EMW Sensors & Mst__washington University

  • Published on
    30-Nov-2015

  • View
    10

  • Download
    2

Embed Size (px)

DESCRIPTION

research

Transcript

  • ELECTROMAGNETIC SENSORS FOR MEASUREMENTS ON

    ELECTRIC POWER TRANSMISSION LINES

    By

    ZHI LI

    A dissertation submitted in partial fulfillment of

    the requirements for the degree of

    DOCTOR OF PHILOSOPHY

    WASHINGTON STATE UNIVERSITY

    School of Electrical Engineering and Computer Science

    AUGUST 2011

  • ii

    To the Faculty of Washington State University:

    The members of the Committee appointed to examine the

    dissertation of ZHI LI find it satisfactory and recommend that it be accepted.

    ___________________________________

    Robert G. Olsen, Ph.D., Chair

    ___________________________________

    Patrick D. Pedrow, Ph.D.

    ___________________________________

    Mani V. Venkatasubramanian, Ph.D.

  • iii

    ACKNOWLEDGMENT

    I would like to thank my advisor Dr. Robert G. Olsen for his endless help during

    my stay in Pullman. He ignited my interest in the research on electromagnetics for

    power transmission lines. His patient and inspiring guidance always brought me back

    on the right track when I got lost in my research. Without his help and encourage, this

    dissertation would not have been possible. Also thanks to his mentoring of my life

    under the American culture background. I would like to thank my committee, Dr.

    Patrick D. Pedrow and Dr. Mani V. Venkatasubramanian for the helpful inputs for my

    research and career pursuits. Special thanks to, but not limit to, Dr. Anjan Bose, Dr.

    John B. Schneider, and Dr. Aleksandar D. Dimitrovski for help in my research and

    graduate curriculum.

    I would also like to thank my parents and my family for their continuous support

    and unconditional love, which have always been the source of my courage. Deepest

    appreciation also to my friends, whose support and encourage have helped shape this

    amazing journey in my life.

    Thanks to Xiaojing for holding my hand, with love.

  • iv

    ELECTROMAGNETIC SENSORS FOR MEASUREMENTS ON

    ELECTRIC POWER TRANSMISSION LINES

    Abstract

    by Zhi Li, Ph.D.

    Washington State University

    August 2011

    Chair: Robert G. Olsen

    The emergence of smart grid technology requires changes in the infrastructure of

    the electric power system. One of these changes is the addition of sensors to the

    transmission portion of the power system in order to determine useful information

    about the system such as line sag and direction of power flow. Unfortunately, there

    are a number of inhibitors to incorporating these additional sensors. These include

    issues of initial cost and/or maintenance. Therefore, what is needed (especially in

    sparsely inhabited areas) is new sensors that are inexpensive to manufacture, do not

    compromise safety, can be installed without taking transmission lines out of service

    and require low levels of maintenance.

    The focus of this dissertation is on electromagnetic (EM) field sensors, a novel

    type of sensor that can be used for monitoring the state of power lines. These sensors

    do not require contact with the power lines; rather they utilize electric and magnetic

    field coupling. Important states (such as voltage, current and phase sequence) and

    geometric parameters (e.g., line sag) of the power lines can be monitored based on

  • v

    inherent correlations between those variables and the electromagnetic fields produced

    by the power lines. While similar sensors have been available for many years, the

    unique feature of the sensors discussed here is that they utilize the relative phase of

    the EM fields in the vicinity of the line to provide significantly better sensitivity than

    has been previously available. In addition, they are inexpensive, easy to install with

    live working techniques and require only a low level of maintenance.

    Three types of sensors, point probes, and perpendicular and parallel distributed

    sensors will be studied using basic reciprocity theory and developed to the point of

    application. Several field experiments were conducted for validation. Finally,

    potential applications of the sensors for monitoring power lines are explored.

    LenovoHighlight

  • vi

    TABLE OF CONTENTS

    Page

    ACKNOWLEDGMENT .......................................................................................... III

    ABSTRACT ............................................................................................................... IV

    TABLE OF CONTENTS .......................................................................................... VI

    LIST OF FIGURES .................................................................................................. IX

    LIST OF TABLES .................................................................................................. XIII

    CHAPTER 1 INTRODUCTION .............................................................................. 1

    1.1 ELECTROMAGNETIC SENSORS FOR TRANSMISSION LINES ...................................... 4

    1.2 EM FIELDS DUE TO POWER TRANSMISSION LINES ................................................. 7

    CHAPTER 2 POINT PROBES .............................................................................. 15

    2.1 INTRODUCTION.................................................................................................... 15

    2.2 GENERAL THEORY OF POINT PROBES.................................................................... 17

    2.3 APPLICATIONS OF POINT PROBE ........................................................................... 23

    2.3.1 Power line voltage monitoring .................................................................... 23

    2.3.2 Sag monitoring ............................................................................................ 26

    2.3.3 Negative/Zero sequence voltage detection ................................................. 28

    2.4 LAB TESTS AND FIELD EXPERIMENTS OF POINT PROBE ........................................ 35

    2.4.1 Single-phase, single-probe lab test ............................................................ 35

  • vii

    2.4.2 Single-phase, two-probe lab test ................................................................ 37

    2.4.3 Field experiments ........................................................................................ 38

    CHAPTER 3 GENERAL THEORY OF LINEAR SENSORS ............................ 44

    3.1 APPROACH BY RECIPROCITY THEOREM ................................................................ 44

    3.1.1 Reciprocity theorem for general electromagnetic case ............................... 46

    3.1.2 Two situations for implementing reciprocity theorem ................................ 47

    3.1.3 Implementing reciprocity theorem .............................................................. 49

    3.1.4 Solutions to the horizontal sensor case ....................................................... 54

    3.2 APPROACH BY MODEL OF PER-UNIT-LENGTH VOLTAGE AND CURRENT SOURCES .. 56

    3.3 RELATIONSHIP BETWEEN THE TWO APPROACHES ................................................. 61

    CHAPTER 4 PERPENDICULAR LINEAR SENSORS ..................................... 66

    4.1 MODEL AND THEORIES........................................................................................ 67

    4.2 SAG MONITORING BY PERPENDICULAR LINEAR SENSOR ...................................... 75

    4.2.1 Power line models and parameters ............................................................ 75

    4.2.2 Effect of setting of Z1 and Z2 ...................................................................... 77

    4.2.3 Effect of sensor length ............................................................................... 80

    4.2.4 Effect of sensor height ............................................................................... 84

    4.2.5 Discussion on characteristic parameters of the sensor wire....................... 85

    4.3 NEGATIVE SEQUENCE MODE DETECTION BY PERPENDICULAR LINEAR SENSOR .... 88

    CHAPTER 5 PARALLEL LINEAR SENSORS ................................................... 97

    5.1 DIRECTIONAL COUPLER ....................................................................................... 98

  • viii

    5.2 FIELD EXPERIMENTS FOR DIRECTIONAL COUPLER.............................................. 106

    5.2.1 Objective and model ................................................................................. 106

    5.2.2 Settings and preparations of experiment ................................................... 109

    5.2.3 Results and analysis .................................................................................. 121

    CHAPTER 6 LOW FREQUENCY DIPOLE IN THREE-LAYER MEDIUM .. 133

    6.1 MODEL ............................................................................................................. 134

    6.2 FORMULATIONS BY SOMMERFELD INTEGRALS .................................................. 137

    6.3 UP-OVER-AND-DOWN INTERPRETATION OF THE FIELD PROPAGATIONS .............. 148

    6.3.1 Simplification of the integral of Iz1 and Iy1 ............................................... 151

    6.3.2 Approximations for E and H fields .......................................................... 162

    6.3.3 Up-over-and-down interpretation of wave propagation near interface ..... 164

    REFERENCES ......................................................................................................... 171

  • ix

    LIST OF FIGURES

    Fig. 1-1 Structure of a typical power system ................................................................ 2

    Fig. 1-2 An EM sensor made of styrofoam sphere covered by aluminum foils ........... 5

    Fig. 1-3 Patterns of electric and magnetic field flux of a power transmission line ...... 8

    Fig. 1-4 Fluorescent tubes lighted by EM field surrounding power lines .................... 9

    Fig. 1-5 Simplified model for transmission line above half-space of earth ................ 10

    Fig. 2-1 A general model of the point probe. .............................................................. 17

    Fig. 2-2 Two states of the point probe for applying the reciprocity theorem ............. 18

    Fig. 2-3 Thevenin equivalent circuit for the point probe model ................................. 21

    Fig. 2-4 Configuration of a 230kV, three phase, horizontal transmission line ........... 24

    Fig. 2-5 Space potential profiles for positive sequence voltage ................................. 24

    Fig. 2-6 Single probe placed under the three-phase power line .................................. 25

    Fig. 2-7 Applied voltage on the power line vs. induced current in point probe.......... 26

    Fig. 2-8 Line sag vs. induced current in point probe. ................................................. 27

    Fig. 2-9 Space potential profiles for negative sequence power line voltage .............. 29

    Fig. 2-10 Two probes designed to detect negative sequence component ................... 30

    Fig. 2-11 Design of a three-probe device used as a four-mode indicator ................... 32

    Fig. 2-12 Design of a negative-to-positive ratio measurement device ....................... 33

    Fig. 2-13 Single-phase, single-probe lab test .............................................................. 36

    Fig. 2-14 Space potential meter .................................................................................. 36

  • x

    Fig. 2-15 Single-phase, two-probe lab test ................................................................. 37

    Fig. 2-16 The site of the field experiment for point probe .......................................... 38

    Fig. 2-17 Positive sequence space potential profiles of the testing power line .......... 39

    Fig. 2-18 Settings for the field experiment ................................................................. 40

    Fig. 2-19 Probe currents of the field experiments....................................................... 42

    Fig. 2-20 Total current of the field experiments ......................................................... 42

    Fig. 3-1 A general model of the linear sensor ............................................................. 45

    Fig. 3-2 Special case for reciprocity theorem: sources reduces to line currents ......... 47

    Fig. 3-3 Two situations for implementing reciprocity theorem .................................. 48

    Fig. 3-4 Thevenins equivalent circuit for the linear sensor system ........................... 53

    Fig. 3-5 Model of the horizontal lossy wire sensor .................................................... 54

    Fig. 3-6 Model of a horizontal lossy linear sensor over perfect conductor ground .... 57

    Fig. 3-7 Replacing the external excitation with per-unit-length induced sources ...... 57

    Fig. 3-8 The sensor driven by only one set of the per-unit-length sources ................. 58

    Fig. 3-9 Equivalent circuit of the model driven by only one pair of sources ............. 59

    Fig. 4-1 Circuit loop of the perpendicular linear sensor and magnetic flux ............... 66

    Fig. 4-2 Model of a perpendicular linear sensor system. ............................................ 68

    Fig. 4-3 A perpendicular linear sensor reduces to point probe ................................... 73

    Fig. 4-4 Geometries of the perpendicular wire sensor ................................................ 75

    Fig. 4-5 Magnitude of the induced current on the sensor when Z1 = Z2 = 100 ........ 78

    Fig. 4-6 Phase angle of the induced current on the sensor when Z1 = Z2 = 100 ...... 79

    Fig. 4-7 Magnitude of the induced current when Z1 = 100 and Z2 = ................... 80

  • xi

    Fig. 4-8 Induced current at x = - L/2 vs. sensor length (Z1 = 100, Z2 = 100) ......... 81

    Fig. 4-9 Integration of space potential alone over the sensor wire. ............................ 82

    Fig. 4-10 Induced current at x = - L/2 vs. sensor length (Z1 = 100, Z2 = ) ............ 83

    Fig. 4-11 Sensor length vs. line sag for Model A (Z1 = 100 and Z2 = 100) ........... 85

    Fig. 4-12 Induced current at x = - L/2 vs. sensor length for different rw ..................... 86

    Fig. 4-13 Induced current at x = - L/2 vs. sensor length for different cw .................... 87

    Fig. 4-14 Using perpendicular linear sensors to detect negative sequence voltage .... 89

    Fig. 4-15 Magnitude of I1 and I2: (a) positive and (b) negative mode ........................ 90

    Fig. 4-16 Phase angle of I1 and I2: (a) positive and (b) negative mode ...................... 90

    Fig. 4-17 Design of perpendicular linear sensors to detect negative mode ................ 91

    Fig. 4-18 Magnitude of Itot for different modes after 30 phase shifting .................. 92

    Fig. 4-19 Move the two probes away from the center by 0.3m .................................. 93

    Fig. 4-20 Magnitude of total current when the probes are moved by 0.3 m ............... 94

    Fig. 4-21 Magnitude of total current for different modes of voltage in Model B ....... 95

    Fig. 5-1 Model of a horizontal parallel sensor...