Electrical Fundamentals – Introduction to Inductance

A. Bhatia, B.E.

Course Outline

Inductance is an effect which results from the magnetic field that forms around a current-carrying conductor. Electric current through the conductor creates a magnetic flux proportional to the current. A change in this current creates a change in magnetic flux that, in turn, generates an electromotive force (emf) that acts to oppose this change in current. Inductance is a measure of the generated emf for a unit change in current.

This 3-hr course material provides insight to the basic concepts of inductance and is based entirely on Naval Education and Training Materials (NAVEDTRA 14173), Electricity and Electronic Training Series; Module-2, Chapter 2 titled “Inductance”.

The course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of course materials.

Learning Objective

At the conclusion of this course, the student will be able to:

• Define inductance and state the meanings of the terms induced emf and counter emf;
• State Lenz's law;
• Describe the effect of inductance in steady direct current and the direct current that is changing in magnitude;
• List five factors that affect the inductance of a coil and state how various physical changes in these factors affect inductance;
• Describe the transient response of an RL circuit;
• State the three types of power loss in an inductor;
• Define the term "mutual inductance” and “coefficient of coupling”;
• Solve for mutual inductance, given the inductance values of and the coefficient of coupling between two series-connected inductors; and
• Write the formula for the "total inductance" of two inductors connected in series-opposing.

Intended Audience

This course is aimed at students, professional engineers, service technicians, energy auditors, operational & maintenance personnel, facility engineers and general audience.

Course Introduction

An inductor is a passive electronic component that stores energy in the form of a magnetic field.

In its simplest form, an inductor consists of a wire loop or coil. The inductance is directly proportional to the number of turns in the coil. Inductance also depends on the radius of the coil and on the type of material around which the coil is wound. For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high permeability. Variations include coils wound on various core materials, the most popular being iron (or iron alloys, laminations, or powder) and ferrite, a black, nonconductive, brittle magnetic material.

Inductance is designated by letter “L” and the symbol for an inductor looks like a coil of wire; that's because, in its simplest form, that's all it is. Examples of inductors or devices having inductance are transformers, chokes, coils relays and motors. Inductors find heavy use in radio frequency (RF) circuits, serving as RF "chokes" and as parts of tuned circuits.

Course Content

In this course, you are required to study Naval Education and Training Materials (NAVEDTRA 14173), Electricity and Electronic Training Series; Module-2, Chapter 2 titled “Inductance”:

Inductance (Chapter 2, NAVEDTRA 14173)

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Course Summary

Inductance in any circuit is the property that opposes any change in the existing current.

When an alternating voltage is applied to an inductance, a back electromotive force (emf) is generated in the inductance. This emf is proportional to the rate at which the current changes -- The more rapid the change, the greater the back emf developed. And this, in turn, is proportional to the frequency of the alternating voltage.

Inductance can be simply understood by thinking about the magnetic field lines around a current flowing through a conductor. When a current flows in any conductor, like a simple wire, there will be circular rings of magnetic field lines around the wire that act as though they endlessly spin around and around the conductor. The Right-Hand Rule describes the direction in which the rings circulate. Point the thumb of your right hand in the direction of the current and your fingers curl in the direction the rings circulate.

While the energy in the field is about the total number of rings of magnetic field lines around the conductor, inductance is not about the absolute number of rings. If we double the current, we double the number of rings of magnetic field lines but we don’t change the inductance of the wire. Rather, inductance is a measure of the efficiency of the conductor to create rings of magnetic field lines, at the price of the current through the conductor. In general inductance depends on:

• The core material - The better the core conducts magnetic flux lines (higher permeability), the higher the inductance.
• The number of turns - More turns gives higher inductance.
• Cross-sectional area - A larger area gives higher inductance.
• Length - Longer length gives smaller inductance.

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.