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ELECTRICAL ENGINEERING – Vol. III - Direct Current Machines - Edward Spooner

DIRECT CURRENT MACHINES
Edward Spooner
The University Of New South Wales, Australia.
Keywords: Electric machines, dc motor, electromagnetic induction, Faraday's Law, commutator.
Contents

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1. Introduction
2. Magnetism and Electromagnetic principles
2.1. Permanent Magnets
2.2. Magnetic Field around Conductors
2.3. Magnetic Field around a Coil
2.4. Electromagnets
2.5. Magnetic Strength of Electromagnets
2.6. Electromagnetic Induction
3. Current Carrying Wires and Coils
3.1. Force on a Wire in a Magnetic Field
3.2. Force and Torque on a Coil in a Magnetic Field
4. Basic Motor Principles
4.1. The Commutator and Motor Action
4.2. Simplified Version of the dc Motor
4.3. Sizes of Machines (related to Torque)
4.4. Construction of Motors
4.5. The Stator of a dc Machine
4.6. Rotor
4.7. The Commutator
4.8. Electromotive Force (EMF) in dc Machines
5. Machine equations and circuits
5.1. Basic Equivalent Circuit of a dc Motor.
5.2. Direct current Motor Operation & Torque generation
5.3 DC Machine Torque Equations
5.4. DC Machine Equations and Speed Regulation
5.5. Machine Power and Losses
6. Types of dc Machine
6.1. Permanent Magnet
6.2 Shunt Wound
6.3 Separately Excited
6.4. Series Connected
6.5. Compound Connected Motor
7. Stepper Motors
7.1. General
7.2. Permanent Magnet Stepper Motors
7.3. Reluctance Stepper Motors
7.4. Torque – Step Rate
8. Conclusions

©Encyclopedia of Life Support Systems (EOLSS)

ELECTRICAL ENGINEERING – Vol. III - Direct Current Machines - Edward Spooner

Glossary
Bibliography
Biographical Sketch
Summary
This chapter gives a background to the principles behind the operation of dc motors and stepper motors. Permanent magnet, shunt, separately excited, series and compound wound dc motor connections are described. A description of the equations behind the basic behavior of these machines is given and the torque vs speed and speed vs armature (voltage and current) characteristics are illustrated, which gives a background to the control of these motors.

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1. Introduction
Electrical machinery has been in existence for many years. The applications of electrical machines have expanded rapidly since their first use many years ago. At the present time, applications continue to increase at a rapid rate.

The use of electrical motors has increased for home appliances and industrial and commercial applications for driving machines and sophisticated equipment. Many machines and automated industrial equipment require precise control. Direct current motors are ideal for applications where speed and torque control are required. Direct current motor design and complexity has changed from early times where dc machines were used primarily for traction applications. Direct current motors are used for various applications ranging from steel rolling mills to tiny robotic systems. Motor control methods have now become more critical to the efficient and effective operation of machines and equipment. Such innovations as servo control systems and industrial robots have led to new developments in motor design.

Our complex system of transportation has also had an impact on the use of electrical machines. Automobiles and other means of ground transportation use electrical motors for starting and generators for their battery-charging systems. Recently there have been considerable developments in electric vehicles and also in hybrid electric vehicles which use a combination of a dc motor and an internal combustion engine for efficient operation.

In this chapter machines driven by dc electrical supplies are considered. Since the operation of this type of machine is based upon the flow of current in conductors and their interaction with magnetic fields, common principles that underlie the behavior of...
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