POTENTIAL DISTRIBUTION OVER SUSPENSION INSULATORS … · suspension insulator string. The...

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

Misan University

College of Engineering

Electrical Engineering Department

مهداة إىل شهداء احلشد الشعبي واجليش العراقي

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:

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: Signature:

Name: Name:

Date: Date:

Signature: Signature:

Name: Name:

Date: Date:

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.

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.

1

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%.

2

TABLE OF CONTENTS

Abstract -----------------------------------------------------------------------------------------1

Table of contents-------------------------------------------------------------------------------2

List of Symbols---------------------------------------------------------------------------------4

List of Abbreviations--------------------------------------------------------------------------4

List of Figures----------------------------------------------------------------------------------4

List of Tables-----------------------------------------------------------------------------------5

Chapter One: General Introduction-------------------------------------------------------6

1.1 Introduction------------------------------------------------------------------------------7

1.2 Aim of project----------------------------------------------------------------------------7

1.3 Insulator materials-----------------------------------------------------------------------7

1.3.1 Porcelain--------------------------------------------------------------------------7

1.3.2 Glass-------------------------------------------------------------------------------8

1.4 Types of insulators----------------------------------------------------------------------9

1.4.1 Pin type insulators--------------------------------------------------------------9

1.4.2 Post insulators--------------------- -------------------------------------------- 10

1.4.3 Suspension type insulators---------------------------------------------------11

1.4.4 Strain insulators---------------------------------------------------------------12

1.4.5 Shackle insulators-------------------------------------------------------------12

1.5 Literature review-----------------------------------------------------------------------13

1.6 Scope of report-------------------------------------------------------------------------14

1.7 Outline of report--------------------------------------------------------------14

Chapter Two: Methodology----------------------------------------------------------------15

2.1 Potential distribution over suspension insulator string----------------------------16

2.2 String efficiency-----------------------------------------------------------------------18

2.3 Mathematical expression -------------------------------------------------------------18

2.4 Methods of Improving String Efficiency--------------------------------------------19

Chapter Three: Implementation----------------------------------------------------------21

3.1 Components of project----------------------------------------------------------------22

3.2 Implementation of potential distribution along suspension insulators string---22

3.2.1 Part -1- Determination of Voltage Distribution---------------------------23

3

3.2.2 Part -2- Improve the efficiency by using longer cross-arm--------------23

3.2.3 Part -3- Improve the efficiency by using guard ring ---------------------24

3.2.4 Part -4- Improve the efficiency by choose the suitable cross-arm

length and suitable guard ring-------------------------------------------------------25

Chapter Four: Results and Discussions -------------------------------------------------26

4.1 Result of part -1- -----------------------------------------------------------------------27

4.2 Result of part -2- -----------------------------------------------------------------------28

4.3 Result of part -3- -----------------------------------------------------------------------29

4.4 Result of part -4- -----------------------------------------------------------------------30

4.5 Results of project by simulation in multisim---------------------------------------31

4.6 Compare between practically, theoretically and simulation Results -----------35

4.7 Discussions-----------------------------------------------------------------------------37

Chapter Five: Conclusion and Future Work-------------------------------------------38

5.1 Conclusion-------------------------------------------------------------------------------39

5.2 Future Work-----------------------------------------------------------------------------39

REFERENCES

4

I Current

𝐱𝐜 Capacitance reactance

𝛚 Angular frequency

ɳ Efficiency

Ic Capacitance current

AC Alternating current

V Voltage

K Capacitance ratio

F Frequency

Ma Mille ampere

µF Micro farad

Fig. 1.1. Toughened glass insulator and Porcelain insulator 8

Fig. 1.2. Pin type insulator 9

𝐅𝐢𝐠. 𝟏. 𝟑. Post Insulators 10

𝐅𝐢𝐠. 𝟏. 𝟒. Two post insulators linked together 10

𝐅𝐢𝐠. 𝟏. 𝟓. Suspension type insulators 11

𝐅𝐢𝐠. 𝟏. 𝟔. The strain insulator 12

𝐅𝐢𝐠. 𝟏. 𝟕. The shackle insulator 13

𝐅𝐢𝐠. 𝟐. 𝟏. Potential distribution over suspension insulator string 16

𝐅𝐢𝐠. 𝟐. 𝟐. Flow Chart of Methodology 17

5

𝐅𝐢𝐠. 𝟐. 𝟑. Grading ring 20

𝐅𝐢𝐠. 𝟑. 𝟏. Implementation of potential distribution along

suspension insulators string

22

𝐅𝐢𝐠. 𝟑. 𝟐. Implementation of part-1- & part-2- 24

𝐅𝐢𝐠. 𝟑. 𝟑. Implementation of part-3- & part-4- 25

𝐅𝐢𝐠. 𝟒. 𝟏. Simulation of part-1- 31

𝐅𝐢𝐠. 𝟒. 𝟐. Simulation of part-2- 32

𝐅𝐢𝐠. 𝟒. 𝟑. Simulation of part-3- 33

𝐅𝐢𝐠. 𝟒. 𝟒. Simulation of part-4- 34

Table 4.1. Practically results of part -1- 27

Table 4.2. Theoretically results of part -1- 27

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟑. Practically results of part -2- 28

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟒. Theoretically results of part -2- 28

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟓. Practically results of part -3- 29

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟔. Theoretically results of part -3- 29

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟕. Practically results of part -4- 30

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟖. Theoretically results of part -4- 30

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟗. Simulation results of part -1- 31

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟏𝟎. Simulation results of part -2- 32

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟏𝟏. Simulation results of part -3- 33

𝐓𝐚𝐛𝐥𝐞 𝟒. 𝟏𝟐. Simulation results of part -4- 34

CHAPTER ONE GENERAL INTRODUCTION

6

CHAPTER ONE

GENERAL INTRODUCTION

1.1 Introduction

1.2 Aims of project

1.3 Insulator materials

1.3.1 Porcelain

1.3.2 Glass

1.4 Types of insulators

1.4.1 Pin type insulators

1.4.2 Post insulators

1.4.3 Suspension type insulators

1.4.4 Strain insulators

1.4.5 Shackle insulators

1.5 Literature review

1.6 Scope of report

1.7 Outline of report


7

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]..

1.2 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. 1.1.

1.3.1 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%


8

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].

1.3.2 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. 1.1. Toughened glass insulator and Porcelain insulator [9].


9

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].

1.4.1 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. 1.2. 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.


10

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.

1.4.2 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. 1.3. 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. 1.4. Conductor is fixed on the top of the insulator

with help of connector clamp [3].

Fig. 1.3. Post Insulators [10].

Fig. 1.4. Two post insulators linked together.


11

1.4.3 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. 1.5.

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. 1.5. 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.


12

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.

1.4.4 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. 1.6.

Fig. 1.6. The strain insulator [10].

1.4.5 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


13

a bolt or to the cross-arm. Fig. 1.7. shows the shackle insulator. The conductor in the

groove is fixed with a soft binding wire [6].

Fig. 1.7. 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


14

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.

CHAPTER TWO METHODOLOGY

15

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


16

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 C1. 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), V3will be much more than V2or

V1. (where C is self-capacitance and C1is air-capacitance) [6].

(i) (ii) (iii)

Fig. 2.1. Potential distribution over suspension insulator string [6].


17

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. 2.2.

Fig. 2.2. Flow Chart of Methodology

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


18

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 C1 is

some fraction K of self-capacitance, C1 = KC. Starting from the cross-arm or tower,

the voltage across each unit is V2, V2 and V3 respectively as shown [6].

I2 = I1 + i1

V2ωC = V1ωC + V1ωC1 (C1 = KC)

V2ωC = V1ωC + V1ωKC

V2 = V1(1 + K) ………………. (1)

I3 = I2 + i2

V3ωC = V2ωC + (V1 + V2)ωC1

V3ωC = V2ωC + (V1 + V2)ωKC

V3 = V2 + (V1 + V2)K


19

V3 = KV1 + V2(1 + K)

V3 = V1(1 + 3K + K2) ………………. (2)

Voltage between conductor and earth (tower) is:

V = V1 + V2 + V3

Note:

V4 = V1(1 + 6K + 5K2 + K3)

V5 = V1(1 + 10K + 15K2 + 7K3 + K4)

V = V1 + V2 + V3 + V4 + V5

Vn+1 = (V1 + V2 + V3 + ⋯ + Vn−1)K + Vn(1 + K) (where n is number of disc).

V = V1 + V2 + ⋯ + Vn

ƞ =V

nxVn

Also, there is another method (general method) to solve problems, where

Vx = 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


20

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. 2.3. 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 i1, i2 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]

CHAPTER THREE IMPLEMENTATION

21

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

3.2.1 Part -1- Determination of Voltage Distribution

3.2.2 Part -2- Improve the efficiency by using longer cross

arm

3.2.3 Part -3- Improve the efficiency by using guard ring

3.2.4 Part -4- Improve the efficiency by choose the suitable

cross-arm length and suitable guard ring


22

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 0.055 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. 3.1.

Fig. 3.1. Implementation of potential distribution along suspension insulators string


23

3.2.1 Part -1- Determination of Voltage Distribution

1. Connect the circuit of insulator string model in Fig. 3.2.

Take C= 1 µF

Take Co= 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.

3.2.2 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 Co= 0.1 C (K=0.1)








24

Fig. 3.2. Implementation of part-1- & part-2-

3.2.3 Part -3- Improve the efficiency by using guard ring


Take C= 1 µF

Take Co= 0.22 C (K= 0.22)

Take C1 = 0.055 C , C2 = 0.146 C , C3 = 0.33 C , C4 = 0.88 C








25

3.2.4 Part -4- Improve the efficiency by choose the suitable cross-arm

length and suitable guard ring


Take C= 1 µF

Take Co= 0.1 C (K= 0.1)

Take C1 = 0.025 C , C2 = 0.067 C , C3 = 0.15 C , C4 = 0.4 C







Fig. 3.3. Implementation of part-3- & part-4-

CHAPTER FOUR RESULTS AND DISCUSSION

26

CHAPTER FOUR

Results and Discussions

4.1 Result of part -1-




4.5 Results of project by simulation in multisim

4.6 Compare between practically, theoretically and simulation Results of

project

4.7 Discussions


27


When K=0.22

Table 4.1 Practically results of part -1-

Table 4.2 Theoretically results of part -1-

Note: 𝐈𝐜 =𝐕

𝐱𝐜 , 𝐱𝐜 =

𝟏

𝛚𝐜=

𝟏

𝟐𝛑𝐟 , f=50Hz


28


When K=0.1




29


When K=0.22 C1 = 0.055 C , C2 = 0.146 C , C3 = 0.33 C , C4 = 0.88 C




30


When K=0.1 C1 = 0.025 C , C2 = 0.067 C , C3 = 0.15 C , C4 = 0.4 C




31

4.5 Results of project by simulation in multisim

Fig 4.1 Simulation of part-1-

Table 4.9 Simulation results of part -1-


32




33




34




35

4.6 Compare between practically, theoretically and simulation Results

of project

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5

VO

LTA

GE(

V)

NO. OF INSULATOR

PART-1-

Practically

Theoretically

Simulation

0

1

2

3

4

5

6

7

8

1 2 3 4 5

VO

LTA

GE(

V)

NO. OF INSULATOR

PART-2-

Practically

Theoretically

Simulation


36

0

1

2

3

4

5

6

1 2 3 4 5

VO

LTA

GE(

V)

NO. OF INSULATOR

PART-3-

Practically

Theoretically

Simulation

0

1

2

3

4

5

6

1 2 3 4 5

VO

LTA

GE(

V)

NO. OF INSULATOR

PART-4-

Practically

Theoretically

Simulation


37

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.


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.


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.

53.76

68.56

98 100

52.63

67.02

99.98 100

52.48

66.92

100 100

0

20

40

60

80

100

120

Part-1- Part-2- Part-3- Part-4-

Effi

cie

ncy

%

PARTS

Practically Theoretically Simulation

CHAPTER FIVE CONCLUSION AND FUTURE WORK

38

CHAPTER FIVE

CONCLUSION AND FUTURE WORK

5.1 Conclusion

5.2 Future Work

CHAPTER FIVE CONCLUSION AND FUTURE WORK

39

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.

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, 2006 12th Biennial, 05 June 2006.

[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, 2006 12th Biennial, 30 April-3 May 2006.

[3] B.R. GUPTA, "POWER SYSTEM ANALYSIS AND DESIGN", in RAM NAGAR, NEW

DELHI-110055, FIFTH EDITION, 2008, chapter Four.

[4] Abhijit Chakrabarti and Sunita Halder, "POWER SYSTEM ANALYSIS OPERATION AND

CONTROL", Third Edition, 2011, New Delhi-110001, 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-110002, First edition 2006,

chapter 12.

[9] https://www.electrical4u.com/electrical-insulator-insulating-material-porcelain-glass-polymer-

insulator.

[10] https://www.electrical4u.com/strain-insulator.gif.

http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=10874

http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=10874

https://www.electrical4u.com/electrical-insulator-insulating-material-porcelain-glass-polymer-insulator



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