POTENTIAL DISTRIBUTION OVER SUSPENSION INSULATORS STRING

Transcription

1 Misan University College of Engineering Electrical Engineering Department POTENTIAL DISTRIBUTION OVER SUSPENSION INSULATORS STRING BY AHMED SHAKER ABDUL LATEEF ALI ABDUL SATTAR MAHDI BILAL ALI ABDUL RIDHA FIRDAUS KAREEM A project report submitted to the Department of Electrical Engineering College of Engineering /Misan University in partial fulfilment of the requirements for the award of the degree of Bachelor of Electrical Engineering 2017

2 مهداة إىل شهداء احلشد الشعبي واجليش العراقي

3 APPROVAL FOR SUBMISSION I certify that this project report entitle " POTENTIAL DISTRIBUTION OVER SUSPENSION INSULATORS STRING " was prepared by (AHMED SHAKER ABDUL LATEEF, ALI ABDUL SATTAR MAHDI, BILAL ALI ABDUL RIDHA, FIRDAUS KAREEM) has met the required standard for submission in partial fulfilment of the requirements for the award of Bachelor of Electrical Engineering at University of Misan Approved by: Signature: Supervisor: Date:

4 Certificate of Examiners We certify, as an examining committee, that we have read this project report entitled " POTENTIAL DISTRIBUTION OVER SUSPENSION INSULATORS STRING " examined the students (AHMED SHAKER ABDUL LATEEF, ALI ABDUL SATTAR MAHDI, BILAL ALI ABDUL RIDHA, FIRDAUS KAREEM) in its contents and found the project meets the standard for degree of B.Sc. in Electrical Engineering. Signature: Name: Date: Signature: Name: Date: Signature: Name: Date: Signature: Name: Date:

5 ACKNOWLEDGEMENTS In the Name of Allah, Most Gracious, Most Merciful, praise and thank Allah, and peace and blessings are upon his Messenger. I would like to express my gratitude to the department of electrical engineering especially the head of the department Dr. Jabbar Raheem and to other teachers. I would like to express my great gratitude to my respected supervisor Assist Lect. Ameer Lateef Saleh for his invaluable advice and comments. constant encouragement, guidance, support, and patience all the way through my study work. Also special thanks to Dr. Ahmed R. Hussain, for his encouragement and helpful advice and for provide me the necessary references.

6 To my parents whose support and understanding helped to make this possible. I should not forget my brothers and sisters who have supported me to complete this project. Ahmed Shaker: I should not forget my dear wife who supported me by her wide heart and her pretty patience.

7 Abstract Insulators for overhead lines are considered to be of basic importance to the transmission system, through their ability to insulate the power lines as well as their function in carrying the weight of the line conductor. For higher voltages, a string of suspension insulators is used. The number of insulator units used depends on the voltages of the lines. The voltage is not equally shared between the units in a suspension insulator string. The capacitances between each cap/pin junction and the tower and between the cap and pin of each unit determine the voltage distribution. In this project, calculate the voltage distribution along a string of 5 suspension insulators, and determine the efficiency of string and we get efficiency equal to 53.76%. Then improve the efficiency of the string by Using a Longer Cross Arm and we get efficiency 68.56%. In this project also improve the efficiency again by using a guard ring. And we get efficiency equal to 98%. Finally, improve the efficiency by choose the suitable arm length and suitable guard ring and we get efficiency equal to 100%. 1

8 TABLE OF CONTENTS Abstract Table of contents List of Symbols List of Abbreviations List of Figures List of Tables Chapter One: General Introduction Introduction Aim of project Insulator materials Porcelain Glass Types of insulators Pin type insulators Post insulators Suspension type insulators Strain insulators Shackle insulators Literature review Scope of report Outline of report Chapter Two: Methodology Potential distribution over suspension insulator string String efficiency Mathematical expression Methods of Improving String Efficiency Chapter Three: Implementation Components of project Implementation of potential distribution along suspension insulators string Part -1- Determination of Voltage Distribution

9 3.2.2 Part -2- Improve the efficiency by using longer cross-arm Part -3- Improve the efficiency by using guard ring Part -4- Improve the efficiency by choose the suitable cross-arm length and suitable guard ring Chapter Four: Results and Discussions Result of part Result of part Result of part Result of part Results of project by simulation in multisim Compare between practically, theoretically and simulation Results Discussions Chapter Five: Conclusion and Future Work Conclusion Future Work REFERENCES 3

10 I x c ω ɳ Ic Current Capacitance reactance Angular frequency Efficiency Capacitance current AC Alternating current V Voltage K Capacitance ratio F Frequency Ma Mille ampere µf Micro farad Fig Toughened glass insulator and Porcelain insulator 8 Fig Pin type insulator 9 Fig Post Insulators 10 Fig Two post insulators linked together 10 Fig Suspension type insulators 11 Fig The strain insulator 12 Fig The shackle insulator 13 Fig Potential distribution over suspension insulator string 16 Fig Flow Chart of Methodology 17 4

11 Fig Grading ring 20 Fig Implementation of potential distribution along 22 suspension insulators string Fig Implementation of part-1- & part-2-24 Fig Implementation of part-3- & part-4-25 Fig Simulation of part-1-31 Fig Simulation of part-2-32 Fig Simulation of part-3-33 Fig Simulation of part-4-34 Table 4.1. Practically results of part Table 4.2. Theoretically results of part Table Practically results of part Table Theoretically results of part Table Practically results of part Table Theoretically results of part Table Practically results of part Table Theoretically results of part Table Simulation results of part Table Simulation results of part Table Simulation results of part Table Simulation results of part

12 CHAPTER ONE GENERAL INTRODUCTION CHAPTER ONE GENERAL INTRODUCTION 1.1 Introduction 1.2 Aims of project 1.3 Insulator materials Porcelain Glass 1.4 Types of insulators Pin type insulators Post insulators Suspension type insulators Strain insulators Shackle insulators 1.5 Literature review 1.6 Scope of report 1.7 Outline of report 6

13 CHAPTER ONE GENERAL INTRODUCTION 1.1 Introduction The overhead line conductors should be supported on the poles or towers in such a way that currents from conductors do not flow to earth through supports, line conductors must be properly insulated from supports. This is achieved by securing line conductors to supports with the help of insulators. The insulators provide necessary insulation between line conductors and supports and thus prevent any leakage current from conductors to earth [6]. In general, the insulators should have the following desirable properties: 1. High mechanical strength in order to withstand conductor load, wind load etc. 2. High electrical resistance of insulator material in order to avoid leakage currents to the earth [6]. 3. High relative permittivity of insulator material in order that dielectric strength is high [6]. 4. The insulator material should be non-porous, free from impurities and cracks otherwise the permittivity will be lowered [6]. 5. High ratio of puncture strength to flash over [6]. 6. They should not be porous [8] Aim of project 1. To study the potential distribution over a string of suspension insulators. 2. To determine the string efficiency. 3. To acquaint student methods of the string efficiency improvement. 1.3 Insulator materials The materials most commonly used for insulators of an overhead transmission line are porcelain and glass as shown in Fig Porcelain Porcelain is a ceramic material. A good electrical porcelain is free from internal laminations, holes and cracks. produced by firing a mixture of 20% silica, 30% 7

14 CHAPTER ONE GENERAL INTRODUCTION feldspar and 50% china clay at high temperature. It is mechanically stronger (but costlier than glass) and is used as a material to manufacture different types of insulators. Dust deposits and temperature changes normally do not affect much on its surface. The dielectric strength of porcelain is 60 KV per cm of thickness. A single porcelain unit can be used up to 33 kv. When used at low temperatures, the mechanical properties of the porcelain insulator are better but, at the same time, the material remains porous and may subsequently lead to dielectric failure [5] Glass Glass insulators are extensively used due to their lower costs, high dielectric strength (140 kv per cm of thickness) and simple design. It is very easy to detect any fault within them because of their optical transparency. When compared to porcelain, glass withstands higher mechanical stresses, has low thermal expansion and it may develop high resistivity after proper annealing. The major disadvantage of glass is that moisture condenses more readily on its surface and facilitate the accumulation of dirt deposit, thus giving a high chance of surface leakage. Hence, its use is limited to a voltage of about 33 kv [5]. Fig Toughened glass insulator and Porcelain insulator [9]. 8

15 CHAPTER ONE GENERAL INTRODUCTION 1.4 Types of insulator The successful operation of an overhead line depends to a considerable extent upon the proper selection of insulator. There are several types of insulators but the most commonly used are pin type, post type, suspension type, strain insulator and shackle insulator [6] Pin type Insulators A pin type insulator is small, simple in construction and cheap [3]. The part section of pin type insulator is shown in Fig. 1.2(i). The pin insulator gets its name from the fact that it is supported on a pin. The pin holds the insulator, and the insulator has the conductor tied to it. There is a groove on the upper end of the insulator for housing the conductor [6] that means the conductor is supported on the top of the insulator. The conductor passes through this groove and is bound by the annealed wire of the same material as the conductor as shown in Fig. 1.2(ii). Pin type insulators are used for transmission and distribution of electric power at voltages up to 33 KV [3]. (i) (ii) Fig Pin type insulator [6]. Advantages 1. is small, simple in construction and cheap [3]. 2. In many cases one pin insulator can do the work of two suspension insulators. 3. Since pin insulator rises the conductor above the cross arm, so the required height of tower is less. 9

16 CHAPTER ONE GENERAL INTRODUCTION Disadvantages 1. For operating voltage greater than 33KV, it uneconomical and size is also bulky [6]. 2. Once a pin insulator is failed short circuit can occur Post Insulators Post type insulators are usually used in substations for supporting the bus bars, and disconnecting switches in sub-stations. The Post Insulators are shown in Fig It uses for voltages up to 33KV and it can be single stag as well as multiple stags. A post insulator is similar to a pin type insulator but has a metal base and frequently a metal cap so that more than one unit can be mounted in series and we can link more one insulator together as shown in Fig Conductor is fixed on the top of the insulator with help of connector clamp [3]. Fig Post Insulators [10]. Fig Two post insulators linked together. 10

17 CHAPTER ONE GENERAL INTRODUCTION Suspension Type Insulators The cost of a pin insulators increases very rapidly with increase in line voltage. Therefore, this type of insulator is not economical beyond 33 KV. For high voltages ( < 33 KV), it is a usual practice to use suspension type insulators shown in Fig They consist of a number of porcelain discs connected in series by metal links in the form of a string. The conductor is suspended at the bottom end of this string while the other end of the string is secured to the cross-arm of the tower. Each unit or disc is designed for low voltage, Say 11 KV. The number of discs in series would obviously depend upon the working voltage. For instance, if the working voltage is 66 KV, then six discs in series will be provided on the string [6]. Fig Suspension type insulators [6]. Advantages [6] 1. Suspension type insulators are cheaper than pin type insulators for voltages beyond 33 kv. 2. Each unit or disc of suspension type insulator is designed for low voltage usually 11 KV Depending upon the working voltage, the desired number of discs can be connected in series. 3. If any disc is damaged, the whole string does not become useless because the damaged disc can be replaced by the sound one. 11

18 CHAPTER ONE GENERAL INTRODUCTION 4. The suspension arrangement provides greater flexibility to the line. The connection at the cross arm is such that insulator string is free to swing in any direction and can take up the position where mechanical stresses are minimum. 5. In case of increased demand on the transmission line, it is found more satisfactory to supply the greater demand by raising the line voltage than to provide another set of conductors. The additional insulation required for the raised voltage can be easily obtained in the suspension arrangement by adding the desired number of disc. 6. The suspension type insulators are generally used with steel towers. As the conductors run below the earthed cross-arm of the tower, therefore, arrangement provides partial protection from lightning Strain Insulators These are special mechanically strong suspension insulators and are used to take the tension of the conductors at the line terminations and at positions where there is a change in the direction of line. The discs of a strain insulator are in a vertical plane as compared to the discs of suspension insulator which are in a horizontal plane. One extra-long spans, viz., at river crossings, two or three strings of strain insulators, arranged in parallel, are often used [3]. The strain insulator is shown in Fig Fig The strain insulator [10] Shackle Insulators In early days, the shackle insulators were used as strain insulators. But now days, frequently used for low voltage distribution lines. Such insulators can be used either in vertical position or horizontal position. They can be directly fixed to the pole with 12

19 CHAPTER ONE GENERAL INTRODUCTION a bolt or to the cross-arm. Fig shows the shackle insulator. The conductor in the groove is fixed with a soft binding wire [6]. Fig The shackle insulator [8]. 1.5 Literature review This project is a made as a laboratory experiment for students by represent the suspension insulator string as a string of series capacitance due to the similarity between the insulator and the capacitance in the behavior. But there are many previous studies in this topic. Bo Zhang..,[1]: was numerical method to analyze the potential distribution along long ceramic insulator strings on the head of transmission tower is presented. The method uses charge simulation method and boundary element method to obtain the capacitances among insulators, transmission lines, and tower, and then uses circuit theory to analyze the potential exerted on each insulator. The potential distribution along insulator strings on the head of 750 kv transmission tower is analyzed. Vassiliki T. Kontargyri,[2]: The paper presents a study into the potential and electric field distribution along an insulator string, which is used for the suspension of 150 kv overhead transmission lines. In order to calculate the voltage distribution, a model of the insulator string was set up using OPERA, an electromagnetic analysis program based on the Finite Elements method. Simulation results have been compared with experiments which were successfully conducted in the High Voltage Laboratory of the National Technical University of Athens. The experimental procedure is also 13

20 CHAPTER ONE GENERAL INTRODUCTION presented in the paper and discrepancies between simulated results and experiment and discussed. 1.6 Scope of report This project report entitle (Potential distribution over suspension insulators string) studies the most commonly types of the overhead insulators and how the potential distribution over a string of suspension insulators. Also study how to determine the efficiency of the string and how to improve it by using longer cross arms, by grading the insulators and by using a grading ring. 1.7 Outline of report This report is divided into four different chapters. First chapter is for introduction and the type of insulators. As for the second chapter is explains the methodology and the mathematical expression and Methods of Improving String Efficiency. All the aim of the project and components of project and experiment results and simulation including the discussion is done on third chapter. The study will be discussed at the end of this report which is in fourth chapter of the report. 14

21 CHAPTER TWO METHODOLOGY CHAPTER TWO METHODOLOGY 2.1 Potential distribution over suspension insulator string 2.2 String efficiency 2.3 Mathematical expression 2.4 Methods of Improving String Efficiency 15

22 CHAPTER TWO METHODOLOGY 2.1 Potential distribution over suspension insulator string A string of suspension insulators consists of a number of porcelain discs connected in series through metallic links. Fig. 2.1 (i) shows 3-disc string of suspension insulators. The porcelain portion of each disc is in between two metal links. Therefore, each disc forms a capacitor C as shown in Fig. 2.1 (ii) This is known as mutual capacitance or self-capacitance. If there were mutual capacitance alone, then charging current would have been the same through all the discs and consequently voltage across each unit would have been the same V/3 as shown in Fig. 2.1 (ii). However, in actual practice, capacitance also exists between metal fitting of each disc and tower or earth. This is known as shunt capacitance C 1. Due to shunt capacitance, charging current is not the same through all the discs of the string. Therefore, voltage across each disc will be different. Obviously, the disc nearest to the line conductor will have the maximum voltage. Thus, referring to Fig. 2.1 (iii), V 3 will be much more than V 2 or V 1. (where C is self-capacitance and C 1 is air-capacitance) [6]. (i) (ii) (iii) Fig Potential distribution over suspension insulator string [6]. 16

23 CHAPTER TWO METHODOLOGY The following points may be noted regarding the potential distribution over a string of suspension insulators [6] : 1. The voltage impressed on a string of suspension insulators does not distribute itself uniformly across the individual discs due to the presence of shunt capacitance. 2. The disc nearest to the conductor has maximum voltage across it. As we move towards the cross-arm, the voltage across each disc goes on decreasing. 3. The unit nearest to the conductor is under maximum electrical stress and is likely to be punctured. Therefore, means must be provided to equalize the potential across each unit. 4. If the voltage impressed across the string were d.c, then voltage across each unit would be the same. It is because insulator capacitances are ineffective for d.c. The overall methodology is simplified by Fig Arrange 5 capacitors in suspension form Determine efficiency and the voltage distribution over capacitors string Methods of Improving String Efficiency Using longer cross arms By grading the insulators By using a grading ring Fig Flow Chart of Methodology 17

24 CHAPTER TWO METHODOLOGY 2.2 String efficiency As explained above, voltage is not uniformly distributed over a suspension insulator string. The disc nearest to the conductor has maximum voltage across it and, hence, it will be under maximum electrical stress. Due to this, the disc nearest to the conductor is likely to be punctured and subsequently, other discs may puncture successively. Therefore, this unequal voltage distribution is undesirable and usually expressed in terms of string efficiency. The ratio of voltage across the whole string to the product of number of discs and the voltage across the disc nearest to the conductor is called as string efficiency String efficiency = flashover voltage of the string n X flashover voltage of one unit = voltage across string n X voltage across lowermost disc String efficiency is an important consideration since it decides the potential distribution along the string. The grater the string efficiency, the more uniform is the voltage distribution. Thus 100% string efficiency is an ideal case for which the voltage across each disc will be exactly the same. Although it is impossible to achieve 100% string efficiency, yet efforts should be made to improve it as closed to this value as possible [6]. 2.3 Mathematical expression In the Fig. 2.2 shows the equivalent circuit for a 3-disc string. Let us suppose that self-capacitance of each disc is C. Let us further assume that shunt capacitance C 1 is some fraction K of self-capacitance, C 1 = KC. Starting from the cross-arm or tower, the voltage across each unit is V 2, V 2 and V 3 respectively as shown [6]. I 2 = I 1 + i 1 V 2 ωc = V 1 ωc + V 1 ωc 1 (C 1 = KC) V 2 ωc = V 1 ωc + V 1 ωkc V 2 = V 1 (1 + K). (1) I 3 = I 2 + i 2 V 3 ωc = V 2 ωc + (V 1 + V 2 )ωc 1 V 3 ωc = V 2 ωc + (V 1 + V 2 )ωkc V 3 = V 2 + (V 1 + V 2 )K 18

25 CHAPTER TWO METHODOLOGY V 3 = KV 1 + V 2 (1 + K) V 3 = V 1 (1 + 3K + K 2 ). (2) Voltage between conductor and earth (tower) is: V = V 1 + V 2 + V 3 Note: V 4 = V 1 (1 + 6K + 5K 2 + K 3 ) V 5 = V 1 (1 + 10K + 15K 2 + 7K 3 + K 4 ) V = V 1 + V 2 + V 3 + V 4 + V 5 V n+1 = (V 1 + V 2 + V V n 1 )K + V n (1 + K) (where n is number of disc). V = V 1 + V V n ƞ = V nxv n Also, there is another method (general method) to solve problems, where V x = V sinh(x k) sinh ((x 1) k) sinh(n k) ƞ = sinh(n k) n(sinh(n k) sinh ((n 1) k) Where x is the number of insulator that you need to get the voltage across it. 2.4 Methods of Improving String Efficiency The voltage distribution across an insulator string is not uniform. The units nearest to the line end are stressed to their maximum allowable value while those near the tower end are considerably under stressed resulting in a waste of insulating material. The string efficiency indicates the extent of this wastage. Though string efficiency can never be made 100 per cent, an improvement in its value is necessary to minimize the wastage [3]. Some methods to improve string efficiency are: 1. Using longer cross arms It is clear from the above mathematical expression of string efficiency that the value of string efficiency depends upon the value of k. lesser the value of k, the greater is the string efficiency. As the value of k approaches to zero, the string efficiency approaches to 100%. The value of k can be decreased by reducing the shunt 19

26 CHAPTER TWO METHODOLOGY capacitance. In order to decrease the shunt capacitance, the distance between the insulator string and the tower should be increased, longer cross-arms should be used. However, there is a limit in increasing the length of cross-arms due to economic considerations. 2. By grading the insulators In this method, voltage across each disc can be equalize by using discs with different capacitances. For equalizing the voltage distribution, the top unit of the string must have minimum capacitance, while the disc nearest to the conductor must have maximum capacitance. The insulator discs of different dimensions are so chosen that each disc has a different capacitance. They are arranged in such a way that the capacitance increases progressively towards the bottom. As voltage is inversely proportional to capacitance, this method tends to equalize the voltage distribution across each disc [6]. 3. By using a grading ring The potential across each unit in a string can be equalized by using a guard ring which is a metal ring electrically connected to the conductor and surrounding the bottom insulator as shown in Fig The guard ring introduces capacitance between metal fittings and the line conductor. The guard ring is connected in such a way that shunt capacitance currents i 1, i 2 etc. are equal to metal fitting line capacitance currents i 1, i 2 etc. The result is that the same charging current I flow throw each unit of string. Consequently, there will be uniform potential distribution across the units [6]. Fig. 2.3 Grading ring [6] 20

27 CHAPTER THREE IMPLEMENTATION CHAPTER THREE Implementation of Potential Distribution Along Suspension Insulators String 3.1 Components of project 3.2 Implementation of potential distribution along suspension insulators string Part -1- Determination of Voltage Distribution Part -2- Improve the efficiency by using longer cross arm Part -3- Improve the efficiency by using guard ring Part -4- Improve the efficiency by choose the suitable cross-arm length and suitable guard ring 21

28 CHAPTER THREE IMPLEMENTATION 3.1 Components of project 1. Breadboard. 2. Transformer 220/25 V AC. 3. Five capacitors 1 µf. 4. Four capacitors 0.22 µf. 5. Four capacitors 0.1 µf. 6. Capacitor µf. 7. Capacitor µf. 8. Capacitor 0.33 µf. 9. Capacitor 0.88 µf. 10. Capacitor µf. 11. Capacitor µf. 12. Capacitor 0.15 µf. 13. Capacitor 0.4 µf. 14. Junction wires. 3.2 Implementation of potential distribution along suspension insulators string In this section we represent the suspension insulators string in the form of capacitances in addition to the air capacitances as shown in fig Fig Implementation of potential distribution along suspension insulators string 22

29 CHAPTER THREE IMPLEMENTATION Part -1- Determination of Voltage Distribution 1. Connect the circuit of insulator string model in Fig Take C= 1 µf Take C o = 0.22 C (K= 0.22) 2. Connect 25 volt to the insulator string. 3. Measure using a multi-meter the voltage distribution along string model and the current through it, and calculate the efficiency. 4. Calculate theoretically the voltage distribution for 5-unit string of insulators and the current through it, and the efficiency. 5. Compare the measurement results with the calculations results Part -2- Improve the efficiency by using longer cross arm 1. Connect the circuit of insulator string model in Fig. 3.2 Take C= 1 µf Take C o = 0.1 C (K=0.1) 2. Connect 25 volt to the insulator string. 3. Measure using a multi-meter the voltage distribution along string model and the current through it, and calculate the efficiency. 4. Calculate theoretically the voltage distribution for 5-unit string of insulators and the current through it, and the efficiency. 5. Compare the measurement results with the calculations results. 23

30 CHAPTER THREE IMPLEMENTATION Fig Implementation of part-1- & part Part -3- Improve the efficiency by using guard ring 1. Connect the circuit of insulator string model in Fig. 3.3 Take C= 1 µf Take C o = 0.22 C (K= 0.22) Take C 1 = C, C 2 = C, C 3 = 0.33 C, C 4 = 0.88 C 2. Connect 25 volt to the insulator string. 3. Measure using a multi-meter the voltage distribution along string model and the current through it, and calculate the efficiency. 4. Calculate theoretically the voltage distribution for 5-unit string of insulators and the current through it, and the efficiency. 5. Compare the measurement results with the calculations results. 24

31 CHAPTER THREE IMPLEMENTATION Part -4- Improve the efficiency by choose the suitable cross-arm length and suitable guard ring 1. Connect the circuit of insulator string model in Fig. 3.3 Take C= 1 µf Take C o = 0.1 C (K= 0.1) Take C 1 = C, C 2 = C, C 3 = 0.15 C, C 4 = 0.4 C 2. Connect 25 volt to the insulator string. 3. Measure using a multi-meter the voltage distribution along string model and the current through it, and calculate the efficiency. 4. Calculate theoretically the voltage distribution for 5-unit string of insulators and the current through it, and the efficiency. 5. Compare the measurement results with the calculations results. Fig Implementation of part-3- & part-4-25

32 CHAPTER FOUR RESULTS AND DISCUSSION CHAPTER FOUR Results and Discussions 4.1 Result of part Result of part Result of part Result of part Results of project by simulation in multisim 4.6 Compare between practically, theoretically and simulation Results of project 4.7 Discussions 26

33 CHAPTER FOUR RESULTS AND DISCUSSION 4.1 Result of part -1- When K=0.22 Table 4.1 Practically results of part -1- Table 4.2 Theoretically results of part -1- Note: I c = V x c, x c = 1 ω c = 1 2πf, f=50hz 27

34 CHAPTER FOUR RESULTS AND DISCUSSION 4.2 Result of part -2- When K=0.1 Table 4.3 Practically results of part -2- Table 4.4 Theoretically results of part -2-28

35 CHAPTER FOUR RESULTS AND DISCUSSION 4.3 Result of part -3- When K=0.22 C1 = C, C2 = C, C3 = 0.33 C, C4 = 0.88 C Table 4.5 Practically results of part -3- Table 4.6 Theoretically results of part -3-29

36 CHAPTER FOUR RESULTS AND DISCUSSION 4.4 Result of part -4- When K=0.1 C1 = C, C2 = C, C3 = 0.15 C, C4 = 0.4 C Table 4.7 Practically results of part -4- Table 4.8 Theoretically results of part -4-30

37 CHAPTER FOUR RESULTS AND DISCUSSION 4.5 Results of project by simulation in multisim Fig 4.1 Simulation of part-1- Table 4.9 Simulation results of part -1-31

38 CHAPTER FOUR RESULTS AND DISCUSSION Fig 4.2 Simulation of part-2- Table 4.10 Simulation results of part -2-32

39 CHAPTER FOUR RESULTS AND DISCUSSION Fig 4.3 Simulation of part-3- Table 4.11 Simulation results of part -3-33

40 CHAPTER FOUR RESULTS AND DISCUSSION Fig 4.4 Simulation of part-4- Table 4.12 Simulation results of part -4-34

41 VOLTAGE(V) VOLTAGE(V) CHAPTER FOUR RESULTS AND DISCUSSION 4.6 Compare between practically, theoretically and simulation Results of project Practically Theoretically Simulation NO. OF INSULATOR PART-1- PART Practically Theoretically Simulation NO. OF INSULATOR 35

42 VOLTAGE(V) VOLTAGE(V) CHAPTER FOUR RESULTS AND DISCUSSION Practically Theoretically Simulation NO. OF INSULATOR PART-3- PART Practically Theoretically Simulation NO. OF INSULATOR 36

43 Efficiency % CHAPTER FOUR RESULTS AND DISCUSSION Part-1- Part-2- Part-3- Part-4- PARTS Practically Theoretically Simulation 4.7 Discussions We note from the result of part (1) that the voltage impressed on a string of suspension insulators does not distribute itself uniformly across the individual discs due to the presence of shunt capacitance and the efficiency is about 53 % as shown in table 3.1, that indicates that we have a loss in power. From part (2) we note that the voltage impressed on a string of suspension insulators is distribute more uniformly from part (1) and the efficiency is about 68 % as shown in table 3.3, that indicates that the loss in power is less than that in part (1) and efficiency is improved. From part (3) we note that the voltage impressed on a string of suspension insulators is distribute more uniformly from previous parts and the efficiency is about 98 % as shown in table 3.5, that indicates that the loss in power is less than that in previous parts and efficiency is improved. From part (4) we note that the voltage impressed on a string of suspension insulators is distribute uniformly by choose a suitable cross-arm length and suitable guard ring and we get efficiency about 100% as shown in table 3.7 and that what are we need to reduce the losses of power in transmission line to as little as possible. Note: These measurements and results by neglecting the ambient weather conditions and by assuming the circumstances of air ideal. 37

44 CHAPTER FIVE CONCLUSION AND FUTURE WORK CHAPTER FIVE CONCLUSION AND FUTURE WORK 5.1 Conclusion 5.2 Future Work 38

45 CHAPTER FIVE CONCLUSION AND FUTURE WORK 5.1 Conclusion The voltage impressed on a string of suspension insulators does not distribute itself uniformly across the individual discs due to the presence of shunt capacitance. The disc nearest to the conductor has maximum voltage across it. As we move towards the cross-arm, the voltage across each disc goes on decreasing hence the efficiency being low. As we decrease the length of the cross-arm the air capacitance will increase and the voltage will distribute more uniformly and the efficiency will be high. If we a guard ring, then the voltage will distribute more uniformly and in ideal condition the voltage will distribute uniformly (in this experiment each disc have five voltage) 5.2 Future Work Future researcher need to develop the study of the potential distribution over suspension insulators string. In order to simulate the transmission tower, proper stand need to be built so that it will simulate the real distribute of voltage that is exist in the real transmission tower. For the study of the potential distribution, the future researcher also needs to consider the study the effect of contamination to the performance of insulator time by time. 39

46 REFERENCES [1] Bo Zhang, Jinliang He, Rong Zeng, Shuiming Chen," Potential Distribution along Long Ceramic Insulator Strings on the Head of high Voltage Transmission Tower", IEEE Conference on Electromagnetic Field Computation, th Biennial, 05 June [2] Vassiliki T. Kontargyri1, Ioannis F. Gonos1, Ioannis A. Stathopoulos, " Measurement and Verification of the Voltage Distribution on High Voltage Insulators", IEEE Conference on Electromagnetic Field Computation, th Biennial, 30 April-3 May [3] B.R. GUPTA, "POWER SYSTEM ANALYSIS AND DESIGN", in RAM NAGAR, NEW DELHI , FIFTH EDITION, 2008, chapter Four. [4] Abhijit Chakrabarti and Sunita Halder, "POWER SYSTEM ANALYSIS OPERATION AND CONTROL", Third Edition, 2011, New Delhi , chapter 5, page 166. [5] S. Rao, M.E and MIE., ELECTRICAL SUBSTATION ENGIREERING &PRACTICE", third edition,2008, chapter 9, page 170. [6] V.K MEHTA ROHIT MEHTA, "PRINCIPLES OF POWER SYSTEM", FOURTH EDITION 2008, CHAPTER 8. [7] Colin Bayliss and Brian Hardy, " Transmission and Distribution Electrical Engineering", Fourth edition 2012, chapter 6, page 171. [8] R. K. Rajput, "A TEXTBOOK OF POWER SYSTEM ENGINEERING", in LAXMI PUPLICATION (P) LTD 113, Golden house, daryaganj, New Delhi , First edition 2006, chapter 12. [9] [10]