Print this page Understanding Three-Phase Transformers
Ralph Fehr, Ph.D., P.E.
Course Outline
Transformer Fundamentals
The Ideal Transformer
Transformer Circuit Model
The Per-Unit Method of Calculation
Transformer Impedance
Common Three-Phase Connections
The Delta Connection
The Wye Connection
The Delta-Wye Transformer
This course includes a multiple-choice quiz at the end, which is designed to
enhance the understanding of the course materials.
At the conclusion of this course, the student will:
- Understand the importance of transformers in a power system;
- Know the basic construction of a power transformer;
- Be able to construct a transformer circuit model and explain what each element in the model represents;
- Understand why the per-unit system is useful for power system calculations involving transformers;
- Be able to perform basic power system calculations using the per-unit system;
- Be able to convert per-unit impedances from one set of bases to another;
- Know how transformer impedance is measured, and what percent impedance represents;
- Understand how transformer impedance influences voltage drop and short circuit current;
- Understand the advantages and disadvantages of the delta connection;
- Understand the advantages and disadvantages of the wye connection;
- Be able to analyze a delta-wye transformer using per-unit currents, showing how magnitude changes and phase shifts come about; and
- Be able to apply the per-unit current analysis method to more complicated transformer connections than the delta-wye.
This course is designed for utility, plant, or consulting engineers and technicians involved in the selection, specification, application, operation, maintenance, installation, or engineering of the installation of three-phase transformers. If you have recently begun a career or assignment in these areas, this course will be of value to you.
Benefit to Attendees
Students completing this course will gain intuitive insight as to how three-phase transformers work. A careful balance between theory and practical application has been struck to allow students completing this course to use the knowledge gained from the course on the job. The general techniques of per-unit calculation and per-unit current analysis can be applied generally to solve many types of practical problems.
Course
Introduction
Three-phase power systems have been used for the past century to provide electrical power throughout the world. A key component of the power system is the transformer, without which we would not have the ability to efficiently change voltage levels. Three-phase transformers do not need to be complicated or confusing. This course shows a logical and methodical means to understand the three-phase transformer, including an analytical method that can be applied to understand any transformer connection. The per-unit system, which is indispensible when dealing with transformers, is also presented in a clear and concise way.
Course Content
In this lesson, you are required to study the following document:
Understanding Three-Phase Transformers
Please click on the above underlined hypertext to view, download or print the document for your study. Because of the large file size, we recommend that you first save the file to your computer by right clicking the mouse and choosing "Save Target As ...", and then open the file in Adobe Acrobat Reader. If you still experience any difficulty in downloading or opening this file, you may need to close some applications or reboot your computer to free up some memory.
Course Summary
This course provides a review of basic transformer theory, including both the ideal model and a lumped parameter model which accounts for winding and core losses. The per-unit system of calculation is covered to provide a simplified means of dealing with the transformer turns ratio. The concept of transformer impedance is explored, including a method to measure impedance. Then, the common three-phase connections (delta and wye) are studied, including a discussion of the advantages and disadvantages of each. The course culminated with a thorough examination of the most common three-phase transformer connection – the delta-wye, using an analysis method that can be applied to any transformer connection.
References
For additional technical information related to this subject, please refer to:
Industrial Power Distribution – 2nd Edition, Ralph Fehr, Wiley / IEEE Press, 2014.
Information at: http://www.ralphfehr.com
http://www.allaboutcircuits.com/vol_2/chpt_10/6.html
http://ecmweb.com/content/using-single-phase-transformers-create-3-phase-systems
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.
