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Overview & Energy Optimization of Power Distribution Transformers

A. Bhatia, B.E.

Course Outline

Distribution transformers functions to step-up & step-down voltage in transporting power economically from the power station to the final customer. Practical power transformers, although highly efficient, are not perfect devices. Transformer losses in power distribution networks can exceed 3% of the total electrical power generated and are estimated to total 140 billion kilowatt-hours (kWh) per year in the U.S.

This 4-hour course provides an overview of transformers and summarizes the key energy conservation measures pertaining to selection, application and operation of power transformers. The theoretical equations are kept minimum and the basic aspects are discussed wherever deemed fit.

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

Learning Objective

Upon completing the course, you will:

Intended Audience

This course is aimed at students, electrical & control engineers, energy auditors, O & M professionals, contractors, estimators, facility managers and general audience.

Course Introduction

Losses in electricity supply systems depend on the voltage level. These are minimized by transmitting electricity at as high a voltage as possible, consistent with demand load levels. Transformer is an electrical device that transfers AC energy from one circuit to another by magnetic coupling of the primary and secondary windings. This is accomplished through mutual inductance (M). To reduce the voltage to the desirable level, distribution transformers do consume a small portion of the electricity in a permanent manner. The resulting standby power losses account for up to 2% of the total electricity production.

In the past there was little concern for lowering losses in transformers. This was mainly due to the fact that when compared to motors and other electrical devices, transformers were considered to be very efficient. In recent years, however, there has been a growing concern for energy conservation and for the total operating costs of transformers. Furthermore, under the Department of Energy, as a requirement of the Energy Policy Act of 1992, studies are under way to determine if significant energy savings would merit setting loss goals for a wide range of transformers.

This course attempts to provide a basic overview of transformers with some emphasis on the transformer losses and energy conservation opportunities.

Course Content

The course content is in a PDF file Overview & Energy Optimization of Power Distribution Transformers. You need to open or download this document to study this course.

Course Summary

All transformers operate on the principal of magnetic induction where an AC voltage applied to the primary windings induces voltage in the secondary winding. Power transformers are very efficient, with losses of less than 0.5% in large units. Smaller units have efficiencies of 97% or above. It is estimated that on average transformer losses in power distribution networks can exceed 3% of the total electrical power generated.

The energy losses in electricity transformers fall into two components: no-load losses or iron losses (resulting from energizing the iron core; this phenomenon occurs 24 hours x 7 days, over the lifetime of the transformer, 30 years in average) and load losses (arising when providing power to a user, from the resistance of the coils when the transformer is in use, and for eddy currents due to stray flux). Transformers may lose 1 to 2% of energy transformed as heat when they are lightly loaded.

Technical solutions exist to reduce transformer losses by 75% at minimum (when replacing with modern transformers) or even by 90% (when replacing transformers over 30 years old). Energy-efficiency can be improved with better transformer design i.e. selecting better, lower-core-loss steels; reducing flux density in a specific core by increasing the core size; increasing conductor cross-section to reduce current density; good balancing between the relative quantities of iron and copper in the core and coils; amorphous iron transformers and so on...

Most distribution and general purpose transformers are currently purchased on a first cost basis without regard for losses or the total cost of ownership. Distribution transformers present a range of energy efficiency. Promoting the most energy efficient transformer technology, when replacing old equipment, can generate significant amount of energy savings on attractive paybacks.


Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

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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.