Design And Construction Of A Microcontroller Based Automatic Voltage Regulator For Single Phase Generator

ABSTRACT

Every electrical and electronic appliance is designed to work perfectly at a certain input voltage. In Nigeria, household electrical and electronic appliances are designed to work properly at 220VAC, 50Hz and most of the times the voltage supplied from distribution companies are as low as 80VAC making this appliances to work under threat of low voltage supply. This low supply voltage causes these appliances to malfunction and in most cases damage them. Since the electric power supply/distribution companies are unable to provide the consistent adequate voltage level (220VAC) demanded by these sensitive appliances, therefore there is need for consumers to protect the appliances from damage and ensure their safe operation, hence the use of automatic voltage stabilizers to improve the situation. In this research work, a PIC16F877A microcontroller was programmed to monitor the input voltage from distribution companies and if voltage level is between 80 VAC and 250VAC, it gives a constant output voltage of 220VAC (±6%) required by the appliance. In doing this, it constantly varies the turn’s ratio of the Auto-transformer, initiating a step-up or step-down operation of the transformer so that a regulated voltage of 220 VAC (±6%)is obtained at the stabilizer output. The design also includes an under/over voltage device protection which ensure that the device is inoperative when the supply voltage is above 250VAC. The system constructed was tested with a variable transformer. At voltages within the specific input voltage range, the regulator gave an output voltage of 220 VAC (±6%) and voltages outside the specified input range, the over/under voltage protection prevents power from being supplied to the auto- transformer thus making the stabilizer output to be 0 V. The system at this voltage alerts the user of the anomaly by displaying UNUSUAL VOLTAGE on the LCD Screen

CHAPTER ONE

1.0                                              INTRODUCTION

The development of any country is largely hinged on the availability of undisturbed and regulated power supply. In Nigeria, electricity is generated by turbine driven synchronous generators at 50Hz at a standard minimum voltage of 11kV. The generated voltage is then stepped up to the primary or secondary Grid voltage of 330kV or 132kV to reduce power losses during transmission. The generated power then travels from the generating stations to the point of utilization via high voltage Transmission lines, most of which are suspended overhead. However due to the uneven power demand at the load end and the complexity of the consumer network, a third party is required to ensure that the generated electricity is properly distributed according to the load demand, while taking into consideration the necessary geographic and economic factors as they affect the overall socio-economic growth of the nation. In Distribution, electrical power is stepped down at distribution sub-stations of various levels to a final voltage of 415V (phase to phase) and 230V (phase to neutral) which is directly consumed by most electrical load.

Nigeria power system is a typical power system that is faced with several challenges, the most basic of which includes – Insufficient generated power, lengthy transmission lines, overloading of distribution Transformers, vandalization of Transmission lines, low power factor of distribution network, lack of infrastructure maintenance, lack of system planning, etc. all of which result in reduction of the voltage level of the electric power eventually received by the consumers.

The occurrence of faults within the power system could also result in surges that cause the flow of excessive short circuit current under extremely high voltages. Even though this condition lasts for a short period of time (because of the protective measures incorporated into the system) a lot of damage can be done to our connected loads in that very short period of time.

A growing market for automatic regulator and regulators rated between 0.5 kVA and 10 kVA for the domestic market has grown. The devices have various advertised performance limitations and employ a combination of electronics to select the tappings on transformers. In an ideal situation, voltages no less than 170 volts can be readily taken care of with outputs lying within the stipulated tolerance of the supply authority’s values. Unfortunately, the unrestricted expansion of the distribution networks has led to extremely low voltages so that the typical commercially available voltage regulators are not effective for restoring some sort of acceptable operating voltage. A research work carried out reveals that the situation in practice is much worse with consumer voltages as low as 50 volts being quite possible [1]. Statistical data reveal that 22% of stabilizers purchased by consumers did not perform satisfactorily when the input supply voltage less than 160 volts. Products like Qlinks, Binatone, Philips, Super Masters, Century etc, regulate input voltage that falls within 160 volts and 260 volts, a range that does not cater for the Nigerian buyer [2].

The automatic voltage regulator presented in this paper aim at designing a suitable Automatic Voltage Regulator rated 1 KVA with output 220 VAC, when the input voltage is varying between 80 VAC and 250VAC.

• 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.

• 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.

• 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 1kVA.

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.