INVESTIGATION AND EVALUATION OF LOCAL LIQUID DIELECTRIC FOR POWER TRANSFORMER INSULATION: A CASE STUDY OF SOYBEAN OIL

TABLE OF CONTENTS

Title Page

Approval

Certification

Dedication

Acknowledgements

Abstract

Table Of Contents

List Of Figures

List Of Tables

List Of Symbols And Abbreviation

CHAPTER ONE: Introduction

1.0. Background of the Study

1.1. Statement of the Problem

1.2. Objectives of the Study

1.3. Scope of the Study

1.4. Significance of the Study

CHAPTER TWO: Literature Review

2.1   General overview of local liquid dielectric concepts

2.1.1 History of Ester Fluids as Dielectric Coolants

2.2   Basic concept of power transformer insulation level

2.2.1Transformer insulation

2.2.2 Ageing of oil

2.2.2.1. The Bathtub Curve Relationship

2.2.2.2 The accelerated thermal ageing process

2.2.3Dielectric testing (break down voltage)

2.3.4 Properties of liquid dielectric

2.3   Locally available oil base for liquid dielectric production

2.3.1. List of available local liquid

2.3.2.  Comparative  analysis  of  the  existing  conventional  liquid  and  the proposed Liquid dielectric on power transformer insulation

2.3.3 Properties of vegetable oil

2.4   Antioxidants for Soy Beans Oil

2.4.1The Nature and Mechanisms of the Operation of Antioxidant

2.4.2Oxidation in lubricant base oil

2.4.3Measuring oxidation in lubricant base oils

2.5.4Oxidation stability index of vegetable oil

CHAPTER THREE: Methodology Of Experiment Design

3.1. Inhabitation of the Soybean Oil: Material and Method

3.2. ACID VALUE (MgKOH/g)

3.3. VISCOSITY

3.4. Flash and Fire Point

3.5. Pour Points Tests

3.6. Subjecting the oil to Accelerated Ageing

3.7. Measurement of the Oil Breakdown Voltage

3.7.1. Breakdown Voltage Detection

3.7.2. Electrode Gap Setting

3.7.3. Breakdown Voltage Test

3.7.4. Assessing Validity of the Test Result

3.8. Measurement of the Oil Sample Dielectric Losses (tan )

3.9. Measurement of the Oil Sample Permittivity

CHAPTER FOUR

4.0. Result Data and Analysis

4.1. Result Data on the Physical and Chemical Properties of the Soybean Oil

4.2.2. Dielectric Dissipation Factor (Tan)

CHAPTER FIVE: Conclusions And Recommendations

5.1. Conclusions

5.2. Recommendations

5.3. Suggestion for Further Studies

REFERENCES

APPENDIX

ABSTRACT

This work investigates and evaluates local liquid dielectric for insulation of power transformers. Considering the importance of transformer insulation the investigation is borne out of the need to develop the capacity for local production of transformer dielectric. Natural esters of vegetables origin have been found to have the suitable dielectric properties for them to be used as replacement dielectric fluids for mineral oil. However vegetable oil has poor resistance to oxidation, hence the need for inhibiting the vegetable oil for use as insulation fluid. In this work inhibited locally extracted soybean oil (soybean oil treated with antioxidant) is subjected to accelerated ageing in order to determine its suitability as dielectric fluid. The properties of the soybean oil is investigated against standard and compared with those of mineral oil. The

investigated soybean meets acceptability specifications since the measured flash point is 257⁰C,

the pour point is -15⁰C, the acidity is low at 0.0027mgkoH/mg, its dissipation factor after ageing

is 12.11 x 10^-3 (which is within recommended units) and showed a high dielectric breakdown voltage (59.08kV). Results obtained showed that the inhabited soybean oil has properties comparable to those of mineral oil and is suitable for use as transformer dielectric fluid.

CHAPTER ONE

INTRODUCTION

1.0. Background of the Study

Electrical faults that occur in power transfers accounts for over fifty percent of transformer failure’s expenditures . Fifty percent of transformer failure’s expenditure is caused by insulation, dielectric, and oil-related faults [1]. The need for better dielectrics and transformer oils for insulation is unequivocal. In a liquid-filter transformer, the insulator liquid plays an important function by providing both the electrical insulation and the means of transforming the thermal losses to the cooling system. Insulating oil in a transformer must ensure the transfer of heat. This function is realized both by thermal conductivity and convection [2].

Nowadays, transformers can be filled with three basic types of insulating liquids: (i) mineral oils, (ii) synthetic oils or (iii) natural esters [3]. The use of each type is fortified by the application. However, in the face of increasing demand for the use of environmentally friendly products in the industry, more and more companies are working towards developing the use of esters and specifically natural esters for use in the majority of their products.

Transformers have been filled with mineral oil for more than one century. This type of oil is a petroleum based product, essentially composed of hydrogen and carbon atoms. Carbon and hydrogen are assembled in different structures: napthenic (C_nH_2n), paraffinic (C_nH_2n+2) and

aromatic (C_nH_2n-6)[3]. The distribution of carbons in napthenic and paraffinic structures define

the type of mineral oil. This distribution is controlled by the crude oil and the refining processes used. Because of its wide availability, good properties and low cost, mineral oil is the fluid most used in the electric power transformer industry. New mineral oils have to be in accordance with the IEC 60296 or ASTM D3487. As mineral oil has been used for such a long time, a large data....

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