Overcurrent Protection for Electric Utility Systems - a PDH Online Course for Engineers, Architects and Surveyors

Overcurrent Protection for Electric Utility Systems

Course Outline

The course begins with a discussion of sectionalizing philosophy including the types of faults that frequently occur, zones of protection, and some of the issues to consider when designing a protective scheme. Fault current calculations are briefly covered and then each of the common protective devices used on a distribution system are discussed. Application issues with each type of protective device are also reviewed. The course ends with a comprehensive example of how to protect a typical distribution circuit.

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

Learning Objective

After taking this course you should,

Understand the coordination philosophies that enhance reliability;
Know the types of faults that occur on distributions systems;
Be able to explain zones of protection;
Be able to explain the concept of “fuse saving”;
Understand what is needed to develop a sectionalizing study;
Know the four possible fault types;
Know how to calculate fault currents;
Know how to calculate per-unit values;
Know how to calculate a distribution voltage transformation;
Be able to calculate the impedance of a autotransformer;
Understand the fault currents on the supply side of a transformer;
Be able to explain the benefits of a circuit breaker;
Understand how oil circuit reclosers operate;
Be able to explain the benefits of an automatic sectionalizer;
Know the benefits and drawbacks of using fused cutouts;
Know how to apply different types of sectionalizing equipment;
Be able to explain what is meant by the term “cold load pickup”; and
Understand how layout a simple protective scheme for a distribution system.

Intended Audience

This course is intended for electrical engineers and others who want to understand how electric power system overcurrent protective schemes are designed and applied.

Benefit to Attendees

This course is a brief overview of a complex subject. It gives a conceptual review of how the calculations are made and protective schemes are designed, and should help you to understand the basics of designing a protective scheme.

Course Introduction

This course is an overview of how sectionalizing and protection studies are performed on electric distribution systems. It is not intended to provide a complete and exhaustive discussion of the subject, but rather to present the reader with helpful information and examples that will typically be encountered.

Within the arena of sectionalizing, there are many aspects of the subject that are established, quantifiable, and part of national standards. Included in this body of information are specific time-current characteristics of fuses and relays, the methods of calculations for available short-circuit current, and the standard damage points for distribution transformers. There are also many aspects of sectionalizing that are more subjective, debatable, and influenced by experience. These include “fuse save” versus “fuse blow,” coordination margins, and transformer protection practices. This reflects the idea that system protection is partly science and partly art.

This course concentrates on the “science” side of the subject and offers some well established practices and conventions on the “art” side. In the end, it is the responsibility of a utility’s protection engineer to recognize the specific needs and goals of the utility and apply the principles herein to the available equipment and technology to accomplish the best combination of reliability and economics possible.

Course Content

This course content is in the following PDF document:

Overcurrent Protection for Electric Utility Systems

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Course Summary

In this course we have reviewed sectionalizing philosophy, fault current calculations, discussed common protective devices and how to apply different types of protective devices. The course was summarized with a comprehensive example of how to protect a typical distribution circuit.

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.