Design And Construction Of An Intelligent Change Over Switch For A Three Phase Supply

ABSTRACT

This work is on an intelligent change over for a three phase supply. The system uses phase sensors to monitor the voltage in each phase. The voltages monitored by the phase sensors are then fed into the analog to digital converters (ADCs) embedded inside the PIC microcontroller for analysis. The PIC microcontroller is in charge of all the control operation in the system and takes intelligent decisions based on the analysis. The decisions of the microcontroller are used to control the operation of the power circuit, which has three contactors, through relays. The phase sensors also help the system to sense any abnormal condition in any of the phases which may be low voltages, high voltages or blackouts. The system automatically disconnects the load from the mains source when there is any abnormality and transfers it to the standby generator source. It then starts the standby generator and continues to monitor the mains for the restoration of power. Once power is restored and the quality of power in the phases is perfect, the system automatically transfers the load to the mains source and stops the standby generator. At each point in time, the voltage levels of each of the phases of both the mains and the generator outputs are displayed on the 16 by 4 line LCD display.

TABLE OF CONTENTS

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• BACKGROUND OF THE STUDY
• PROBLEM STATEMENT
• AIM/OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• LIMITATION OF THE PROJECT
• PURPOSE OF THE PROJECT
• APPLICATION OF THE PROJECT
• DEFINITION OF TERMS
• METHODOLOGY
• PROJECT ORGANISATION

CHAPTER TWO

2.0     LITERATURE REVIEW
2.1     REVIEW OF ELECTRICAL PHASES
2.2     REVIEW OF THREE-PHASE ELECTRIC POWER
2.3     REVIEW OF THREE PHASE GENERATION AND DISTRIBUTION
2.4   REVIEW OF THREE-PHASE LOADS

2.5      OVERVIEW OF RELEVANT TECHNOLOGY

2.6      REVIEW OF RELATED WORKS EXISTING SYSTEM

2.7      SUMMARY OF REVIEWED WORKS

CHAPTER THREE

3.0      METHODOLOGY

3.1     INTRODUCTION

3.2     SYSTEM BLOCK DIAGRAM

3.3     BLOCK DIAGRAM DESCRIPTION

3.4      SYSTEM POWER SUPPLY

3.5      VOLTAGE MONITORING

3.6     THE CONTROL SYSTEM USING PIC MICROCONTROLLER

3.7      PHASE SELECTOR AND MONITORING

CHAPTER FOUR

4.0      TESTING, OPERATION AND RESULT

4.1      SYSTEM TESTING

4.2      BASIC OPERATION OF THE SYSTEM

4.3      RESULT AND DISCUSSION

4.4      CASING AND PACKAGING

4.5      DIMENSION OF THE CASING

4.6      ECONOMIC OF THE PROJECT

4.7      PROJECT VIABILITY

4.8      RELIABILITY

CHAPTER FIVE

5.0      SUMMARY, CONCLUSION AND RECOMMENDATION

5.1      SUMMARY

5.2      CONCLUSION

5.3      RECOMMENDATION

REFERENCES

CHAPTER ONE

1.0                                             INTRODUCTION

1.1                                     BACKGROUND OF THE PROJECT

The unstable power supply in Nigeria has been an issue of great concern to the dwellers [1]. This retards development as well as negatively affects other realms of life in general. As a measure to overcome this, the use of generator has been adopted by the general masses. At the time of the power failure, manual change over from mains to generator imposes a lot of challenges which needs solution [1]. These challenges include the physical need for the presence of a person for switching on and off the generator with the accrued inconveniences of staying awake, phone calls or climbing down and up the stairs to start or off the generator.

Other challenges include cost in running of the generator not knowing that power has been restored and the risk of electric shock. Different technologies have, however, been designed and implemented for the purpose of overcoming the above listed challenges. Unfortunately, these technologies still pose different short comings which still need solution. The design and implementation of a 3-Phase Intelligent Changeover System aim at overcoming the above limitations as well as adding other necessary features.

1. Changeover

A changeover switch is a system like relay which could be manually or automatically operated, that can be used to supply power to a load or cut the power off. Also, contactors can be combined and used to change one source of power supply to another source in case of failure from either of the two sources. It is particularly necessary when using more than one source of electricity supply. In this write up, the changeover is not only automatic but intelligent.

1. Generator Compatibility to the System

The automatic change-over switch can be used in any place where alternative power is needed to complement the main power supply. In this project, a generating set is used as an alternative power supply. Thus, the following are important.

The generator must have soft touch ‘start and stop’ facility. (b) The generator’s battery has to be in good condition always and good alternator. (c) The inter- connecting cables must be in good order.

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.

1.4                                              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                          AIM AND OBJECTIVE OF THE PROJECT

The main aim of this work is to design a device that will overcome power interruption by automatically switching power from national grid to generator and vice versa. The objectives are:

1. To have a reliable and uninterruptible power supply
2. To build a an automatic changeover switch with automatic generator start and stop

• To reduce human labour

1.6                                      SIGNIFICANCE OF THE PROJECT

Industries require three phases power to run their machinery. Some of them require continuous \ uninterrupted power to maintain their data.

Auto three phase power changeover introduces an automatic solution to overcome power interruption by automatically switching power from  national grid to generator and vice versa

This automatic change over unit operates in three phase system. 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 change over 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.

1.4                                        LIMITATION OF THE PROJECT

In the course of designing this project, different kinds of problem was notice such as:

• Difficulty in troubleshooting with circuit without the circuit diagram
• Difficulty in connecting the output without the three phases short-circuiting, until a multiplexing circuit was gotten.
• Difficult in wiring because of the strong wiring the project required.
• This automatic change over unit operates in three phase system.

1.5                                                SCOPE OF THE STUDY

This work covers only a three phase automatic changeover which can only be used for providing a means of switching from generator to utility supply in the case of failure in the three phase. The system uses phase sensors to monitor the voltage in each phase. The voltages monitored by the phase sensors are then fed into the analog to digital converters (ADCs) embedded inside the PIC microcontroller for analysis. The system has with automatic generator start and stop control.

1.6                                          APPLICATION OF THE PROJECT

This device is used in the following places:

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

1.7                                                        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. Design and calculation for the changeover was carried out.
2. Studying of various component used in circuit.
3. Construct a digital changeover circuit.

• Finally, the whole device was cased and final test was carried out.

1.8                                                         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 human intervention

1.8                                                         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.