Design And Construction Of A Digital Changeover Switch With Generator Shutdown Feactures

ABSTRACT

The Changeover Switch is a device used to switch off a power supply and subsequently switch on another power supply. Basically it is aimed at switching on a more convenient power supply to the load. The aim of this work is to build a digital Changeover Switch that switches OFF the generator and automatically changes over to mains grid when mains grid power is restored. A digital Changeover Switch will automatically switch OFF your generator and change over to MAIN ( Public power supply/PHCN) on power resumption.

This was achieved  by the use of electrical components such as microcontroller, resistors, capacitors, diodes, transistors, opto-isolators etc., The microcontroller unit circuit is the heart of the project. This is where; the program for the control part of the project is written and burned using assembly language and a universal programmer, respectively.  Due to the looping of the pole of the contactor to give 50A  current each for PHCN and generator, the maximum power the circuit can withstand on an a.c voltage of 240V is 12KVA. This means the circuit can carry a large amount of power in homes and offices.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• PROBLEM STATEMENT
• AIM OF THE PROJECT
• PURPOSE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• BENEFIT OF THE PROJECT
• APPLICATION OF THE PROJECT
• METHODOLOGY
• DEFINITION OF TERMS
• PROJECT ORGANISATION

CHAPTER TWO

LITERATURE REVIEW

• REVIEW OF RELATED LITERATURE
• MANUALLY CONTROLLED CHANGE-OVER
• LIMITATIONS OF MANUAL CHANGEOVER SYSTEM
• SEQUENTIAL LOGIC-CONTROLLED CHANGEOVER (SLC)
• MICROPROCESSOR-BASED CONTROL
• DESCRIPTION OF THE NEW SYSTEM
• RELATED COMPONENTS IN THE SYSTEM DESIGN

CHAPTER THREE

3.0      METHODOLOGY

• SYSTEM BLOCK DIAGRAM
• IMPLEMENTATION OF THE MICROCONTROLLER SYSTEM
• IMPLEMENTATION OF THE MODE SELECT SWITCH
• IMPLEMENTATION OF FEEDBACK OR VOLTAGE MONITOR CIRCUIT
• IMPLEMENTATION OF CHANGEOVER SWITCH
• IMPLEMENTATION OF CONTROL LOGIC
• THE KICK STARTER FOLLOWS THIS ALGORITHM
• CHANGEOVER CONTROL ALGORITHM
• MICROCONTROLLER UNIT
• DESCRITION OF AN AT85s52 MICROPROCESSOR

CHAPTER FOUR

4.0    IMPLEMENTATION AND TESTING

• SOFTWARE IMPLEMENTATION
• BREADBOARDING AND VEROBOARDING ASSEMBLY
• METHOD OF TESTING
• CASING AND PACKAGING
• ACHIEVEMENTS
• RESULTS AND DISCUSSIONS

CHAPTER FIVE

• CONCLUSION
• PROBLEMS ENCOUNTERED
• RECOMMENDATION
• REFERENCES

CHAPTER ONE

1.0                                          INTRODUCTION

1.1                            BACKGROUND OF THE STUDY

The need for constant and stable power supply in a country, state or city cannot be overemphasized. In most developing nations, industries, firms and organizations contest for power supply that is unreliable and insecure, thus marring the effect of productivity and development. In these nations, the quest for secure and reliable power supply remains a dream yet to be achieved. This is as a result of increase in population, industrialization, urbanization (Aguinaga, 2008; Fuller, 2007; Kolo, 2007) and lack of proper planning by the government and utility providers. Most manufacturing industries, firms and institutions such as hospitals and healthcare facilities, financial institutions, data centers and airports to mention, but a few require constant power supply throughout the year. Volatility in power generally delays development in public and private section of any economy (Kolo, 2007; Anon, 2010; Chukwubuikem, 2012). For instance, power failure could lead to prohibitive consequences ranging from loss of huge amounts of money to life casualties (Aguinaga, 2008). This instability in power supply has led to the development of switching systems between national grid power system and standby generators used as backup. In the past decade, various equipment and configurations have been put in place in order to manage this problem (Aguinaga, 2008). An automatic changeover switching system makes use of contactors, active and passive components and transducers to realize changeover in a shorter time while excluding human interference and its attendant (Chukwubuikem, 2012). The research project is designed for power supply applications. It involves automatic change over between the mains power supply and a standby generating set. The project implements an automatic switching or starting of the power generator, whenever the main power fails. The circuit of the project consists of logical control units, display units, alarm units and relay switches. The design of the project takes into consideration practical or real life situations and a lot of precautions were put in place to make its performance acceptable, even though it is a prototype design. The basic operation of the project is to switch ON an auxiliary power supply (a generator). This operation connects the power supply from the generator to the load after a predetermined time interval. This is intended to normalize the current from the generator. Switching is possible through the use of the relays. The system was designed to automatically change power supply back to the main supply moments, after the A.C. mains are restored and to switch OFF the generator.

1.2                                   PROBLEM STATEMENT

Power failure or outage in a country, state or city is highly detrimental to development in public and private industries. The insecurity associated with constant or frequent power failure or outage brings about limitation to power  consistent investments, thus hampering the development of industries and multinational ventures. Processes like carrying out surgical operations in hospitals, laboratories which require constant power supply for research, money transactions  between banks and more require constant use of uninterrupted power. In other to solve this problem, an automatic changeover switch was invented. This research covers the design and construction of a single phase digital automatic power changeover. It has the capacity to automatically switch power from  national grid to generator and vice versa, once there is power failure in any of the two power supplies and at the same time has the capacity of shutting down a generator set once the mains grid is been restored.

1.3                                    AIM OF THE PROJECT

The main aim of any electric power supply in the world is to provide uninterrupted power supply at all times to all its consumers. Although, in developing countries such as Nigeria, the electric power generated to meet the demands of the growing consumers of electricity is insufficient, hence power instability and outage becomes the order of the day.

In view of these considerations, this project is aimed at building a workable digital changeover switch which switches ON power from power Holding Company (PHCN) to a generator when power fails and from generator to PHC when power comes back and then shut down the generator automatically.

1.4                               PURPOSE OF THE PROJECT

The main purpose of this work is to provide a means of having uninterruptible power supply in our home, office, workshops or industries.

1.5                          SIGNIFICANCE OF THE PROJECT

The automatic change over switch, the switch aimed at achieving the following automatic actions;

• To change power over to generator
• To change back to PHCN
• To change the generator.
• Display the status of the device via LCD

The automatic change over switch has the following advantages;

It minimizes damages to lives/equipment since it has its own monitoring system and its switching requires no human contact with the switch, thus eliminating human error.

It reduces its changeover timing to the minimum due to its fast response to power outage.

It maintains high quality of service through its fast and prompt response.

Moreover, the size and captivity of the unit will depend upon the load for which it will be used. The unit is also portable, easy, convenient and safe to install.

1.6                             BENEFIT OF THE PROJECT

In every home, office or industries, automatic power changeover  plays a vital role, that is, It provides a means of switching from utility AC mains to generator in the case of power failure; This project has been improved on the existing types of electromechanical device that has being in use over the years.

1.7                         LIMITATION OF THE PROJECT

This work covers only a one phase automatic changeover which can only be used for providing a means of switching from one phase of AC mains to generator set in the case of failure in public utility.

1.8                           APPLICATION OF THE PROJECT

This device is used in the following places:

1. home,
2. office,
3. worship places
4. workshops or industries

1.9                                         METHODOLOGY

To achieve the aim and objectives of this work, the following are the steps involved:

1. Study of the previous work on the project so as to improve it efficiency.
2. Draw a block diagram.

• Test for continuity of components and devices,

1. programming of microcontroller
2. Design and calculation for the changeover was carried out.
3. Studying of various component used in circuit.

• Construct a digital changeover circuit.
• Finally, the whole device was cased and final test was carried out.

1.10                                           DEFINITION OF TERMS

POWER OUTAGE / POWER FAILURE: A power outage is the loss of the electrical power network supply to an end user.

AUTOMATIC CHANGEOVER is device that automatically transfers power from generator supply to PHCN supply when available and stops the generator without without human intervention

1.11                                           PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work,   chapter two presents the literature review of the study,  chapter three describes the methods applied,  chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.