# AC/DC Motor Theory

ITC Learning’s AC/DC Motor Theory library was specifically developed for electricians and electronic technicians as well as for the multi-craft training needs of process and manufacturing facilities. This library consists of 11 interactive, on-line lessons that address AC and DC motor theory. These lessons take approximately 30 to 45 minutes to complete.

### Introduction to AC Components and Motors

Description: This is the first lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson identifies the components of an AC motor and explains their functions. Basic magnetic principles, sine waves, methods of increasing magnetic flux in a conductor, and how a rotating field is created in an AC Motor are presented.

Prerequisites: None

Topics:

Introduction to AC Components

Magnetic Principles

The Sine Wave

Flux Field

Increasing Magnetic Flux

Objectives:

• Identify the components of an AC Motor and explain their function
• Explain the basic principles of magnetism
• Interpret the characteristics of a current as represented on a sine wave
• Describe the effect of AC current on a conductor
• Describe the methods of increasing magnetic flux in a conductor
• Explain how a rotating field is created in an AC Motor

Description: The second lesson in the iKNOW™ AC/DC Motor Theory Library, this lesson explains synchronous speed and how to calculate it. The lesson demonstrates the relationship between phased current and rotor spin and induction and its effect on a rotor. Slip and how to calculate slip using its formula are also covered.

Prerequisites: Review of the lesson, Introduction to AC Components and Motors, or knowledge of AC motor components and magnetic principles is recommended.

Topics:

Current and Rotating Field

Synchronous Speed

Rotor Movement

Rotor Spin

Slip

Objectives:

• Explain and be able to calculate synchronous speed
• Explain induction and its effect on a rotor
• Explain the relationship between phased current and rotor spin
• Explain slip and know its formula

### Three-Phase Motors – Part 1

Description: This is the third lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson defines and explains the components and functions of various three-phase motors. The lesson also defines torque and explains its role in motor operation.

Prerequisites: None

Topics:

Squirrel Case Motors

Wound Rotors

Induction Characteristics

Reluctance Synchronous

Objectives:

• Describe the design of a squirrel cage rotor
• Explain the function of a squirrel cage rotor’s components
• Describe the design of a wound rotor
• Explain the function of a wound rotor’s components
• Define torque and explain its role in motor operation
• Explain the design of a reluctance motor and how it works

### Three-Phase Motors – Part 2

Description: This is the fourth lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson defines and explains the components and functions of externally excited motors, starters, and variable speed drives. There is also a review topic to reinforce the information covered in the lesson, Three-Phase Motors – Part 1.

Prerequisites: Completion of the lesson, Three-Phase Motors – Part 1, is recommended.

Topics:

Externally Excited Motors

Starters

Variable Speed Drives

Three-Phase Review

Objectives:

• Explain the design of an externally excited motor
• Explain how an externally excited motor works
• Explain the function of a motor starter
• Describe the most common types of motor starters
• Describe a variable speed drive and its effect on voltage and frequency

### Single-Phase Motors

Description: This is the fifth lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson trains the participants to distinguish single-phase motors from three-phase motors. Split-phase motors and capacitance start motors are discussed.

Prerequisites: Completion of the lessons, Three-Phase Motors – Part 1 and Part 2, is recommended.

Topics:

Single-Phase Motors

Split-Phase Motors

Capacitor Start Motors

Summary

Objectives:

• Distinguish a single-phase motor from a three-phase motor
• Explain the design of a split-phase motor and how it works
• Explain the design of a capacitance start motor and how it works

### Introduction to DC Motors

Description: This is the sixth lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson introduces the learner to DC Motors and their basic components.

Prerequisites: None

Topics:

History of DC Motors

Basic Components

Armature Components

Brushes

Objectives:

• Identify the general characteristics of a DC motor
• Identify the advantages of a DC motor
• Identify the basic components of a DC motor
• Explain the function of DC motor components
• Identify the components of the armature and explain their function
• Identify the components of the brush assembly and explain their function

### Introduction to DC Motor Theory

Description: This is the seventh lesson in the iKNOW™ AC/DC Motor Theory Library. The lesson introduces participants to DC motor theory.

Prerequisites: Knowledge of DC motor components and magnetic principles or review of the lessons, Introduction to AC Components and Motors and Introduction to DC Motors, is recommended.

Topics:

Flux Interaction

Commutation

Multiple Windings

Objectives:

• Explain the effect of armature current on the main flux field and how it results in motor action.
• Explain the process of commutation and how it maintains direct current in a DC motor.
• Describe how the number of windings and commutator segments effects torque and mechanical power of a DC motor.

### Armature Reaction, Compensation, and Induced Voltage

Description: The eighth lesson in the iKNOW™ AC/DC Motor Theory Library, this lesson demonstrates armature reaction, compensation, and induced voltage.

Prerequisites: Knowledge of DC motor components and review of the lesson, Introduction to DC Motor Theory, is recommended.

Topics:

Armature Reaction

Compensation

Induced Voltage

Objectives:

• Explain how armature reaction shifts the neutral plane in a DC motor
• Explain how armature reaction affects motor operation
• Explain what measures will correct armature reaction
• List the requirements for induced voltage in a motor
• Explain counter-EMF.

### Series, Shunt, and Compound DC Motors

Description: This is the ninth lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson instructs the participant in the design of series wound, shunt wound, and compound DC motors and how they work.

Prerequisites: Knowledge of DC motor components and review of the lessons, Introduction to DC Motor Theory and Armature Reaction, Compensation, and Induced Voltage, is recommended.

Topics:

Series Wound Motors

Shunt Wound Motors

Compound Motors

Objectives:

• Explain the design of a series wound DC motor
• Explain how a series wound DC motor works
• Explain the design of a shunt wound DC motor
• Explain how a shunt wound DC motor works
• Explain the design of a compound wound DC motor
• Explain how a compound wound DC motor works

### Permanent Magnet, Universal, and Brushless DC Motors

Description: This is the tenth lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson instructs the student in the design of permanent magnet, universal, and brushless DC motors and how they work.

Prerequisites: Knowledge of DC motor components and review of the lessons, Introduction to DC Motor Theory and Series, Shunt, and Compound DC Motors, are recommended.

Topics:

Permanent Magnet Motors

Universal Motors

Brushless Motors

Objectives:

• Explain the design of a permanent magnet DC motor
• Explain how a permanent magnet DC motor works
• Explain how a universal motor runs off of DC power
• Explain the design of a brushless DC motor
• Explain how a brushless DC motor works

### DC Motor Controls

Description: This is the final lesson in the iKNOW™ AC/DC Motor Theory Library. This lesson trains participants in starters, rotation direction, speed control, and drive controls of DC motors.

Prerequisites: Knowledge of schematics is recommended as well as review of the lessons, Introduction to DC Motor Theory and Series, Shunt, and Compound DC Motors.

Topics:

Starting DC Motors

Reverse Direction

Speed Control

DC Drives

Objectives:

• Explain why a reduced voltage starter is sometimes needed in a motor
• Explain how a reduced voltage starter works
• Explain what determines the direction of rotation of a DC motor
• Explain how a reverse contactor works
• Explain how to control the speed of a DC motor
• Explain how a tapped resistor works
• Explain how a field rheostat works
• Explain a DC drive’s control system
• Explain how a DC drive control system works