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Transformer Application Fundamentals gives the reader a working knowledge of the important aspects of trans­formers, how they work, and how to apply them without getting deep into theory or mathematics. The simplified approach used is based upon “need to know” rather than knowledge for the sake of knowledge.

Completion of this course will be of little help in designing transformers, however it will be of great assistance in selling and applying transformers.

This text must be studied. All of the text should be read, the problems worked and the questions answered, if you are to receive full benefit. The course is designed to make learning enjoyable and as effortless as possible, but the reader must be prepared to work as well.

The points of importance are generally covered in the direct questions and the review questions. If you can choose the correct answers you probably have a good grasp of the important points. If you should find a particular point hard to understand, it is suggested that you also read the wrong answer response pages. These pages often carry additional information which will clear up the subject in question.

This has been written with the assumption that the reader is already well versed in basic electricity. If not, it is recommended that a basic electricity course be completed before proceeding.

A foundation for further study in the field of specialized transformer applications is provided.

Note to the Reader

Do not attempt to read this as you would an ordinary post. The pages are numbered consecutively, but they are not to be read this way. At the bottom of each page is an instruction indicating which page you are to read next. It may be forward or backward, so follow instructions carefully.

This text is “programmed” and makes use of branching programming (where you go to a different page for more information) and linear programming (where a question is asked and you will find the answer close by).

The course functions as a personal teacher. It gives you information and asks questions frequently. When you miss a question the correct answer is given, plus additional information which will assist you to under­ stand before proceeding to new material.

We suggest short sessions–one chapter at a session. This approach will be most productive. Take your time and study care­fully, being sure to follow instructions.

Synopsis of Contents

Here are brief descriptions and links to the chapters of the course.

For a full Table of Contents, see the right column.

The basics of transformer design and construction, and why they are necessary.

All about the central element powering transformers.

Windings, taps and connections.

Digging in deeper to the how and why of winding design.

Get into the weeds on the function, specific design elements, temperature rise and cooling.

Alternating voltage, generation and waves, values of the power.

Currents, capacities, impedance.

Power, power description, power factors and power correction.

Alternating voltage generation, phase connections, Wye and Delta systems.

Single phase on three phase circuits, three phase connections.

Connections, taps, unbalanced loads, single phase option.

Regulation, impedance, reactance, compensation.

Physical situation, testing, environmental corrections.

Help in calculations.

A glossary for reading the information.


  • Core Losses
  • Core Shapes
  • EI Cores
  • Magnetization and Flux
  • Built Up Cores
  • Cores – Other
  • Core Assembly and Sound
  • Treatment and Sound Magnetostriction
  • Review and Summary
  • Review Questions
  • Review Answers
  • Single Windings
  • Tap Changing
  • Tap Placement
  • Taps
  • Multiple Voltage
  • Multiple Windings
  • Series Connection
  • Parallel or Multiple Connections
  • Multiple Windings and Transformer
  • Taps and Transformer Size
  • Review and Summary
  • Review Questions
  • Review Answers
  • Additive and Subtractive Voltage
  • Termination Marking
  • Autotransformers
  • Copper Loss
  • Wire Size, Current and Current Density
  • Ratings for Multiple Voltages
  • Wire Size and Heating
  • Transformer Efficiency
  • Review and Summary
  • Tapped Secondary Windings
  • Reduced Capacity Secondary Taps
  • Full Capacity Secondary Taps
  • Special Secondary Taps
  • Review Questions
  • Review Answers
  • Functions of the Core.
  • Coupling Between Coils.
  • Treatment (Impregnation)
  • Temperature and Voltage Rating
  • Insulation Types
  • Hot Spot Temperature
  • Insulation Classes
  • Core and Coils
  • Insulation (Need for)
  • Impregnation Methods
  • Air Cooling
  • Standard Insulation Classes
  • Insulation Uses
  • Temperature Rise
  • Measuring Temperature Rise
  • Ambient Temperature
  • Transformer Cooling
  • Liquid Cooling
  • Review and Summary
  • Review Questions
  • Review Answers
  • Alternating Voltage Generation
  • Sine Wave Generation
  • Alternating Current
  • Effective Value or RMS
  • Instantaneous Values of Voltage and Current
  • AC Power
  • Review and Summary
  • Review Questions
  • Review Answers
  • Leading and Lagging Currents
  • Capacitive Reactance.
  • Inductance and Lagging Currents
  • Inductive Reactance
    Capacitance and Leading Currents
  • Impedance
  • Impedance-Current and Voltage Relationship
  • Impedance-Voltage Phasers
  • Power Factor
  • Review and Summary
  • Review Questions
  • Review Answers


Copyright Notice:

Transformer Application Fundamentals © 1970 – 2019, Jefferson Electric, Inc. No part may be reproduced in any form without written permission from the copyright holder.

This electronic file is to be used for promotional purposes only, to support the sale of Jefferson Electric products. No portion of this file may be used, in either electronic or in print form, for commercial purposes without the written permission of Jefferson Electric, 9650 South Franklin Drive, Franklin, WI 53132-8847. This file may be transmitted only in its entirety without any alterations to its content, appearance, or functionality.

Due to ongoing product development and technical enhancements, Jefferson Electric reserves the right to change technical specifications.