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Alternating Current Motors and Generators
A.
Bhatia
Overview
An alternating current generator, or AC generator, produces an
alternating current, which means the voltage produced alternately reverses from
positive to negative polarity, producing a corresponding change in the direction
of current flow. Much like a DC generator, an AC generator requires a coil to
cut across the force lines of a magnetic field. This coil is attached to two
slip rings, which deliver the current to and from the load destination, thus
completing the circuit. Alternating current generators are often called
“Alternators”.
The
magnitude of AC voltage generated by an AC generator is dependent on:
(1) The strength of the magnetic field (number of lines of force)
(2) The speed at which the loop rotates
(3) The number of loops of wire that cut the magnetic field.
A rotation speed of 3000 revolutions per minute(RPM) produces 50
Hz, and 3600 RPM produces 60 Hz.
The electric current in North American homes has a frequency of 60 hertz, while
in Europe it is 50 Hz.
An alternating current motor, or AC motor uses electrical energy
to produce motion and torque. Very simple AC motors are called "Squirrel cage
motors"; these have only one or more stationary coils within which a special
kind of mechanical rotor is free to rotate. There is no electrical connection to
the rotor from the outside. Most AC motors require a starter, or method of
limiting the inrush current to a reasonable level. Types of motor starting
include reactive (capacitor start and inductive start), and electronic
(frequency drives and soft start drives). The reactive start method is usually
used on fractional horsepower motors, and the electronic method is usually
reserved for larger motors.
This
4-hr course provides a basic understanding of AC motors and generators,
explaining how to use them, how to calculate power, and determine torque
considerations. The course is
based
entirely on Naval Education and Training Materials (NAVEDTRA
14177),
Electricity and Electronic Training Series;
Module-5 and covers Chapter 3 and 4 titled “Alternating Current
Generators and Alternating Current Motors”.
The student must take a multiple-choice quiz consisting of
twenty (20) questions at the end of
this course to obtain PDH credits.
Specific Knowledge or Skill Attained
This course teaches the following specific knowledge and
skills:
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The
principle of magnetic induction as it applies to AC generators.
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The
differences between the two basic types of AC generators.
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The
factors that determine the maximum power output of an AC generator.
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The
relationships between the individual output and resultant vectorial sum
voltages in multiphase generators.
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The
factors that determine the frequency and voltage of the alternator output.
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The
purpose and procedure of parallel generator operation.
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Three
basic types of AC motors and the characteristics of each type.
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The
characteristics of a series motor that enable it to be used as a universal
motor.
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The
primary application of synchronous motors, and the characteristics that make
them suitable for that application.
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The
features that make the AC induction motor the most widely used of electric
motors.
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The
operation of split-phase windings in single-phase AC induction motors.
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The
effects of shaded poles in single-phase, AC induction motors.
Course
Click on the following PDF attachment and review the document " prior to taking a quiz for
PDH credit.
Alternating Current Motors and Generators (415 KB)
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credit. Click on the link below.
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