DESIGN AND CONSTRUCTION OF A 60AMP THREE PHASE AUTOMATIC CHANGEOVER SWITCH

ABSTRACT

The design and construction of a 60A, 3-Ф automatic power changeover from public utility supply to generator and vice versa was aimed at providing a useful system for use in our homes or offices. The system was achieved with a 66A 3-Ф contactor, 100mA transformers and relays. The system turns on a generator when the public utility (PHCN) is off by cranking the starter and a provision was made to stop cranking when the generator is fully started. A delay was provided to stop the generator five minutes after the PHCN is restored to avoid unnecessary off and on. A display that shows when PHCN or GEN is on was provided.

TABLE OF CONTENT

COVER PAGE……………………………………………………………i

TITLE PAGE …………………………………………………………..…ii

APPROVAL PAGE…………………………………… …………………iii

DEDICATION …………………………………………………………….iv

ACKNOWLEDGEMEN ………………………………………………. …v

ABSTRACT………………………………………………………………..vi

TABLE OF CONTENTS…………………………………………………..vii

CHAPTER ONE: INTRODUCTION………………………1

1.1 BACKGROUND OF STUDY……………………………………………1

1.2 AIMS AND OBJECTIVE………………………………………………..2

1.3 RELEVANCE OF THE STUDY…………………………………………3

1.4 SCOPE OF THE PROJECT………………………………………………4

1.5 STATEMENT OF THE PROBLEM………………………………………5

1.6 IMPORTANCE OF THE STUDY…………………………………………7 viii

1.7 PROJECT REPORT ORGANIZATION…………………………8

CHAPTER TWO: LITERARTURE REVIEW…………………..……………9

2.1 HISTORICAL BACKGROUND…………………………………….9

2.2 DISCRIPTION OF COMPONENTS USED ………………………………13

2.3 CONTACTOR………………………………………………………… …13

2.3.1 OPERATING PRINCIPLES………………….………………………….15

2.3.2 APPLICATIONS…………………………………….……………………17

2.4 RESISTORS………………………………………………………………..18

2.4.1a USES OF RESISTORS………………………………………………….19

2.4.1b TYPES OF RESISTORS………………………………………………19

2.4.1c FIXED RESISTORS……………………………………………………20

2.4.1d VARIABLE RESISTORS………………………………………………20

2.5 CHARACTERISTICS OF RESISTORS…………………………………….21

2.6 CAPACITORS……………………………………………………………….21

2.6a TYPES OF CAPACITORS ………………………………………22 ix

2.6b USES AND APPLICATION OF CAPACITORS…………………………..22

2.7 TRANSFORMERS……………………………………………………………23

2.7a USES OF TRANSFORMER…………………………………………………25

2.8 RELAYS………………………………………………………………………25

2.8a TYPES OF RELAYS………………………………………………………..26

2.8b FACTORS TO CONSIDER BEFORE SELECTING A RELAY…………..27

2.8c APPLICATION OF RELAY………………………………………………..28.

2.9 DIODES………………………………………………………………………28

2.9a USES OF DIODES………………………………………………………….29

2.10 CRYSTAL OSCILLATORS………………….………………………………29

2.10a TYPES OF CRYSTAL OSCILLATORS……………………………………29

2.10b TERMS ASSOCITED WITH CRYSTAL OSICLLATORS……………….30

2.1Oc APPLICATION AND USES OFF CRYSTAL OSCILLATORS…………31

2.11 REGULATORS………………………………………………………………31

2.11a APPLICATION AND USES OF REGULATOR……………………….…32 x

2.12 TRANSISTORS……………………………………………………………..32

2.12a TYPES OF TRANSISTORS……………………………………………….33

2.12b USES OF TRANSISTORS…………………………………………………33

2.13 PROGRAMMABLE INTERFACE CONTROLLER (PIC)………………..34

2.14 SEVEN SEGMENT DISPLAY (SSD)………………………………………35

CHAPTER THREE: SYSTEM OPERATION……………….………………..37

3.1 BLOCK DIAGRAM AND OPERATION……………………………………37

3.2 CIRCUIT DIAGRAM AND OPERATION………………………………….44

CHAPTER FOUR: CIRCUIT DESIGN AND OPERATION………………….48

4.0 CIRCUIT DESIGN AND OPERATION………….………………………….48

4.1 CHOICE OF CONTACTOR………………………………………………….48

4.2 CHOICE OF TRANSFORMER………………………………………………48

4.3 CALCULATION FOR RECTIFICATION……………………………………49

4.4 GENERATOR TURNOFF DELAY…………………………………………..50

4.5 COMPLETE DESIGNED CIRCUIT OF THE DISPLAY AND CONTROL……………………………51 xi

4.6 CALCULATION FOR THE SEVEN SEGMENT TRANSISTOR SWITCHING……………………55

4.7 CURRENT DEMAND FOR THE DISPLAY UNIT…………………………55

4.8 DISPLAY PROGRAM SOURCE CODE………….…………………………56

CHAPTER FIVE

5.1 TESTING, RESULT AND PROJECT COSTS………………………………60

5.2 TESTING……………………………………………………………………..60

5.2a VOLTAGE TESTS…………………………………………………………..60

5.2b RESISTANCE TESTS………………………………………………………61

5.2C OPERATION TESTS……………………………………………………….63

CHAPTER SIX

6.1 CONCLUSION……………………………………………………………..67

6.2 RECOMMEDATION……………………………………………………….70

REFRENCES…………………………………………………………………….71 xii

LIST OF FIGURES

Figures pages

Contactor symbol…………………………………………………………….. 15

Symbol of a fixed resistor ……………………………………………………..20

Symbol of a variable resistor …………………………………………………..21

Symbol of a capacitor ………………………………………………………….22

Transformer and its winding …………………………………………………..24

Symbol of a relay ……………………………………………………………….26

Diode symbol …………………………………………………………………..28

Oscillator ……………………………………………………………………….29

Regulator ……………………………………………………………………….32

Pic (16f8676A) …………………………………………………………………34

Seven segment symbol …………………………………………………………35

555 timer symbol ………………………………………………………………36

Block diagram …………………………………………………………………37 xiii

Circuit diagram ……………………………………………………………….43

System display flowchart ……………………………………………………..46

Step down transformer rating (windings) …………………………..……… .48

Rectification circuitry………………………………………………………… 49

Delay circuitry …………………………………………… …………… …….50

Seven segment display and controller circuitry………………….53

Display/transistor switching circuitry……54

LIST OF TABLES

TABLES pages

Summary of performance evaluation…… 40

Project cost /BEME (bill of engineering measurement and evaluation)…………65

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