Magnetism - The Power of Attraction and Repulsion
By: Thomas Yoon
Undoubtedly, the most important property in the operation of electrical equipment is electromagnetism. It's the property of attraction and repulsion that enables motors, generators, solenoids, relays and other control equipment to function.
Magnets can be classified as permanent or temporary by their ability to retain the magnetism. Normally, hardened steel or nickel-cobalt alloys are able to retain their magnetism indefinitely. These are called permanent magnets. In the electrical industry, they
find many applications. Some of them are: electric meters, magnetos, loudspeakers, and control switches. Because of its permanent nature, there are also many other uses not related to industry.
The bulk of the uses in electrical equipment are the temporary magnets. When electrical direct current is passed through a coil surrounding a soft iron core, the latter becomes a magnet. When the current is removed, the coil loses its magnetism. Solenoid
actuators and relays make use of this phenomenon to control circuits and other processes.
However, not all the magnetism is lost. A small part of the magnetism still remains after the magnetizing force is removed. To counter this effect, some of the magnetic cores are modified to reduce the effect of these remaining magnetism. By enlarging the air
gaps for some of the magnetic components, the forces coming from the small magnetism are rendered too weak to counter the forces of springs found in solenoid actuators and relays.
But this remaining magnetism, called residual magnetism, is important for the operation of DC generators. Electrical current is generated or induced in a wire only when there is a movement relative to the magnetism. So without that first residual magnetism,
there will not be any current induced.
In fact, to start an electrical generator for the very first time, some magnetism must be present in the steel cores before it can produce electricity by itself. Usually, the current will be injected in from electrochemical storage batteries. Once the
generator is able to produce power by itself, some of it is fed back to the magnetic core to maintain that magnetism. Only when the soft steel core has acquired the residual magnetism, can the generator produce electricity each time it is started.
Understanding magnetic fields can enable us to design powerful electrical machines that can be used for the good of mankind. Where can it lead us? Perhaps to wonder!
Our mother earth itself is a giant magnet with its own North Pole and South Pole, where world travelers using magnetic compasses are able to determine their location relative to them. Where are we in relation to attraction and repulsion of planets in the
universe? Is it magnetism? Is it gravity?
Until next time...
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