Print this page AC Alternators and Motors
Lee Layton, P.E.
Course Outline
This course is divided into two chapters. Chapter one covers AC alternators and begins with an overview of a basic AC alternator. The course then moves from a basic AC alternator to several types of practical AC alternators. Single-phase, two-phase, and three-phase alternators are discussed in detail, including different types of three-phase connections. Other items, such as frequency, voltage regulation, and AC voltage control are also covered. Chapter two, covering AC motors, begins with a review of a series AC motor. Rotating magnetic fields are discussed for different types of motors. Both induction and synchronous AC motors are explained.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
After taking this course you should be able to:
- Describe the principle of magnetic induction as it applies to AC generators;
- Describe the differences between the two basic types of AC generators;
- List the advantages and disadvantages of the two types of AC generators;
- Explain the operation of multiphase AC generators and compare with single-phase;
- Explain, using diagrams, the different methods of connecting three-phase alternators and transformers;
- Describe the characteristics of a series motor that enable it to be used as a universal motor;
- Explain the relationships of the individual phases of multiphase voltages as they produce rotating magnetic fields in AC motors;
- Describe the placement of stator windings in two-phase, AC motors using rotating fields;
- State the primary application of synchronous motors, and explain the characteristics that make them suitable for that application;
- Describe the features that make the AC induction motor the most widely used of electric motors;
- Explain the operation of split-phase windings in single-phase AC induction motors; and
- Describe the effects of shaded poles in single-phase, AC induction motors.
Intended Audience
This course is intended for electrical engineers and others who want to understand how AC generators and motors operate.
Benefit to Attendees
The generation and consumption of power for useful work is based on converting another fuel source into electricity and then using an electric motor to perform the work. This course explains how both AC generators and motors work along with the advantages and disadvantages of these devices.
Course Introduction
An Alternating Current generator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current. Most generators use a rotating magnetic field with a stationary armature.
Alternating current generating systems were known in simple forms from the discovery of the magnetic induction of electric current. Michael Faraday developed the "rotating rectangle", where each active conductor passed successively through regions where the magnetic field was in opposite directions.
Alternators generate electricity using the same principle as DC generators, namely, when the magnetic field around a conductor changes, a current is induced in the conductor. Typically, a rotating magnet, called the rotor turns within a stationary set of conductors wound in coils on an iron core, called the stator. The field cuts across the conductors, generating an induced EMF (electromotive force), as the mechanical input causes the rotor to turn.
The rotating magnetic field induces an AC voltage in the stator windings. Often there are three sets of stator windings, physically offset so that the rotating magnetic field produces a three phase current, displaced by one-third of a period with respect to each other.
The rotor's magnetic field may be produced by induction (as in a "brushless" alternator), by permanent magnets (as in very small machines), or by a rotor winding energized with direct current through slip rings and brushes. The rotor's magnetic field may even be provided by stationary field winding, with moving poles in the rotor.
Course Content
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Course Summary
The AC generator is the most important means of producing electrical power. AC generators range in size from a few watts to many mega-watts. In this course, we have seen that an Alternating Current generator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current. We have also studied the differences in single-phase, two-phase, and three-phase units. Both AC generators and motors have been discussed. In the chapter on motors we reviewed all of the common types of synchronous and induction motors as well as starting requirements of each type.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
