Power System Distribution

Power System Distribution

(Parte 1 de 4)

Power Transmission and Distribution

2nd Edition

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Power

Transmission and Distribution

2nd Edition

Anthony J. Pansini, E.E., P.E.

Pansini, Anthony J.

Power transmission and distribution/Anthony J. Pansini.--2nd ed. p. cm.

Includes index. ISBN: 0-88173-503-5 (print) — 0-88173-504-3 (electronic) 1. Electric power transmission. 2. Electric power distribution. I. Title.

TK3001.P29 2005 621.319--dc22 2004056439

Power transmission and distribution, second edition/Anthony J. Pansini ©2005 by The Fairmont Press, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electr mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher

Published by The Fairmont Press, Inc. 700 Indian Trail Lilburn, GA 30047 tel: 770-925-9388; fax: 770-381-9865 http://www.fairmontpress.com

Distributed by Marcel Dekker/CRC Press

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Printed in the United States of America 10 9 8 7 6 5 4 3 2 1

0-88173-503-5 (The Fairmont Press, Inc.) 0-8493-5034-4 (Dekker/CRC Press)

While every effort is made to provide dependable information, the publisher authors, and editors cannot be held responsible for any errors or omissions.

In memory of my parents in appreciation of their sacrifices and encouragement

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Preface to the Original Edition—1990
Preface to the Second Edition—2004

vii

1 Introduction, Consumer Characteristics
2 Distribution System Electrical Design
3 Subtransmission System Electrical Design
4 Transmission System Electrical Design
5 Electrical Pr otection
6 Direct Current Transmission
7 Overhead Mechanical Design and Construction
9 Associated Operations

Chapter 8 Underground Mechanical Design and Construction

A Circuit Analysis
B Symmetrical Components
C Review of Complex Numbers

Appendix

Delivery Systems Ef ficiencies
E Street Lighting—Constant Curr ent Circuitry
F Economic Studies
HUnited States and Metric Relationships

DTransmission and Distribution GThe Grid Coordinate System, Tying Maps to Computers Index ................................................................................................................

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It has been some time since a book was written on power transmission and distribution, a book that can be used as a textbook for the many for whom this subject, for one reason or another interest. In one place, there can be found the electrical, mechanical and economic considerations associated with the successful planning, design, construction, maintenance and operation of such electrical systems.

Simple explanations of materials and equipment describe their roles in the delivery of power, in small and large quantities, to homes and offices, farms and factories. They meet the needs of nontechnical people, including the legal and financial sectors, as well as those whose interests may involve the promotion of equipment sales and maintenance, public information, governmental and other functions and activities. For the neophyte engineer and the seasoned operator the practical technical discussion provides reference and r bases and tools employed in meeting the problems that arise in their daily endeavors. And, finally, the student and researcher will find sufficient theory and mathematical analyses to satisfy their thirst for knowledge and to impress their neighbors with the depth of their intellect!

Both the young who enjoy the benefits of modern electrical supply and the older groups who have seen and experienced the r able development made in its transmission and distribution must recognize that such advances are the work of many to whom a debt is due. And to some of us who have been given the privilege of making even slight contributions, we are grateful for the opportunities afforded us during a most enjoyable and fulfilling career.

Thanks are extended to the people who have been helpful along the way, too many to name individually, and to the staf mont Press who have aided in the preparation and publishing of this work. The contributions of material and illustrations by the manufacturers for which I am extremely grateful, are especially acknowledged. In any work, errors somehow manage to intrude, and for any ing through the many years in which I have been engaged in this and kindred endeavors.

Anthony J. Pansini

Some twenty years have passed since the original publication of this book, normally sufficient to warrant an updating dictated by events and heralding the arrival of a new century. The explosion of electr cally operated devices (computers, robots, automatic contr required micro refinements in the quality of electric supply that could not tolerate those associated with the macro commercial supply of this commodity; necessary corrective actions peculiar to each such application were (and are) undertaken by the individual consumer. But the continually increasing dependence on electricity in practically every one of life’s endeavors also called for improvements in the quality standar supply to which this updating is addressed.

Notable events during this twenty-year period that helped in calling for better quality standards for those elements associated with r ability include the deregulation of electric (and other) utilities, the events of September 1, 2001, and the blackouts on northeast North August 14, 2004, in the London area and Italian peninsula within two weeks of each other. And on the positive side, the proliferation of automation brought about by the blooming electronic technology

Transmission systems have been the subject of the gr

Under deregulation, their role in the supply chain has been essentially reversed, from being the back up and peak supplier in generation-based systems, they become the main source of supply with generation r duced to a minimum if not entirely eliminated (to reduce capitalization and its effect on rate structures in a competitive market) Figur economic and environmental reasons, transmission lines ar areas of sparse population making them subject to the vagaries of man and nature, tailor made for assaults by vandals and saboteurs. Finally with transmission lines connected together in a grid, supposedly for better reliability and economy, failures causing the outage of a line may cause another of the lines to trip open from overload, causing another and another line to “cascade” open until total area blackout occurs.

It appears, quite unexpectedly, that the application of loop cir substantially improves the reliability of such transmission lines. Loop

xii

Figure P-1. Simplified schematic diagram of transition from regulated to deregulated supply systems.

xiii for those situated on the section on which the fault occurs) and especially if both halves of the loop circuit are not mounted on the same supporting structures. The reliability of the deregulated line is enhanced, and similarly, the damage inflicted by a saboteur or vandal may be limited to a section of the line. In the case of the transmission grid, supplanting it with a number of loop circuits not only r possibility of lines cascading open from overloads or instability permits the circuits to be loaded nearer their full capacity

Distribution systems have also been affected by these events, although not in the same manner of vulnerability as transmission systems. Where additional generation, and/or transmission was not available, or too great an expenditure to supply some additional distribution loads, distributed generation made its entry on the scene. Here small generating units, usually powered by small gas turbines, are connected dir to the distribution system, in the same manner as larger cogeneration units. These units may be both consumer- or utility-owned and oper ated, and may constitute safety hazards.

The chapter on street lighting is relegated to the appendices not only as essentially obsolete, but as an example of constant curr cuitry. In its stead is a description of direct-current transmission line with its positive and negative features, but an excellent futur the electric supply scenario.

A Texas size thank you goes out to all who have dir rectly contributed in the publishing of this work and especially to The Fairmont Press for their help and support.

Introduction, Consumer Characteristics

The system of delivery of electricity to consumers parallels that of most other commodities. From the generating or manufacturing plant, this product is usually delivered in wholesale quantities or via transmission facilities to transmission substations that may be compar gional warehouses. From there, the products may (or may not necessarily) be further shipped to jobbers over subtransmission lines to distribution substations or local depots. The final journey delivers these products to retailers via distribution systems that supply individual consumers. One important difference in this comparison is the lack of storage capability (for practical purposes) of electricity; every unit of electricity consumed at any moment must be generated at that same moment. A diagram of an electric utility system indicating the division of operations is shown in Figure 1-1. This work concerns the transmission and distribution elements.

Just as many of the larger manufacturing companies began as small enterprises, so, too, did many of the electric utilities. The first commercial electric system was constructed and placed in operation in 1882 by Thomas Alva Edison in New York City. It was a dir system that served a limited number of consumers in the vicinity of the plant at a nominal voltage of 100 volts. A number of other small systems (also direct current) in urban and suburban areas were supplied fr generating facilities of manufacturing factories. From these maverick systems that, in some instances, grew like Topsy without planning, the large utility systems were to be formed. Interestingly, almost a century later, privately owned generating facilities of industrial and commer companies were once again to exercise that same function. The sale of their excess energy through electrical connections to utility companies’

The invention of the transformer in 1883 in England by John Gibbs and Lucien Gaullard, together with the invention of the alternating cur rent induction motor and the development of polyphase cir

Figure 1-1. Electric System Divisions—Note Overlap (Courtesy Westinghouse Electric Co.) sion and distribution systems. Transmission of electric power dates fr 1886 when a line was built at Cerchi, near the city of Turin in Italy transmit some 100 kilowatts 30 kilometers, employing transformers, to raise and lower a 100 volt source to 2000 volts and back to 100 volts for utilization. In the same year, the first alternating current distribution system in the United States, also using transformers, was put into operation at Great Barrington in Massachusetts: the 100 volt system included two 50 light and four 25 light transformers serving 13 stor doctors’ offices, a barber shop, telephone exchange and post of a 500 volt source.

The adoption of alternating current, employing transformers, together with the general public’s acceptance of the less than pleasing overhead facilities almost entirely accounts for the unparalleled expansion experienced by the electric industry. The successful combination of transformer and overhead installations exemplifies a basic solution of the electrical, mechanical and economic problems associated with the design of transmission and distribution systems, as well as their construction, maintenance and operation. These three problems, although subject to independent solutions, interact upon each other

Electrical design considerations are based generally on acceptable values of loss in electrical pressure or voltage drop and those of ener loss. These considerations may be modified to accommodate desir protection, environmental and other requirements. The permissible values determine the size of conductors and the associated insulation r quirements. The physical characteristics of the conductors impact on the mechanical designs of such systems.

Mechanical design involves the study of structures and equipment.

It includes the selection of proper materials and their combination into structures and systems in such a manner as to meet the electrical design requirements, giving due consideration to matters of str temperature variations, length of life, appearance, maintenance, and other related factors.

Economic design includes the investigation of relative costs of two or more possible solutions to the combined electrical and mechanical requirements. The choice is governed (although not necessarily) not by the lowest annual carrying charge on the investment in the systems studied, but by that which is equal (or closest) to the annual cost of applicable conditions. These factors pertain generally to safety and environmental requirements as well as provision for possible futur mands for electric power, creating changes that may affect the several components involved in the solution to design problems; for example, new technology, revised codes and standards, inflation, new r and environmental requirements, etc. The final decision must also satisfy the electrical and mechanical design requirements. These criteria apply to both the transmission and distribution systems.

Referring to the diagram in Figure 1-1, although it has been customary to consider generation, transmission and distribution as thr interdependent elements constituting a single enterprise, as one electric utility system, financial and conservation considerations have given rise to consideration of each of the three as separate and distinct enterprises. Acquisition of each of the three by independent parties could be a means of diversifying their investments. Problems of cooperation in the operation of such separately owned systems would affect the consumer could possibly cause the construction of duplicate competitive systems.

In the presentation of the material that follows, it will be assumed that the reader is familiar with the essentials of electricity, including vector representation, concerning the properties of both direct and alternating current circuits, including resistance, inductance, capacitance, impedance, and their Ohm’s Law relationships.

Although the usual flow of electricity to the consumer is fr generating plant through the transmission system into the distribution system, the discussion will treat the delivery system in the r starting with the consumer and working toward the central generating plant.

To begin the electrical design of transmission and distribution systems, it is necessary to know the characteristics of the building blocks upon which the design of the systems is predicated; that is, the consumer to be served. Obviously, each consumer cannot be consider independently, but they may be studied as a class and as gr affect the final design of the systems.

determined include:

1.The total consumption of electricity over a period of time, (say) annually.

2.The changes in rate of consumption, (say) hourly, over periods of time: daily, weekly, monthly, annually.

3.The voltage required for the proper operation of the loads to be served; the tolerance permitted in the variation of this voltage, and whether the rapidity of such variations would cause flicker of lights to result.

(Parte 1 de 4)

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