Voltage stabilizers are used for many appliances in homes, offices and industries. The mains supply suffers from large voltage drops due to losses on the distribution lines en route. A voltage stabilizer maintains the voltage to the appliance at the nominal value of around 220 volts even if the input main fluctuates over a wide range.
In this work, an automatic voltage stabilizer that can be adapted to any power rating. Its intelligence lays in the program on PIC 16F873A —a low-cost microcontroller that is readily available. The circuit, when used with any appliance, will maintain the voltage at around 220V even if the input mains voltage varies between 90V and 240V.
This acts within 100ms to produce a smoothly varying output whenever input mains voltage changes. (Servo stabilizers move a variable contact on a toroidal auto transformer to adjust the output when input goes up and down, which takes seconds.)
The PIC16F877A is an RISC (reduced instruction set computer) microcontroller with 35 instructions, and hence program development with it is rather tough. But, there are good support programs.

TABLE OF CONTENTS
Cover Page
Title Page
Approval Page
Dedication
Acknowledgment
Abstract
Table of Contents

CHAPTER ONE
1.0      Introduction
1.1      Background of the project
1.2      Aim/objective of the project
1.3      Significance of the project
1.4      Scope of the project
1.5      Limitation of the project
CHAPTER TWO
2.0      Literature Review

• Historical background of the project
• Stages in the development of voltage stabilizer
• Stabilizer grading
• Types of stabilizer

CHAPTER THREE
3.0      construction methodology

• Block diagram
• Circuit diagram
• Circuit description
• System operation
• Description of major components used
• Theory of transistor
• Theory of capacitors
• Theory of op-amp
• Theory of zener diode
• Theory of transformer
• Theory of resistors
• Cost analysis

CHAPTER FOUR
4.0      Result analysis

• Construction procedure
•  Casing and packaging
• Assembling section
• System testing
• Design precaution

CHAPTER FIVE

• Discussion, Conclusion and Recommendation

5.1      Discussion

• Conclusion
• Recommendation
• References

CHAPTER ONE
1.0                                                     INTRODUCTION
In Nigeria and some other parts of the world today, the electricity power supply to consumers (at homes and industries) are not maintained at a stipulated voltage say 240 volts.  But the electronics gadgets and some other power operated machines, that we use in our homes, offices and industries requires power with constant or nearly constant voltage for their efficiency, and to avoid damage by the voltage.
Voltage stabilizer is an electronic control circuit or device that is capable of providing a constant or nearly constant output voltage even when there is variation in load or input voltage as low as 90 volt can be boast up to 240 volt by stabilizer at output stage without any voltage fluctuation.

1.1 BACKGROUND OF THE PROJECT

There are many fundamental different types of stabilizers in use some of which are electron mechanically tap changer, solid state tap changer etc. voltage, stabilizer came into being not by normal design and plain, but as a means of solving electrical “Crisis” situation.  This crisis situation does rarely occur in developed countries of the world such as Britain, American, Germany.

Their system of generation, transmission and distribution of electricity is such that a devoid of variation of fluctuation in  the supplied voltage.  Now, by the definition given by K.G Jackson and R. Feinberg, a voltage stabilizer is a piece device incorporated in a circuit to maintain a constant output voltage from a poorly generated power supply.  A voltage stabilizer like any other piece of equipment is a combination of many electrical and like any other piece of equipment is a combination of many electrical and electronic and circuit with the aim of getting the assemble to perform a specified desired task or function.

1.2 OBJECTIVE OF THE PROJECT

The objective of this work is to construct a device whose function is to maintain constant voltage and power line conditioning to the equipment load under a wide variety of conditions, even when the utility input voltage, frequency or system load vary widely. The AVR shall consist of an all copper, multiple tapped, triple shielded isolation transformer and contain independently controlled inverse parallel electronic switches for each of the 7 taps per phase to provide tight voltage regulation. The phase current shall be monitored for zero current recognition to initiate any required tap change. Linear devices shall be used for line synchronization to prevent phase shift errors normally associated with simple CT zero current crossing acquisition. The system shall be microprocessor controlled.

1.3 SIGNIFICANCE OF THE PROJECT

The Automatic voltage regulator is a voltage regulator planned to mechanically sustain a constant voltage level. It is very device to maintain a constant voltage level. It can also use electromechanical components. It can be used majorly to regulate one or more DC or AC depending on the design. Therefore, the functions of this equipment are very wide and can be used majorly for various purposes. Electronic voltage regulators can be used majorly for various purposes. It has various functions like it can be used mainly for stabilizing the DC voltages that can be used by the processor and its main parts. In central power station generator plants and automobile alternators, voltage regulators control the output of the plant. In this distribution system, it may be installed at along distribution lines so that all clients recognize steady voltage self-regulating of how much power is drawn from the line. There are many functions of operating the AC depending upon the design. It is very good option to maintain the constant voltage level. Automatic voltage regulator is a superb invention of science, which is an electric device designed to authorize a constant voltage in a settable level. It is very helpful to maintain the preferred voltage for the generators within particular limits. The main working of it depends upon the laws of electromechanical physics. It consists of numerous vigorous and unreceptive electrical parts like thermostats, adopters and diodes. Apart from this, there are many reliable Automotive Suppliers in India that produce many kinds of equipments like generator, regulator and other major parts. They are well known for various kinds of functions and various specifications. They not only produce higher quality products, but also they will provide some additional benefits with the parts of these equipments. Auto Voltage Regulator Generator is the most important part for great amplifier to work. Its types are many, but they are highly in functionality and better performance. They are well equipped with self functioning controls and starts up functions which make them very easy and useful to handle easily and completely. They have different sizes, shapes and colors. There are also automatic regulators which are so small that they can be easily places on a small printed circuit board. They are very easy and portable to handle. They may cover a higher volume of small house sometimes. Therefore, there is a wide variety in the automatic voltage regulators and each has its own specifications.

1.4                                         THE SCOPE OF THE PROJECT
The design and construction of an Automatic Voltage Regulator is the project we are construction.  We are working on this machine because we have some idea on how this machine can be constructed and also on how it works.  We are also doing this because we want to learn more about it.
As we have mentioned earlier, this device is a protective device that protects our electrical and electronic appliances out of current and voltage fluctuation. This is how it works.  When this system is plugged into the socket or supply, it will receive a minimum voltage of 100v and filter the current and voltage thereby brings out suitable voltage output to be used by the devices in it.
So, we are building or constructing this device to reduce risk and damages the fluctuation of current / voltage caused by power fluctuations.  Before building this device, the following points and specifications should be kept in mind so that the device we build can work properly and give us the desired results:

• The range of input voltage should be 90 to 260V.
• The range of output voltage should be 200V to 240V.
• There should be no change in the waveform or the frequency of input/output voltages.
• The material used in it should not be too much expensive otherwise there would be no use of making it at home by going through all the trouble, can just buy a cheap one from market instead. Therefore it should not be expensive.
• No varistors or variable resistors should be present in the final form of the product.
• A total of 4 relays are used in the circuit.
• The auto transformer used has 4 additional tappings set at 165V, 190V, 215V and 240V, all with a difference of about 25V.
• The microcontroller used is PIC 16F873A.

1.5                                        LIMITATION OF THE PROJECT

The system design shall be capable of operating at an input frequency range of -15% to +10% of nominal, without clearing protective devices or causing component failure within the AVR. When generator or utility power is restored, the AVR shall automatically restart. Upon turn on or restart, the output of the AVR shall not exceed the specified output regulation limits.
If the input voltage or frequency exceeds programmable minimum or maximum set points for a programmable time period (factory set for 10 seconds), the AVR shall electronically shut off. When electrical parameters are back within acceptable limits for a programmable time period (factory set for 60 seconds), the AVR shall automatically restart to provide conditioned power to the load. If the input parameters are within acceptable limits, but the output voltage is outside of acceptable programmed limits, the AVR shall electronically shut off and require a manual restart.
The AVR shall be capable of operating at 100% rated load capacity continuously, 200% rated load for 10 seconds, 500% rated load for 1 second and 1000% rated load for 1 cycle. Operating efficiency shall be a minimum of 96%, typical at full load.
Transformer winding shall be continuous copper with electrostatic tripled shielding and K-13 rated for the purpose of handling harmonic currents.
Response Time: The AVR shall respond to any line voltage variation in 1/2 cycle while operating linear or non-linear loads, with a load power factor of 0.60 of unity. Peak detection of the voltage sine wave shall not be permitted to avoid inaccurate tap switching due to input voltage distortion.
Operating Frequency: The AVR shall be capable of operating at +10% to -15% of the nominal frequency, 50Hz or 60Hz.
Rating: this device shall be rated at 1.5kVA.
Access Requirements: The AVR shall have removable panels on the front, rear and sides as required for ease of maintenance and/or repair.
Metering: An input meter is provided to display line voltages
Ventilation: The AVR isolation transformer shall be designed for convection cooling. If fan cooling is required for the solid state electronic switching devices.

1.6                          PROJECT WORK ORGANISATION
The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:
Chapter one of this work is on the introduction to an automatic voltage stabilizer. In this chapter, the background, significance, objective limitation and problem of an automatic voltage stabilizer were discussed.
Chapter two is on literature review of an automatic voltage stabilizer. In this chapter, all the literature pertaining to this work was reviewed.
Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.
Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.
Chapter five is on conclusion, recommendation and references.

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