Product Manual

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CHAPTER I
Electric Motor History and Principles
The electric motor in its simplest terms is a converter of electrical
energy to useful mechanical energy. The electric motor has played a
leading role in the high productivity of modern industry, and it is there-
fore directly responsible for the high standard of living being enjoyed
throughout the industrialized world.
The beginnings of the electric motor are shrouded in mystery, but this
much seems clear: The basic principles of electromagnetic induction
were discovered in the early 1800’s by Oersted, Gauss and Faraday, and
this combination of Scandinavian, German and English thought gave us
the fundamentals for the electric motor. In the late 1800’s the actual
invention of the alternating current motor was made by Nikola Tesla, a
Serb who had migrated to the United States. One measure of Tesla’s
genius is that he was granted more than 900 patents in the electrical
field. Before Tesla’s time, direct current motors had been produced in
small quantities, but it was his development of the versatile and rugged
alternating current motor that opened a new age of automation and
industrial productivity.
An electric motor’s principle of operation is based on the fact that a
current-carrying conductor, when placed in a magnetic field, will have a
force exerted on the conductor proportional to the current flowing in the
conductor and to the strength of the magnetic field. In alternating current
motors, the windings placed in the laminated stator core produce the
magnetic field. The aluminum bars in the laminated rotor core are the
current-carrying conductors upon which the force acts. The resultant
action is the rotary motion of the rotor and shaft, which can then be
coupled to various devices to be driven and produce the output.
Many types of motors are produced today. Undoubtedly, the most
common are alternating current induction motors. The term “induc-
tion” derives from the transference of power from the stator to the
rotor through electromagnetic induction. No slip rings or brushes are
required since the load currents in the rotor conductors are induced by
transformer action. The induction motor is, in effect, a transformer - with
the stator winding being the primary winding and the rotor bars and end
rings being the movable secondary members.
Both single-phase and polyphase (three-phase) AC motors are
produced by LEESON and many other manufacturers. In polyphase