By: MOHD AZIZ ARIS ERMEEY ABD KADIR PROF. DR ZAIKIAWANG PROF. MADYA AHMAD ISMAIL MAY UiTM

Transcription

1 NONDESTRUCTIVE AND NONCONTACT DIELECTRIC MEASUREMENT METHODS FOR TRANSFORMER OIL USING FREE SPACE MICROWAVE MEASUREMENT SYSTEM IN GHZ FREQUENCY RANGE By: MOHD AZIZ ARIS ERMEEY ABD KADIR PROF. DR ZAIKIAWANG PROF. MADYA AHMAD ISMAIL MAY 2010

2 SURAT PENYERAHAN LAPORAN Tarikh: May 2010 No. Fail Projek : 600-IRDC/ST/FRGS 5/3/1308 Penolong Naib Canselor (Penyelidikan) Institut Pengurusan Penyelidikan Universiti Teknologi MARA Shah Alam Ybhg. Prof LAPORAN AKHIR PENYELIDIKAN "NONDESTRUCTIVE AND NONCONTACT DIELECTRIC MEASUREMENT METHODS FOR TRANSFORMER OIL USING FREE SPACE MICROWAVE MEASUREMENT SYSTEM IN GHZ FREQUENCY RANGE" Merujuk kepada pekara di atas, bersama-sama ini disertakan 3 (tiga) salinan laporan akhir penyelidikan bertajuk "Nondestructive and noncontact dielectric measurement methods for transformer oil using free space microwave measurement system in ghz frequency range" Sekian, terima kasih. Ketua kumpulan penyelidik ii

3 RESEARCH TEAM MEMBER MOHD AZIZ ARIS ERMEEY ABD KADIR Research Member PROF. DR ZAIKIAWANG Research Member Signature PROF. MADYA AHMAD ISMAIL iii

4 ACKNOLEDGEMENT I would like to extend sincere appreciation to all project members Mr. Ermeey Abd Kadir, Assoc. Prof Ahmad Ismail and Prof. Dr. Zaiki Awang, head of the Microwave Technology Centre (MTC) department for their cooperation to accomplish the objective of the project and again, for Prof. Dr Zaiki Awang for his permission to use MTC's laboratory. Also thanks to all administrative and technical staff of MTC and Faculty of Electrical Laboratory, and my best friend Madam Noor Hasimah Baba for his guidance and editing of our research. I would also like to extend special thanks to Director of Universiti Teknologi MARA Terengganu, Deputy Director of Academic Affair Hajah Wan Dorishah Wan Abdul Manan, Deputy Director of Research and Indusitry Linkages Assoc. Prof Dr Azmi Che Hamid for their support. Deep gratitude is also extended to all staff Faculty of Electrical Engineering University Technology MARA Terengganu. My sincere gratitude to Almighty Allah S.W.T for his guidance that made the completion of our research. iv

5 TABLE OF CONTENT CONTENT SURAT PENYERAHAN LAPORAN RESEARCH TEAM MEMBER AKNOWLEDGEMENT LIST OF FIGURE LIST OF TABLE LIST OF ABBREVATIONS LIST OF SYMBOLS ABSTRACT PAGE ii iii iv ix xi xii xiii xv CHAPTER 1 INTRODUCTION 1 Problem Statements 3 Objectives of research 4 Scope of Work 4 Significance of study 5 Overview of the research 5 CHAPTER 2 LITERATURE REVIEW Introduction Measurement Technique 9 v

6 2.2.1 Free-space technique Resonant technique Waveguide technique Measurement Techniques in Microwave Systems 11 For Liquids Transformer Oil Measurement 12 CHAPTER 3 MATERIAL THEORY IN MICROWAVE FREQUENCIES Introduction Polarization Electronic Polarization Ionic or atomic Polarization Molecular Polarization Microwave and Material Interaction Permittivity Propagation of Wave in Dielectric Materials Liquids 23 CHAPTER 4 TRANSFORMER OIL 4.0 Introduction Oil Characteristics as an Insulator Physical Characteristics Molecular Characteristics Contaminant Removal 29 vi

7 4.3 Low Temperature Characteristics Behavior at Low Temperatures Dielectric characteristics 40 CHAPTER 5 METHODOLOGY 5.1 Metal Back Method Instruments Vector Network Analyzer Pair of Focusing Antenna Personal computer Sample Containers Measurement Setup Calibration Using Thru-Reflect-Line (TRL) Thru Reflect Line Gating Measurement Error Data Collection Procedure 67 CHAPTER 6 RESULTS AND DISCUSSIONS 6.1 Results Discussions 84 vii

8 CHAPTER 7 CONLUSIONS AND FUTURE RECOMMENDATION 7.1 Conclusion 6.2 Suggestion for Future Research BIBLIOGRAPHY CARTA PERLAKSANAAN PERANCANGAN PENYELIDIKAN APPENDICES viii

9 LIST OF FIGURES FIGURES TITLE PAGE Figure 3.1 Figure 3.2 Figure 3.3 Figure 5.1 Figure 5.2 Schematic Illustration of type of polarization in dielectric materials in microwave frequency 16 Frequency response of dielectric constant and loss factor for dielectric materials 17 A plot of Debye relaxation equation for water at 25 degree Celsius 24 Schematic diagram for metal back method For metal-plexiglas-sample-plexiglas layers 47 Flowchart for finding complex permittivity, dielectric constant and loss factor by metal back method 51 Figure 5.3 Vector network analyzer model 37269B 53 Figure 5.4 A pair of focusing antenna 54 Figure 5.5 Personal computer for data collection 55 Figure 5.6 Schematic diagram for Plexiglas container 56 Figure 5.7 Photograph for Plexiglas container 56 Figure 5.8 Figure 5.9 Schematic diagram of free-space microwave measurement system 58 Photograph of free-space microwave measurement system 58 Figure 5.10 TRL uses a thru, reflect and line standard 63 Figure 5.11 Sample holder mounted at the common focal plane ix

10 for holding Plexiglas container which contains liquid sample...65 Figure 5.12 Sample preparation 67 Figure 5.13(a) Graph data captured 68 Figure 5.13 (b) Tabular data captured 69 Figure 5.14 Figure 5.15 Complex permittivity of liquid sample calculated using metal-back method 70 Result from FORTRAN program to calculate complex permittivity of sample using metal-back method 71 Figure 6.1 Dielectric constant for sample 1 73 Figure 6.2 Loss tangent for sample 1 73 Figure 6.3 Dielectric constant for sample 2 76 Figure 6.4 Loss tangent for sample 2 76 Figure 6.5 Dielectric constant for sample 3 79 Figure 6.6 Loss tangent for sample 3 79 Figure 6.7 Dielectric constant for sample 4 81 Figure 6.8 Loss tangent for sample 4 82 Figure 6.9 Dielectric constant for four new transformer oil 84 Figure 6.10 Loss tangent for four new transformer oil 85 x

11 LIST OF TABLES TABLES TITLE PAGE Table 4.1 Table 4.2 Mineral Transformer Oil: Typical Molecular characteristics 28 Mineral Transformer Oil: Electric Characteristic Limits New Oil As Received and In Equipment 42 Table 6.1 Tabular data for sample Table 6.2 Tabular data for sample Table 6.3 Tabular data for sample Table 6.4 Tabular data for sample xi

12 LIST OF ABBREVATIONS VNA MTC NDT MNDT FSMM - Vector Network Analyzer - Microwave Technology Center - Nondestructive Testing - Microwave Nondestructive Testing - Free-space Measurement Systems xii

13 LIST OF SYMBOLS s 0 =8.854x10 n F!m - Permittivity in free-space Mo = 1.257x10 6 H lm- Permeability in free-space - Relative permittivity of a medium * M - Relative permeability of a medium X X Q - Wavelength of transmitted signal - Wavelength in free-space tan 8 - Loss tangent r T V - Reflection coefficient - Transmission coefficient - Del operator S. - Skin depth CT CO p D X E H - Conductivity - Angular frequency Irf - Polarization - Flux displacement - Susceptibility - Electric field - Magnetic field

14 s' - Dielectric constant E" - Loss factor k Q - Wavenumber in free-space k Z sn Y - Wavenumber in a medium - Normalized characteristic impedance - Propagation constant in the material - Permittivity in the high frequency limit s s - Permittivity in the low frequency limit T r - Temperature in Kelvin - Relaxation time / - Frequency GHz MHz S u S 22 S l2 S 2l - Frequency in Gigahertz - Frequency in Megahertz - Input reflection coefficient - Output reflection coefficient - Reverse transmission coefficient - Forward transmission coefficient xiv

15 ABSTRACT Knowledge of wideband dielectric properties of liquid materials is necessary in many applications such as biomedical, remote sensing, powder technology and radar absorbing materials. Nondestructive, noncontact, in SITU and real time measurement of dielectric properties of liquids is important for evaluation of complex material systems such as service-aged transformer oil. Free-space microwave measurement (FSMM) system (which is nondestructive and noncontact) was developed for accurate measurement of dielectric properties of low-loss and high-loss liquids at microwave frequencies. The purpose of this research is to measure the dielectric properties of transformer oil by using free-space microwave measurement system between GHz (K-band), to compare measured results with published results for transformer oil and to collect the variation values of dielectric properties in microwave frequency between 18GHz to 26GHz (k-band). FSMM system consists of spot focusing horn lens antennas, mode transitions, coaxial cables and vector network analyzer (VNA). Dielectric constants and loss factors were measured for new transformer oil and all results close agreed with published data. It is observed that metal-back method is suitable for dielectric measurement of transformer oil. xv

16 CHAPTER 1 INTRODUCTION 1.1 General Material characterization is a process to identify or describe the properties of any single material. This process represents many different disciplines, depending upon the background of the user. These concepts vary from scientist or researchers, who thinks of its atomic terms, for process engineer, the group who thinks of it in terms of properties, procedures, and also for quality assurance. The process has been explored many years back and knowledge in material characterization help many researchers, scientists and many others who are trying to identify and classify any single material they want to use. Thermal, electrical and mechanical are few examples of material properties that primarily provide the information about composite, structure, and defects of a material. In material characterization process, especially dealing with electrical properties many types of techniques are applied such as ultrasound method, laser method, microwave method for high frequency region and laboratory conducting experiments for low frequency region. These methods promise high precision and efficient technique if well conducted (Ulaby, 2004). This research is focused on the evaluation of an electrical properties of transformer oil and microwave measurement methodology. In material science engineering, the electrical properties of a material give information about the behavior and responses of a material against any measurements. Basically electrical properties of material is represented as permittivity comprise of dielectric constant and loss 1

17 tangent. Permittivity is determined by the ability of a material to polarize in response to an applied electric field. The interesting discussion about properties of material is that the electrical properties for each material is different from each other. Therefore, a material can be identified according to its electrical properties either solid or liquid material. (Ulaby,2004,2005) and (Pozar, 2005), refers "Microwaves" as an alternating current signals with frequencies between 300 MHz to 300 GHz. The field of microwave engineering is often considered as a very mature discipline because the fundamental concepts of electromagnetic were developed over 100 years ago. Most of applications of today's microwave technology are applied in communications systems, radar systems, environmental remote sensing and medical systems. Radar systems are applied in military, commercial, scientific systems and industrial applications. Radar is used for detecting and locating ground and seagoing targets such as submarine, as well as for missile guidance and fire control. In the commercial sector, radar technology is used for air traffic control, motion detector (door opener and security alarms), and distance measurements. Scientific applications of radar include remote sensing in the atmosphere, the oceans, the grounds, medical diagnostic and therapy. Microwave is applied in medical field such as microwave imaging of human body for cancer detection. In industries, microwave is widely used for heating, drying and also defect detection. The increasing trend in the manufacturing of dielectric materials, coupled with the noncontact and high speed advantages of microwave testing, can lead to further investigation on applications to obtain accurate permittivity measurement as a function of frequency. Yu. et al. (2000) found that accurate microwave methods for complex permittivity measurements are also needed in the investigation of bio-

18 materials and for applications in medicine and industry. In 1948, C. L. Liskow was the first person to discuss the use of microwaves for testing of industrial materials. Later, several microwave techniques for exploring the properties and dimensions of materials were reported between 1948 and the early 1960s. Numerous papers describing methods and applications in microwave nondestructive testing have been published since early 1960s as has been shown by (J., W, J, & C, 1986), (B.G.M, 1990), and (Moradi and Ghorbani, 2002). 1.2 Problem Statement Recently, there has been an increasing need for a nondestructive and noncontact method of complex permittivity measurement for different dielectric materials. The evaluation and characterization of liquids, especially, chemically active reagents and solvents give problems to many industries due to the hazardous effects of these reagents and solvents on people. The present conventional techniques are mostly contacting and destructive. Therefore, the nondestructive and noncontact evaluation is highly desirable for these kinds of liquid. When the noncontact technique is implemented the high risk of chemical liquids on employers can be reduced. In some applications, the liquid has additional important functions, for example, it acts as a heat-transfer agent in transformers for electrical power delivery. It is important to make frequent inspections to evaluate the deterioration of the liquid insulator. This is because an increase of moisture content in the liquids can cause the liquid insulator to breakdown and lead to possibly high explosion. An increase in moisture content will cause higher dielectric loss due to formation of electric dipole. These dielectric losses have contributions to the permittivity of liquid. Therefore, for inspection purposes of noncontact, portable and easily handled equipment is needed to analyze the liquid. In 3

19 this research, a microwave nondestructive technique will be studied and developed based on free-space techniques. The rationale for this research is based on the problem highlighted above. It is observed that free-space techniques can be used to evaluate transformer oil on site or laboratory based analysis. 1.3 Objective 1. To measure the dielectric properties of transformer oil by using free-space microwave measurement system between 18GHz to 26GHz (K-band). 2. To compare measured results with published results for transformer oil. 3. To collect the variation values of dielectric properties in microwave frequency between 18GHz to 26GHz (k-band). 1.4 Scope of Work In order to accomplish objectives of the research, the scopes of study are listed as follow: 1. Review the literature of previous and present free-space techniques to evaluate the dielectric properties of transformer oil such as reflection and transmission method, transmission only method and metal back method. 2. Review the literature of the previous and present technique to evaluate the dielectric properties of transformer oil based on waveguide, coaxial line and cavity resonator techniques for value comparison purposes. 4

20 3. Measure dielectric properties of new and used transformer oil. The measurement will be carried out ranging from 18.0 to 26.0 GHz of frequency at a temperature of 20 C. 4. Design and develop laboratory experimental tests for measurement of transformer oil using FSMM system. 5. Compare experimental results with published data for dielectric properties of transformer oil. 1.5 Significance of Study In this research effort, free-space techniques are developed based on the following reasons: 1. Free-space technique is nondestructive and noncontact, therefore, dielectric properties of any liquids such as chemical active reagents can be evaluated easily either under high or low temperature conditions. 2. To minimize the high risk on employees who are involved in chemical liquids composition testing in industries. 3. The free-space technique can be implemented for onsite characterizations, for example, measuring dielectric properties of transformer oil which is used for heat transfer agent for transformer electrical power delivery. 1.6 Overview of the Research In Chapter Two, several types of microwave techniques in evaluating dielectric properties of liquids are reviewed. The advantages of free-space technique as compared to other techniques to characterize liquid sample are also discussed. 5

21 Chapter three presents the electromagnetic and dielectric properties of materials. This includes polarization, propagation of waves, liquids and interaction between microwave and liquid. This chapter also covers the transformer oil, properties and measurement technique to evaluate the deterioration of transformer oil. Chapter four describes measurement techniques and instruments used in this research. It covers reflection and transmission method, transmission only method and metal back method. All instruments involve in this research are introduced in this chapter, such as Vector Network Analyzer, two spot focusing antennas and fabricated sample holders (containers). Methods for calculating the complex permittivity of transformer oil using three computer programs are described. Lastly the measurement and data collection procedure for this research are also presented. Results and discussion of the experimental works are explained and discussed in Chapter Five. All the results are presented in graphs and tabular data forms. Comparisons of results with other techniques are also included in this chapter. Finally, Chapter Six summarizes the findings and offers conclusions and suggestions for future research. 6

22 CHAPTER 2 LITERATURE REVIEW 2.1 Introduction The study of material properties in microwave frequencies and the development of functional microwave materials have always been among the most active areas in solidstate physics, materials science, electrical and electronic engineering (Ghodgaonkar et el. 1990). In recent years, the demand for the development of high speed, high frequency circuits and systems requires complete understanding of the properties of material functioning at microwave frequencies. These aspects make the characterization of materials properties become an important field in microwave measurement systems. In a paper by B. G. M. Helme (1990), the accurate measurement of dielectric properties, with the frequency within a range of 300 MHz to 300 GHz is important for the following reasons: 1. Precise knowledge of microwave properties of materials is required for the design and development of microwave systems and components. 2. Microwaves also have been widely used in industrial applications such as drying, curing and sintering of materials such as timber, food grains, paper, and ceramics. Therefore, knowledge of microwave properties of these materials is required. 3. There is also an increasing use and application of microwaves in fusion, biological and medical studies. Therefore, it is important to know properties of materials used in these applications. 7

23 Many different methods or techniques have been developed for the measurement of microwave dielectric properties of materials. At microwave frequencies, these methods involve measurement of reflection and transmission properties of materials in coaxial, waveguide, cavity or free-space media. Techniques have been developed which uses many different shapes of samples such as thin rods and fibers, circular and annular disc, thin films, liquids, powders and irregularly shaped objects. For dielectric measurements, coaxial line technique, waveguide technique, cavity technique and free-space technique are widely used. These techniques can calculate parameters such as complex permittivity and complex permeability of dielectrics from measured microwave properties. B. G. M. Helme (1990) and Note (1992)found the use of any particular technique depends on physical and chemical nature of the sample. According to K. A. Jose (2001) and Gholamreza et al. (2002), the microwave measurement methods can be divided into two categories, namely, destructive or nondestructive. In destructive technique such as the waveguide technique or resonant cavity, it is necessary to cut the sample so that it fits the waveguide cross section with negligible air gaps. Thus, this type of sample preparation is destructive and time consuming; because it requires a small part or cutout of a sample. Furthermore, it will not represent the actual volume of tested material. Inversely a non-destructive technique refers to the test methods used to examine an object, material or system without impairing its future usefulness. Also, there is no limitation on amount and structure of required materials in any application. Therefore the huge sample of dielectric material still can be measured to identify its properties without cutting it into small size. 8

24 2.2 Measurement Technique Free-Space Measurement Setup As be shown by Ghodgaonkar et al. (1990, 2000), Free-space techniques can be applied over a wide range of frequencies. The free-space measurement system was presented for the measurement of dielectric properties in the frequency range of 14.5 GHz GHz. They were measured using the solid sample like a timber and concrete to identity the moisture content in those samples (Ghodgaonkar, 1990). Free-space techniques for electrical property measurements are preferred over cavity and waveguide methods for the following reasons: 1. Materials such as ceramics, composites, and others are inhomogeneous due to variations in manufacturing processes. Because of inhomogeneity, the unwanted higher order modes can be excited at dielectric interface in waveguides and cavities. 2. Dielectric measurements using free-space techniques are nondestructive and noncontact. Because of this feature, these methods are particularly suitable for dielectric measurements under high or low temperature conditions and complex electromagnetic environmental conditions (e.g. D. C. biasing fields, ionizing radiations and others). 3. In the cavity and waveguide methods, it is necessary to cut the sample to fit the waveguide cross section with negligible air gaps. This requirement will limit the accuracy of measurements for material, which cannot be cut precisely. 9