Power Transformer Winding Thermal Analysis Considering Load Condition And Type Of Oil

ABSTRACT

Power transformer outages have a considerable economic impact on the operation of an electrical network. In order to draw maximum power from transformers and, at the same time, avoid thermal mishaps, it is essential to carefully study its thermal behavior. Furthermore, an accurate computation of the hottest spot temperature (HST) helps in a realistic estimation of the reliability and remaining life of the transformer winding insulation. This paper presents steady state temperature distribution of a power transformer layer-type winding using conjugated heat transfer analysis, therefore energy and Navier-Stokes equations are solved using finite difference method. Meanwhile, the effects of load conditions and type of oil are investigated using the model. Oil in the transformer is assumed nearly incompressible and oil parameters such as thermal conductivity, special heat, viscosity, and density vary with temperature. Comparing the results with those obtained from finite integral transform checks the validity and accuracy of the proposed method.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

1.1   INTRODUCTION

1.2   OBJECTIVE OF THE STUDY

1.3   SCOPE OF THE STUDY

CHAPTER TWO

LITERATURE REVIEW

2.1   REVIEW OF  DIFFERENCE BETWEEN POWER TRANSFORMER AND DISTRIBUTION TRANSFORMER

2.2    REVIIEW INSULATING OIL

2.3   TYPES OF TRANSFORMER OIL

2.4    PROPERTIES OF TRANSFORMER INSULATING OIL

2.5    CHEMICAL PARAMETERS OF TRANSFORMER OIL

2.6    PHYSICAL PARAMETERS OF TRANSFORMER OIL

CHAPTER THREE

METHODOLOGY

3.1      POWER TRANSFORMER CONSTRUCTION – WINDINGS

3.2      TRANSFORMER CONSTRUCTION OF THE CORE

3.3      POWER TRANSFORMER CORE CONSTRUCTION

3.4      TRANSFORMER LAMINATIONS

3.5    TRANSFORMER CORE TYPES

3.6     TRANSFORMER WINDING ARRANGEMENTS

3.7     TRANSFORMER CORE LOSSES

CHAPTER FOUR

TEMPERATURE RISE TEST OF TRANSFORMER

4.1      TEMPERATURE RISE TEST FOR TOP OIL OF TRANSFORMER

4.2      WINDING TEMPERATURE RISE TEST ON TRANSFORMER

CHAPTER FIVE

• CONCLUSION
• REFERENCES

 CHAPTER ONE

1.1                                                        INTRODUCTION

In a power transformer, a part of the electrical energy is converted into the heat. Although this part is quite small comparing to total electric power transferred through a transformer, it causes significant temperature rise, which represents the limiting criteria for possible power transfer through a transformer. That is why the precise calculation of temperatures in critical points (top oil and the hottest solid insulation spot) is of practical interest. Thermal impact leads not only to long-term oil/paper-insulation degradation; it is also a limiting factor for the transformer operation. Therefore, the knowledge of the temperature, especially the hottest spot temperature, is of high interest.  If the temperature rise goes beyond the permissible value, the load of transformer must be reduced or an auxiliary transformer is used in order to preserve the insulation from deterioration. For an oil-immersed transformer, the oil surrounds the transformer body. Oil is a nearly incompressible fluid and density changes due to temperature rise, therefore oil moves in the transformer. The heat transferred by convection is the most important method of heat transfer.

Hottest spot temperature must not exceed the prescribed value in order to avoid insulation faults. A hottest spot temperature calculation is given in the International Standards. The algorithm for calculating the hottest spot temperature of a directly loaded transformer using data obtained in a short circuit heating test.  Heat transfer theory results from winding to oil.

In this paper, author has proposed a procedure for obtaining the temperature distribution in the power transformer and the effects of load conditions and type of oil are investigated using the model.  For this reason energy and Navier-Stokes equations are solved using finite difference method. The model can be used for temperature calculation on the arbitrary change of current and outside air temperature.

1.2                                               OBJECTIVE OF THE STUDY

The objective of this paper is to presents steady state temperature distribution of a power transformer layer-type winding using conjugated heat transfer analysis, therefore energy and Navier-Stokes equations are solved using finite difference method. Meanwhile, the effects of load conditions and type of oil on HST are investigated using the model.

1.3                                    SCOPE OF THE STUDY

Thermal impact leads not only to long-term oil degradation; it is also a limiting factor for the transformer operation.Therefore, the knowledge of the temperature, especially the hottest spot temperature, is of high interest. If the temperature rise goes beyond the permissible value, in order to preserve the insulation from deterioration, the load of transformer must be reduced or an auxiliary transformer is used. For an oil-immersed transformer, the oil surrounds the transformer body. Oil is a nearly incompressible fluid and density changes due to temperature rise, therefore oil moves in the transformer. The heat transferred by convection is the most important method of heat transfer. The analytical solution of convection equation is normally difficult and sometimes it is impossible due to the complexity of the geometry.