Distribution
System
Modeling
and
Analysis
The ELECTRIC POWER ENGINEERING Series
The ELECTRIC POWER ENGINEERING Series
series editor Leo Grigsy
series editor Leo Grigsby
Published Titles
Electromechanical Systems, Electric Machines,
and Applied Mechatronics
Sergey E. Lyshevski
Electrical Energy Systems
Mohamed E. El-Hawary
Electric Drives
Ion Boldea and Syed Nasar
Distribution System Modeling and Analysis
William H. Kersting
Linear Synchronous Motors:
Transportation and Automation Systems
Jacek Gieras and Jerry Piech
Forthcoming Titles
Induction Machine Handbook
Ion Boldea and Syed Nasar
Power System Operations
in a Restructured Business Environment
Fred I. Denny and David E. Dismukes
Power Quality
C. Sankaran
Distribution
System
Modeling
and
Analysis
William H. Kersting
New Mexico State University
Las Cruces, New Mexico
Boca Raton London New York Washington, D.C.
CRC Press
0812_frame_FM.fm Page iv Tuesday, July 31, 2001 10:49 AM
Library of Congress Cataloging-in-Publication Data
Kersting, William H.
Distribution system modeling and analysis / William H. Kersting
p. cm. -- (Electric power engineering series)
Includes bibliographical references and index.
ISBN 0-8493-0812-7 (alk. paper)
1. Electric power distribution–Mathematical models. I. Title. II. Series.
TK3001 .K423 2001
621.31—dc21
2001035681
CIP
This book contains information obtained from authentic and highly regarded sources. Reprinted material
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Visit the CRC Press Web site at www.crcpress.com
© 2002 by CRC Press LLC
No claim to original U.S. Government works
International Standard Book Number 0-8493-0812-7
Library of Congress Card Number 2001035681
Printed in the United States of America 1 2 3 4 5 6 7 8 9 0
Printed on acid-free paper
0812_frame_FM.fm Page v Tuesday, July 31, 2001 10:49 AM
Contents
1
2
........................................... 1
Introduction to Distribution Systems
1.1 The Distribution System......................................................................2
1.2 Distribution Substations ......................................................................2
1.3 Radial Feeders.......................................................................................5
1.4 Distribution Feeder Map.....................................................................6
1.5 Distribution Feeder Electrical Characteristics..................................8
1.6 Summary................................................................................................9
..................................................................... 11
The Nature of Loads
2.1 Definitions............................................................................................ 11
Individual Customer Load................................................................13
2.2
2.2.1 Demand ...................................................................................13
2.2.2 Maximum Demand................................................................13
2.2.3 Average Demand....................................................................14
2.2.4 Load Factor .............................................................................14
2.3 Distribution Transformer Loading...................................................15
2.3.1 Diversified Demand...............................................................16
2.3.2 Maximum Diversified Demand...........................................17
2.3.3 Load Duration Curve ............................................................17
2.3.4 Maximum Noncoincident Demand ....................................17
2.3.5 Diversity Factor ......................................................................18
2.3.6 Demand Factor .......................................................................19
2.3.7 Utilization Factor....................................................................19
2.3.8 Load Diversity ........................................................................20
2.4 Feeder Load.........................................................................................20
2.4.1 Load Allocation ......................................................................20
2.4.1.1 Application of Diversity Factors...........................21
2.4.1.2 Load Survey..............................................................21
2.4.1.3 Transformer Load Management............................25
2.4.1.4 Metered Feeder Maximum Demand ....................25
2.4.1.5 What Method to Use? .............................................27
2.4.2 Voltage-Drop Calculations Using Allocated Loads..........27
2.4.2.1 Application of Diversity Factors...........................27
2.4.2.2 Load Allocation Based upon
Transformer Ratings................................................31
2.5 Summary..............................................................................................32
Problems.......................................................................................... 33
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3
4
5
drop
rise
K
K
............................................. 39
Approximate Methods of Analysis
3.1 Voltage Drop........................................................................................39
3.2 Line Impedance...................................................................................41
3.3
“K” Factors ..........................................................................................43
Factor.......................................................................43
3.3.1 The
3.3.2 The
Factor........................................................................46
3.4 Uniformly Distributed Loads ...........................................................47
3.4.1 Voltage Drop ...........................................................................48
3.4.2 Power Loss ..............................................................................50
3.4.3 The Exact Lumped Load Model..........................................52
3.5 Lumping Loads in Geometric Configurations ..............................55
3.5.1 The Rectangle..........................................................................55
3.5.2 The Triangle ............................................................................60
3.5.3 The Trapezoid .........................................................................65
3.6 Summary..............................................................................................71
References .....................................................................................................71
Problems.......................................................................................... 71
......... 77
Series Impedance of Overhead and Underground Lines
4.1 Series Impedance of Overhead Lines..............................................77
4.1.1 Transposed Three-Phase Lines.............................................78
4.1.2 Untransposed Distribution Lines ........................................79
4.1.3 Carson’s Equations ................................................................81
4.1.4 Modified Carson’s Equations...............................................83
4.1.5 Primitive Impedance Matrix for Overhead Lines ............85
4.1.6 Phase Impedance Matrix for Overhead Lines ..................86
4.1.7
Sequence Impedances............................................................89
4.2 Series Impedance of Underground Lines.......................................95
4.2.1 Concentric Neutral Cable .....................................................96
4.2.2 Tape-Shielded Cables...........................................................101
4.3 Summary............................................................................................105
References ...................................................................................................105
Problems........................................................................................ 105
...... 109
Shunt Admittance of Overhead and Underground Lines
5.1 The General Voltage-Drop Equation ............................................. 110
5.2 Overhead Lines................................................................................. 111
5.3 Concentric Neutral Cable Underground Lines ........................... 115
5.4 Tape-Shielded Cable Underground Lines .................................... 119
5.5 Sequence Admittance.......................................................................121
5.6 Summary............................................................................................122
References ...................................................................................................122
Problems........................................................................................ 122
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6
7
8
............................................. 125
Distribution System Line Models
6.1 Exact Line Segment Model .............................................................125
6.2 The Modified Line Model ...............................................................132
6.3 The Approximate Line Segment Model .......................................136
6.4 Summary............................................................................................141
References ...................................................................................................141
Problems........................................................................................ 141
7.4.1
............................................................... 145
Regulation of Voltages
7.1 Standard Voltage Ratings ................................................................145
7.2 Two-Winding Transformer Theory................................................147
7.3 The Two-Winding Autotransformer..............................................152
7.3.1 Autotransformer Ratings ....................................................156
7.3.2 Per-Unit Impedance.............................................................158
7.4 Step-Voltage Regulators...................................................................162
Single-Phase Step-Voltage Regulators ..............................163
7.4.1.1 Type A Step-Voltage Regulator............................163
7.4.1.2 Type B Step-Voltage Regulator............................164
7.4.1.3 Generalized Constants ..........................................167
7.4.1.4 The Line Drop Compensator...............................168
7.4.2 Three-Phase Step-Voltage Regulators ...............................174
7.4.2.1 Wye-Connected Regulators..................................175
7.4.2.2 Closed Delta-Connected Regulators...................180
7.4.2.3 Open Delta-Connected Regulators .....................183
7.5 Summary............................................................................................193
References ...................................................................................................194
Problems........................................................................................ 194
............................................. 199
Three-Phase Transformer Models
Introduction.......................................................................................199
8.1
8.2 Generalized Matrices .......................................................................200
8.3 The Delta–Grounded Wye Step-Down Connection....................201
8.3.1 Voltages..................................................................................202
8.3.2 Currents .................................................................................206
8.4 The Ungrounded Wye–Delta Step-Down Connection...............212
8.5 The Grounded Wye–Grounded Wye Connection.......................222
8.6 The Delta–Delta Connection...........................................................224
8.7 The Open Wye–Open Delta Connection ......................................236
8.8 The Thevenin Equivalent Circuit...................................................242
8.9 Summary............................................................................................245
Problems........................................................................................ 245