Design And Construct A Single Phase Auto-Transformer Of Rating 3Kva, And Step Down Voltage Of 240V And Voltage Taps Of 120, 48, 24V, 12V.

The project presents here is on design and construct a single phase auto-transformer of rating 3kva, and step down voltage of  240v and voltage taps of 120, 48, 24v, 12v.

An autotransformer is an electrical transformer with only one winding. In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps where electrical connections are made. Autotransformers have the advantages of often being smaller, lighter, and cheaper than typical dual-winding transformers, but autotransformers have the disadvantage of not providing electrical isolation.

The ain of this work is to build a 3kw autotransformer with step down voltage of  240v and voltage taps of 120, 48, 24v, 12v.

TABLE OF CONTENT

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

1.0      INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

1.2      PROBLEM STATEMENT

1.3      AIM OF THE PROJECT

1.4      SIGNIFICANCE OF THE PROJECT

1.5      LIMITATION/PROBLEM OF THE PROJECT

1.6      APPLICATION OF THE PROJECT

1.7      PURPOSE OF THE PROJECT

CHAPTER TWO

2.0      LITERATURE REVIEW

2.1      REVIEW OF TRANSFORMER HISTORY

2.2      REVIEW OF TYPES OF TRANSFORMER

2.3      REVIEW OF CLASSIFICATION OF TRANSFORMER

2.4      REVIEW OF IMPORTANCE OF DIFFERENT KINDS OF TRANSFORMER COOLING SYSTEM

2.5      REVIEW OF MAINTENANCE OF TRANSFORMER COOLING SYSTEM

CHAPTER THREE

3.0      CONSTRUCTIONS

3.1      AUTOTRANSFORMER BASICS

3.2      OPERATION OF AUTOTRANSFORMER

3.3      AUTOTRANSFORMER DESIGN

3.4      AUTOTRANSFORMER CONSTRUCTION

3.5      DESIGN CALCULATION

CHAPTER FOUR

4.0      RESULT ANALYSIS

4.1      ASSEMBLING OF SECTION AND TESTING

4.2      TESTING OF SYSTEM OPERATION

4.3      PROBLEMS ENCOUNTERED

5.4      COST ANALYSIS

CHAPTER FIVE

5.1      CONCLUSION

5.2      RECOMMENDATION

5.3      BIBLIOGRAPHY

CHAPTER ONE

1.0                                                      INTRODUCTION

In an autotransformer, portions of the same winding act as both the primary and secondary sides of the transformer. The winding has at least three taps where electrical connections are made. Autotransformers have the advantages of often being smaller, lighter, and cheaper than typical dual-winding transformers, but autotransformers have the disadvantage of not providing electrical isolation.

The aim of this project is to build a step down voltage of 240v as the primary voltage and 120, 48, 24v, 12v was designed.

1.2                                               PROBLEM STATEMENT

multiple-winding transformers are always require much copper winding, for this reason they are always heavy, expensive and bulky. To overcome this problem an auto-transformer was invented. Autotransformer uses fewer windings and a smaller core, an autotransformer for power applications is typically lighter and less costly than a two-winding transformer, up to a voltage ratio of about 3:1; beyond that range, a two-winding transformer is usually more economical.

In three phase power transmission applications, autotransformers have the limitations of not suppressing harmonic currents and as acting as another source of ground fault currents. A large three-phase autotransformer may have a “buried” delta winding, not connected to the outside of the tank, to absorb some harmonic currents.

In practice, losses mean that both standard transformers and autotransformers are not perfectly reversible; one designed for stepping down a voltage will deliver slightly less voltage than required if it is used to step up. The difference is usually slight enough to allow reversal where the actual voltage level is not critical.

autotransformers use time-varying magnetic fields to transfer power. They require alternating currents to operate properly and will not function on direct current.

1.3                                          AIM OF THE PROJECT

The aim of this work is to build a 240v autotransformer with step down voltage of 240v/120, 48, 24v, 12v.

1.4                                           PURPOSE OF THE PROJECT

The purpose of this work is to construct a transformer with only one winding wound on a laminated core. In auto transformer, the primary and secondary winding are interrelated. A part of the winding is common to both primary and secondary sides. On load condition, a part of the load current is obtained directly from the supply and the remaining part is obtained by transformer action

1.5                              SIGNIFICANCE OF THE PROJECT

1. The auto transformer can increase the voltage a bit. The auto transformer can also decrease the voltage by a bit if that is what is needed.
2. For transformation ratio = 2, the size of the auto transformer would be approximately 50% of the corresponding size of two winding transformer. For transformation ratio say 20 however the size would be 95 %. The saving in cost of the material is of course not in the same proportion. The saving of cost is appreciable when the ratio of transformer is low, that is lower than 2. Thus auto transformer is smaller in size and cheaper.

iii. An auto transformer has higher efficiency than two winding transformer. This is because of less ohmic loss and core loss due to reduction of transformer material.

1. Auto transformer has better voltage regulation as voltage drop in resistance and reactance of the single winding is less.

1.6                              LIMITATION OF THE PROJECT

An autotransformer does not provide electrical isolation between its windings as an ordinary transformer does; if the neutral side of the input is not at ground voltage, the neutral side of the output will not be either. A failure of the insulation of the windings of an autotransformer can result in full input voltage applied to the output. Also, a break in the part of the winding that is used as both primary and secondary will result in the transformer acting as an inductor in series with the load (which under light load conditions may result in near full input voltage being applied to the output). These are important safety considerations when deciding to use an autotransformer in a given application.

1.7                  APPLICATIONS OF AUTOTRANSFORMER

1. Compensating voltage drops by boosting supply voltage in distribution systems.
2. Auto transformers with a number of tapping are used for starting induction and synchronous motors.

Auto transformer is used as variac in laboratory or where continuous variable over broad ranges are required.