called a "magnetic field".

Like poles of a magnet repel each other, while unlike poles attract each other.

NOTE: The "right hand rule" is based on the "cur- rent flow" theory which assumes that current flows from positive to negative. This is opposite the "electron" theory, which states that current flows from negative to positive.

Figure 2. The Right Hand Rule

Figure 1. Magnetic Lines of Force

ELECTROMAGNETIC FIELDS

All conductors through which an electric current Is flowing have a magnetic field surrounding them. This field is always at right angles to the conductor. If a compass is placed near the conductor, the compass needle will move to a right angle with the conductor. The following rules apply:

•The greater the current flow through the conductor, the stronger the magnetic field around the conductor.

•The increase in the number of lines of force is directly proportional to the increase in current flow and the field is distributed along the full length of the conductor.

•The direction of the lines of force around a conduc- tor can be determined by what is called the "right hand rule". To apply this rule, place your right hand around the conductor with the thumb pointing in the direction of current flow. The fingers will then be pointing in the direction of the lines of force.

ELECTROMAGNETIC INDUCTION

An electromotive force (EMF) or voltage can be pro- duced in a conductor by moving the conductor so that it cuts across the lines of force of a magnetic field.

Similarly, if the magnetic lines of force are moved so that they cut across a conductor, an EMF (voltage) will be produced in the conductor. This is the basic principal of the revolving field generator.

Figure 3, below, illustrates a simple revolving field generator. The permanent magnet (Rotor) is rotated so that its lines of magnetic force cut across a coil of wires called a Stator. A voltage is then induced into the Stator windings. If the Stator circuit is completed by connecting a load (such as a light bulb), current will flow in the circuit and the bulb will light.

Figure 3. A Simple Revolving Field Generator

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