DESIGN AND CONSTRUCTION OF 5KVA AUTOMATIC VOLTAGE REGULATOR

BY

THE DEPARTMENT OF ELECTRICAL/ELECTRONIC ENGINEERING

COLLEGE OF ENGINEERING AND ENGINEERING TECHNOLOGY

MICHAEL OKPARA UNIVERSITY OF AGRICULTURE, UMUDIKE. ABIA STATE,

NIGERIA.

APRIL, 2025
 CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND OF THE STUDY

Voltage is the most important parameter in electrical power system and it is necessary to

maintain a constant output voltage because, it is the driving force that pushes current through the

conductor. Voltage stability is vital for safety and optimal performance of electrical appliances

(Kundur, 1994). Most electrical appliances are designed for optimal operation, maximum length

of service and safety if the power rating of the appliance is maintained. It is essential to hold the

voltage at the consumers’ premises within acceptable unit of magnitude. The bulk of the solution

lies on the development of an electronic circuit that monitors the main supply and takes the

decision on its own to initiate a switching action that will eventually lead to the load seeing a

voltage within acceptable normal range (Enemuoh et al., 2011). Fluctuation in power supply

can have adverse effects on power equipment such as radio, Television, Fan etc. which ranges

from humming, heating, fire, and damage.

Again, wide Voltage deviation from the normal supply can adversely affect equipment like

refrigerators, air conditioners, videos, television sets etc. Low voltage could cause the

compressors of refrigerators and air conditioners to develop fault and if not switched off could

heat up and get burnt (Ofor et al., 2010). It also causes malfunctioning in electronic appliances

like poor reception in radio and video signals. On the other hand, over voltage can cause many

instruments to burn out due to insulation breakdown (Kundur et al., 1999). The ultimate aim of

any electrical power supply authority is to provide the required power to the consumers under all

load conditions. At generating stations, the automatic voltage regulator (AVR) controls the

terminal voltage, but even at that, it is observed that the AVR do not provide adequate terminal
voltage responses, for that, the supply voltage continues to dwindle (Elices et al., 2004). The

classifiable, most cost effective and widely used material consists of installation of Power Supply

System (PSS) in addition to automatic voltage regulatory of the generator. Supply authorities

find it very difficult to maintain this voltage as a result of bad city planning, unplanned

distribution and unbalance in loading. As a result, voltage in most congested urban centers fall as

low as 100V and sometimes could rise to 300V. Voltage could rise momentarily when reactive

loads are switched on or off the supply network.

Excessive voltage variations are highly dangerous for the sophisticated Electrical and Electronic

Equipment such as electro-medical equipment, computers, communication equipment &

systems, process controllers etc. Most times the electric power that is supplied to homes and

companies usually has fluctuations. In most circumstances, the fluctuations are so minimal that

no one will notice. Although some equipment and units will work well with these fluctuations,

there are those that will be impacted by the fluctuations. When a voltage stabilizer is installed, it

ensures that there is a steady flow of current to electric equipment. Sensitive electronic

equipment such as pcs could easily get damaged by unexpected surge in current or unexpected

drop of the same. Voltage stabilizers store power such that the electronic units will draw power

from them and not from the main power source.

The main intention behind the usage of voltage stabilizers is to protect the devices against

voltage fluctuations. This is because each and every electrical appliance is designed to operate

under a specific voltage to give desired performance. If this voltage is below or above certain

value, the appliance would malfunction or might operate at worse condition or even it might get

damaged.
1.2 STATEMENT OF PROBLEM

The increase of voltage sensitive equipment has determined a continuous request for means able

to guarantee the supply of steady voltage independently from mains variation. Loss of data,

defective products, security failure, machinery faults and inaccurate information are only a few

examples of possible problems due to unstable supply. The voltage regulator has proved to be an

efficient answer in order to prevent from potential damages due to input voltage fluctuation.

Installing a voltage stabilizer is often the solution to ensure continuity and quality of production.

1.3 AIM AND OBJECTIVES

This project is aimed at the design and construction of an automatic A.C voltage stabilizer with a

power rating of 5KVA with a permissible input variation of 165V to 255V, giving a steady

output of 220V ∓ 10 V

The objectives of this project are:

(i) To design an automatic A.C voltage stabilizer using the principle of transformer tap

operations.

(ii) To implement the design in constructing an auto stabilizer with a rated capacity of 5KVA

(iii) To ensure that the voltage variation of the input voltage is between 185V – 255V, giving an

output voltage of 220V.

(iv) To give a neat outer package finishing to the design and ensure it is in proper working

condition.

1.4 SIGNIFICANCE OF THE PROJECT

Excessive voltage fluctuations are hazards to costly electronic and electrical equipment like T.V.

sets, VCRs, refrigerators and other scientific and medical equipment, etc. Voltage stabilizers are

used along with these equipment to protect them from damage due to wide line voltage

fluctuations. Since the Voltage stabilizer provides an output voltage with a specified limit for

supplying to load irrespective of wide fluctuation in the input voltage, independent of load power

factor and without introducing harmonic distortion it is therefore a highly important mechanism

for achieving electrical power systems stability and control.

1.5 SCOPE OF THE PROJECT

This project, the design and construction of a 5KVA automatic voltage stabilizer is basically

limited to the design and construction of an alternating current (A.C) stabilizer. Direct current,

D.C is not applicable to the design.

1.6 LIMITATION OF THE PROJECT

This project study is limited to input voltage variations ranging from 185V to 255V. This is the

permissible input voltage range of the automatic voltage stabilizer being discussed here.

1.7 PROJECT REPORT OUTLINE

The project report is outlined as follows:

Chapter one comprises of the introductory part of the study, its significance, scope and

limitations.

Chapter two comprises majorly of the relevant literatures and principles of operation of an

automatic voltage stabilizer.

Chapter three centers on the materials and methods used in the design and construction of the

voltage stabilizer system

Chapter four is design implementation, testing and evaluation of the construction.

Chapter five is the summary, conclusion and recommendation.

CHAPTER TWO

LITERATURE REVIEW

A voltage stabilizer is an electrical appliance used to feed constant voltage current to electrical

gadgets like ACs and computers, and protects them from damage due to voltage fluctuations. It

works on the principle of a transformer, where the input current is connected to primary

windings and output is received from secondary windings. When there is a drop in incoming

voltage, it activates electromagnetic relays which add to more number of turns in the secondary

winding, thus giving higher voltage which compensates for loss in output voltage. When there is

rise in the incoming voltage, the reverse happens, and, thus, the voltage at the output side

remains almost unchanged. Voltage stabilizers provide a means to regulate the supply voltage to

the load. These are not meant to provide a constant voltage output; instead it operates the load or

system in an acceptable range of voltage.

There are different types of voltage stabilizers available in today’s market from various

manufacturers. Stabilizers come with a different KVA rating for normal range (to produce 200-

240V output with 20-35V boost-buck for input range of 180-270V) as well as a wide range (to

produce 190-240V output with 50-55V boost-buck for input range of 140-300V) applications.

These are available as dedicated stabilizers for various homes as well as industrial appliances

such as air conditioners, LCD/LED TV, refrigerators, music systems, washing machines and also

available as a single large unit for all appliances. Stabilizers consume very less power, typically
about 2 to 5% of maximum load (i.e., rating of stabilizer). These are high efficiency devices,

typically 95 to 98%.

2.1 BASIC PRINCIPLE OF OPERATION OF VOLTAGE STABILIZER

The voltage regulation is required for two distinct purposes; over voltage and under voltage

conditions. The process of increasing voltage from under voltage condition is called boost

operation, whereas reducing the voltage from overvoltage condition is called buck operations.

These two main operations are essential in each and every voltage stabilizer.

As discussed above, the components of voltage stabilizer include a transformer, relays, and

electronic circuitry. If the stabilizer senses the voltage drop in incoming voltage, it enables the

electromagnetic relay so as to add more voltage from transformer so that the loss of voltage will

be compensated. When the incoming voltage is more than normal value, stabilizer activates

another electromagnetic relay such that it deducts the voltage to maintain the normal value of

voltage.

2.1.1 Boost Operation

The principle of boost operation of a voltage stabilizer is shown in figure below.

Fig. 2.1 – Boost operation of a voltage stabilizer

Here, the supply voltage is given to a transformer, which is normally a step-down transformer.

This transformer is connected in such a way that the secondary output is added to the primary

supply voltage. In case of low voltage condition, the electronic circuit in the stabilizer switches

corresponding relay such that this added supply (incoming supply + transformer secondary

output) is applied to the load.

2.1.2 Buck Operation

The principle of buck operation of a voltage stabilizer is illustrated in figure below.

 Fig. 2.2 – Buck operation of a voltage stabilizer

In buck operation, the secondary of step-down transformer is connected in such a way that
secondary output voltage is deducted from incoming voltage. Therefore, in case of incoming
voltage rise, the electronic circuit switches the relay that switches deducted supply voltage (i.e.,
incoming voltage –transformer secondary voltage) to the load circuit. In case of normal voltage
operating condition, electronic circuit switches the load entirely to incoming supply without any
transformer voltage.

These buck, boost and normal operations are same for all stabilizers whether they are normal
type or servo mechanism type stabilizers. In addition to these two main operations, voltage
stabilizer also performs lower and higher voltage cut off operations.

2.2 WORKING MODEL OF THE VOLTAGE STABILIZER

The figure below shows the working model of a voltage stabilizer that contains a step-down

transformer (usually provided with taps on secondary), rectifier, operational

amplifier/microcontroller unit and set of relays.

Fig. 2.3 – Working model of a voltage stabilizer

In this, op-amps are tuned in such way that they could sense various set voltages such as lower

cut off voltage, boost condition voltage, normal operating voltage, higher cut off voltage and

buck operating voltage.

A set of relays are connected in a manner that they trips the load circuit during higher and lower

cut off voltages and also they switch buck and boost voltages to the load circuit. A step-down tap

changing transformer has different secondary voltage tapping which are helpful for operating

operational amplifier for different voltages and also to add-up and deduct voltages for boost and

buck operations respectively. A rectifier circuit converts AC supply into DC to power-up the

entire electronic control circuit as well as relay coils.

Let us assume that this is 1 KVA single phase stabilizer that provides stabilization for voltage

range of 200 to 245 with a boost-buck voltage of 20-35 V for input voltage of 180 to 270 V. If
the input supply is, say 195 V, then operational amplifier energizes boost relay coil such that 195

+ 25 = 220V is supplied to the load. If the input supply is 260 V, corresponding op-amp

energizes buck relay coil so that 260-30 = 225 V is supplied to the load. If the input voltage is

below 180 V, corresponding op-amp switches lower cut off relay coil such that load is

disconnected from the supply. And if the supply is beyond 270 V, corresponding op-amp

energizes higher cut off relay coil and hence load is terminated from the supply.

All these values are approximate values; it may vary depending on the application. By this way,

a stabilizer operates under different voltage conditions.

2.3 RELEVANT LITERATURES

The electrical and electronic equipment for home and/or industrial applications that are made for

working via a stable AC supply with voltage range around 220/230Vrms, however the

unbalanced connected loads and the continuous changing in loads currents that lead to the AC

supply suffers from voltage fluctuation. This fluctuation leads to the necessity of using a suitable

AC voltage regulator. For this matter, many solutions based on different methodologies are

proposed.

Explanation of twelve types of 1kVA Automatic Voltage Stabilizers brands which are

commercially available for domestic applications are illustrated in Ponnle (2015). The studies in

Alamgir and Dev (2015) and Hoque (2014) focus on using multi taps transformers as power part

in the AC voltage regulation that is to overcome the instantaneous fluctuations of supply voltage.

Unstable supply voltage reflects negatively on the connected loads such as electronic and

electrical equipment like television, computer, microwave heaters and refrigerator. These studies

manipulate voltage oscillation through controlling function to avoid the voltage surge at the
connected AC loads that may damage these loads. The work in Alamgir and Dev (2015)

introduces tolerable range of 215-237 V through using several taps.

The electrical hazards, types of voltage stabilizers including servo voltage stabilizers are

illustrated in Venkatesh and Muthiah (2011). The study focuses on the electrical hazards, types

of stabilizers, servo voltage stabilizers, and the rapidly rising need for servo stabilizers. Although

of the objectives of Venkatesh and Muthiah (2011), the research feedback records reflect that the

response of the servo voltage stabilizers is slow compared to the other proposals of fully

electronic control systems.

Other studies focus on AC and DC voltage controlling system based on fully electronics design

are proposed in Attia et al. (2014a, 2014b, 2015), AlMashhadany and Attia (2014), Getu and

Attia (2015) and Attia and Getu (2015). These studies illustrate different methods of AC and/or

DC voltage regulation and supplying loads with/without PWM technique.

The work in Attia (2015) proposes a new three steps AC voltage regulator based on one step

down transformer, this study is characterized by simplicity and low cost because of the

dependence on one transformer. Other demerit in the proposed design in Alamgir and Dev

(2015) that the necessity of using multi tapes transformer. In Hoque (2014) the design and

implementation is based on a certain type of microcontroller that introduce a programmable

automatic control to cover the problem of voltage oscillation.

In Tarchanidis et al. (2013) and Nawaz and Arbab (2013), a sinusoidal pulse width modulation

(SPWM) technique is presented for regulating the unstable input AC voltage. This study of

Tarchanidis et al. (2013), proposed technique based on microcontroller unit controls an

AC/DC/AC stabilizer. The controlling function is made to rectify the unstable input AC voltage

and then a PWM inverter; the regulated voltage is produced through a filter to have pure
sinusoidal AC voltage. The challenge of the system is represented by the complexity and the

high cost. Other merit is that the design is done via general purpose discrete components.

Comparing to the above proposals, this study presents a design of an automatic AC voltage

stabilizer. The design adopts boost and buck principle of a step up/down transformers to remove

high/low voltage jumps from the actual required output.

The design comprises of various units starting from transformation unit, through rectifier, filter

unit, regulating unit to the comparator which evaluates the available voltage and the reference

voltage, then the difference in value triggers up the associated parallel cascaded relays that

connects the appropriate auto transformer tapping to produce the output voltage.

The lamination plate was procured and cut to the required shape and dimension on a cutting

machine. The number conformed with the calculated result. The sheets were vanished with

shellac, packaged and clamped in a vice. The transformer was wound in clockwise direction

circumferentially around the core. Output terminals were drawn out after completion of the

appropriate number of turns.

Fig. 2.4 – Internal structure of a voltage stabilizer

2.4 TRANSFORMER CORE CONSTRUCTION

The core material used in this work is silicon steel type of 0.5mm thickness per sheet. The limbs

and yoke of the transformer were cut to the required length using a cutting machine. The upper

and lower parts (the yoke) were drilled in the drilling machine to make provision for clamping.

The lamination sheets which were of square section were treated with shellac for purposes of

insulation. The sheets were arranged alternately and stacked. The assembled sheets were

clamped in the vice for two days to dry.

Winding Arrangement: The conductor materials were wound round the core in a clockwise

direction starting from the lowest voltage, tapings were drawn out after the number of turns have

been completed. The winding technique employed is the helical method which is done

concentrically around the core.

2.5 DESCRIPTION OF THE SYSTEM UNIT

The different sub-units of the system are:

The transformer section.

The rectifier and filter circuit

(3) The regulating and Microcontroller circuit.

(4) The switching device.

The transformation unit consists of a power transformer (specifically an auto-transformer in this

case) with multi-tapped secondary winding for provision of power to the control circuit and the

appliances requiring stable supply. The rectifier and filter circuit is responsible for rectifying and

smoothing the alternating voltage from the transformer to provide a ripple-free d.c. voltage used

to energize the regulating/comparator circuit.

The regulating and comparator unit is responsible for comparing the output voltage with

desired/reference to drive a signal that triggers the switching circuit to function appropriately.

This unit detects deviation from predetermined range of input voltage with Zener diodes as

regulators and transistors as comparator. The voltage level detector employs switching transition

connectivity using common emitter mode of connection and drives a signal that activates the

switching components to function appropriately thereby maintaining a steady output.

Protective device like fuse is incorporated in the system to check the ugly consequences of

voltage. There is power ON and OFF switch and a fuse for the normal voltage protection switch

and 30 – 300 a.c. voltmeters with light emitting diode for power indicator.

2.5.1 DESIGN OF THE TRANSFORMER

Md ∅
The emf, E= (1)
dt

By Faraday’s law of electromagnetic induction. Where M is mutual inductance.

Fig. 2.5 Sinusoidal flux variation

As shown in the figure above, flux increases from zero to maximum value ( ∅ M) in a quarter of a

cycle (1/4f), so average rate of change of flux

¿ ∅ M /1/ 4 f =∅ M/1÷ 1/4 f (2)

∅M 4f
× =4 fM wb/s (3)
1 1

Average emf per turn = 4f M volts (4)

For a sinusoidal flux variation, r s value of induced emf

E = 1.11 x average value (5)

Rms value of emf per turn = 1.11 x 4f M volts = 4.44f M (6)

Induced e f in primary winding is given as E1 = (induced emf per turn x no. of primary turns)

4.44f MN1 = 4.44N1B A (7)

A Similarly the rms value of emf induced is secondary winding

E2 = 4.44f MN2 = 4.44fBMAN2 (8)

It is seen that E1/N1 = E2/N2 = 4.44f M which implies that emf per turn is the same in both

windings. In an ideal transformer under no – load condition, V1 = E1 and V2 = E2

2.6 THE CONTROL CIRCUITRY

This is like an integrated circuit hat is made of microscopically small transistors, diodes, resistors

and components connected together. It is used as a complete audio amplifier, voltage amplifier

or comparators to mention just a few of its application. An operational amplifier (Op-Amp) is

widely used as a type of IC, which is designed to manipulate every differences in voltage. The

op-amp does the same work has comparator simply because it compares two voltages and

provide and output signal when one is bigger.

 Fi

g. 2.6 – Schematic diagram of the control circuitry

17V rms from the main is used to power the control circuit after rectification by the diode D 1 and

smoothened by the capacitor C1 through the potentiometer R1 and zener diode D2 to the transistor

first stage Q1 and Q2 and second stage to the first relay.

2.7 VOLTAGE STABILIZER SENSING OF INPUT VOLTAGES

First of all, a bridge rectifier is used to convert the input AC voltage into DC voltage, followed

by a large capacitor which smoothens out the DC voltage. A clamp circuit is connected at the

output of voltage divider circuit, this is formed by two diodes. The voltage will be clamped by

one of the diodes when it starts working in forward biased condition after receiving high voltage.

If low voltage appears at the output of voltage divider, then the other diode starts working in the

forward biased condition and clamps the voltage by -0.7. These voltages can then safely go to the

ADC of the microcontroller.

The input impedance for the ADC and the input capacitors are the two things that can affect the

proper operation of the circuit:

 If the input capacitor is very large then its discharge will be slower and we would not be able

to get fast or quick response. After using different capacitors, we found out that the capacitor

of value 22uF was best suited as its response was efficient in case of DC voltages and also

ripples.

 For the proper measurement of DC level by the ADC of PIC, we connect a capacitor at the

voltage divider output. This would provide a parallel capacitance to the internal capacitor of

ADC. Sampling time of ADC was also adjusted so that we can obtain accurate results.

2.8 CALIBRATION OF AUTOMATIC VOLTAGE STABILIZER

For the calibration purposes, a switch is placed in the circuit. When this switch is activated and

we reset the microcontroller, then the controller goes to the calibration mode. This would be the

only variable resistor that we have used in the circuit and it is needed because there can be a lot

of discrepancies in various components and their outputs in the circuit. The outputs can be

affected by the tolerance in the resistors and variations in the forward drop voltages of the

diodes, and also by many other factors. We will connect the variable resistor in our voltage

divider circuit and by changing the resistance values we can get the required output.

2.9 DESCRIPTION OF COMPONENTS

1. Bipolar Transistor

A bipolar transistor is a semiconductor device commonly used for amplification. The device can

amplify analog or digital signals. It can also switch DC or function as an oscillator. Physically, a

bipolar transistor amplifies current, but it can be connected in circuits designed to amplify

voltage or power.

There are two major types of bipolar transistor, called PNP and NPN. A PNP transistor has a

layer of N-type semiconductor between two layers of P-type material. An NPN transistor has a
layer of P-type material between two layers of N-type material. In P-type material, electric

charges are carried mainly in the form of electron deficiencies called holes. In N-type material,

the charge carriers are primarily electrons.

Fig. 2.7 – Bipolar transformer

2. Fixed resistors

A resistor is used to reduce the flow of electricity in an electric circuit. Resistors come in fixed or

variable types. A fixed resistor cannot be changed as it is set at a specific value, whereas a

variable resistor can manage flows at and below a specific level. Fixed value resistors have a

defined ohmic resistance and are not adjustable. Fixed resistors are the most commonly used

resistors and in general one of the most used electronic components.

Fig. 2.8 – Fixed resistor

3. Static relays
Solid state relay or static relay is an electrical relay, in which the response is developed by

electrical/magnetic/optical or other components without mechanical movement of components.

In static relay, the comparison or measurement if electrical quantities is done by a static circuit.

This circuit gives an output signal for the tripping of a circuit breaker. In general, static relays are

having a DC polarized relay as slave relay A static relay or solid state relay employs

semiconductor diodes, transistors, zener diodes, SCRs, logic gates etc. as its components.

4. Diode

A diode is an electrical device allowing current to move through it in one direction with far

greater ease than in the other. The key function of an ideal diode is to control the direction of

current-flow. Current passing through a diode can only go in one direction, called the forward

direction. Current trying to flow the reverse direction is blocked. Depending on the voltage

applied across it, a diode will operate in one of three regions:

1. Forward bias: When the voltage across the diode is positive the diode is “on” and current

can run through. The voltage should be greater than the forward voltage (V F) in order for

the current to be anything significant.

2. Reverse bias: This is the “off” mode of the diode, where the voltage is less than V F but

greater than -VBR. In this mode current flow is (mostly) blocked, and the diode is off. A

very small amount of current (on the order of nA) – called reverse saturation current – is

able to flow in reverse through the diode.

3. Breakdown: When the voltage applied across the diode is very large and negative, lots of

current will be able to flow in the reverse direction, from cathode to anode.
Fig. 2.9 – Diodes

5. Zener Diode

Zener diodes are a special kind of diode which permits current to flow in the forward direction.

What makes them different from other diodes is that Zener diodes will also allow current to flow

in the reverse direction when the voltage is above a certain value. This breakdown voltage is

known as the Zener voltage. In a standard diode, the Zener voltage is high, and the diode is

permanently damaged if a reverse current above that value is allowed to pass through it. Zener

diodes are designed in a way where the Zener voltage is a much lower value

6. Capacitors

A capacitor is a two-terminal, electrical component which has the ability or “capacity” to store

energy in the form of an electrical charge producing a potential difference (Static Voltage) across

its plates, much like a small rechargeable battery. In its basic form, a capacitor consists of two or

more parallel conductive (metal) plates which are not connected or touching each other, but are

electrically separated either by air or by some form of a good insulating material such as waxed

paper, mica, ceramic, plastic or some form of a liquid gel as used in electrolytic capacitors. The
insulating layer between a capacitors plates is commonly called the Dielectric. Due to this

insulating layer, DC current cannot flow through the capacitor as it blocks it allowing instead a

voltage to be present across the plates in the form of an electrical charge.

Fig. 2.10 - Capacitors

Liquid Crystal Display

Liquid Crystal Display screen is an electronic display module and find a wide range of

applications. A 16x2 LCD display is very basic module and is very commonly used in various

devices and circuits. These modules are preferred over seven segments and other multi segment

LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of

displaying special & even custom characters (unlike in seven segments), animations and so on.

ADC0804

ADC0804 is a very commonly used 8-bit analog to digital converter. It works with 0V to 5V

analog input voltage. It has single analog input and 8-digital outputs. Conversion time is another

major factor in judging an ADC, in ADC0804 conversion time varies depending on the clocking

signals applied to CLK R and CLK IN pins, but it cannot be faster than 110 μs.

Features of ADC0804:

1. 0V to 5V analog input voltage range with single 5V supply

2. Compatible with microcontrollers, access time is 135 ns

 3. Easy interface to all microprocessors

4. Logic inputs and outputs meet both MOS and TTL voltage level specifications

5. Works with 2.5V (LM336) voltage reference

6. On-chip clock generator

7. No zero adjust required

8. 0.3[Prime] standard width 20-pin DIP package

9. Operates ratio metrically or with 5 VDC, 2.5 VDC, or analog span adjusted voltage

reference

10. Differential analog voltage inputs

Fig. 2.11 – ADC0804

8051 Microcontroller

The 8051 microcontroller is an 8-bit family of microcontroller and used across worldwide.

“System on a chip” is the other synonym the 8051 microcontroller has got and ingredients like

128 bytes of RAM, four ports on a single chip, 2 Timers, 1 Serial port and 4Kbytes of ROM

signify the synonym. As it is an 8 bit processor the CPU can work very efficiently and rapidly if
the data is about 8 bits at a time and if the data is more that it has to be fragmented to various

CPU.

Fig. 2.12 – 8051 Microcontrollers

CHAPTER THREE

MATERIALS AND METHODS

This project is designed taking into cognizance the principle of transformer tap operations for

correcting and compensating overvoltage and under voltage respectively. The following are the

components utilized in the construction of the 5KVA automatic voltage:

Bipolar transistors

Fixed resistor

Transformer
Static relays

Diodes

Zener diodes

Capacitors

Vero board

Cable

13 Amp plug

13 Amp socket outlet

Switch

Variable resistor

Metallic casing.

Liquid Crystal Display

8051 Microcontroller

ADC 0804

3.1 TRANSFORMER DESIGN SPECIFICATIONS

Power rating: 5KVA

Input voltage: 185V – 255V

Output voltage: 220V ±10V

Frequency: 50 cycle/sec.

Type: Single phase core type

Cooling scheme: Air-cooled Core cross – section: Square

1. Current density – ranges from 2 – 3A/mm2 for continuously operated power devices.
2. Maximum flux density Bm spans from 1.5 to 1.7 tesla (wb/m 2) for power transformer using

cold-rolled steel laminations.

3. Weighting factor K ranges from 0.75 – 0.85 for single phase core type transformer.

4. Stacking factor 0.96-0.97 for cold rolled laminations.

5. Window space factor KW is taken as 0.33

In the design, the values taken were: S = 2.5A/m 2, Bm = 1.6 wb/m2, K = 0.80 stacking factor =

0.96, Kw 0.33, Centre to centre distance between limbs is twice the width of the core.

3.2 MAGNETIC CIRCUIT (CORE) DESIGN

(i) Voltage per turn, Vt

The output equation of a transformer is given as S = E.I x10-3 (KVA) (9)

But E = 4.44 f M N and I = M/γN (10)

∅M −3
Therefore S = 4.44 f MN x ×10 (11)
yN
2 −3
4.44 f ∅ M × 10
S= (12)
yN

Making M subject of the formula, we have:

2 SyN
M = −3 (13)
4.44 f ×10
3
2 SyN × 10
M = (14)
4.44 f

M=
√ SyN ×10 3
4.44 f
(15)

But voltage per turn Vt = E/N = 4.44f. Substituting the value of M in equation 15 into equation

16 we have
 Vt =4.44 f ×
√ y ×10 3
4.44
×S (16)

Where K = 4.44f γ x 10 3 , f is supply frequency in Hertz, S is electric rating of machine in KVA,

M is maximum flux circulating in the core in webers, γ is the ratio of magnetic loading to electric

loading (a constant), E is the impressed voltage in volts, I is the current in amperes and K is

weighting factor.

Calculating Vt yields.

Vt =0.8 √ 1.5 = 0.979795897 ≅ 0.98 (17)

To calculate Cross – sectional area of core Ai

The Emf equation is E = 4.44FN M (18)

Vt = 4.44f M = 4.44FBMAi (19)

0.98 = 4.44 x 50 x Ai = 355.2Ai (20)

0.98
Ai= = 0.002759009m2s (21)
355.2

¿ 2759.0mm2

To calculate the diameter of core cross– section (circumscribing circle)

net core area Ai

Stacking factor ¿ (22)
gross core area Ag

2759.0
0.96 ¿ (23)
Ag

2759.0 = 0.96 (0.50d2)

2 2759.0
d= =5747.92 (24)
0.96 × 0.5

d =75.8150 75.8mm

(iv) To calculate Net window area Aw

The output equation for a single phase transformer is

= S2.22fBmAi Kw Aw x 10-3 (25)

Substituting values yield

2.0 x 109 = 404248.68 Aw

9
2.0 ×10
Aw ¿ =49 = 49mm2
404248.68

3.3 ELECTRIC CIRCUIT (WINDING) DESIGN

(i) Number of turns of primary winding Np:

The expression for voltage per turn is given as; Vt = E/N

Where N is number of turns and E is induced voltage.

Therefore Np = E/Vt (26)

240
E is 240 for primary circuit Np ¿
0.98

244.897 = 245turns

(ii) Number of turns of secondary winding (tapings) Ns

The secondary windings consist of many tapings, each outputting voltages but within the range

of 240v ±1%.

237.6 243 turns

NS ¿ 0.98 =242.448 ≅
min

242.4
NSmax ¿ =247.346 ≅ 247 turns
0.98

3.4 BLOCK DIAGRAM OF THE AUTOMATIC VOLTAGE STABILIZER

Fig. 3.4 Block diagram of the Automatic Voltage Regulator

Fig 3.4 is the block diagram for a typical automatic voltage regulator. As seen in the block

diagram, the transformer step down the A.C input voltage to suit the requirement of the

electronic devices and the circuits fed by the D.C power supply. It also provides isolation from

the supply line, which is a safety consideration.

The stepped down voltage undergoes rectification in order to convert the a.c voltage into

pulsating d.c voltage. The pulsating d.c voltage is then passed for filtration in order to remove

the fluctuation or pulsations (called ripples) present in the output voltage supplied by the

rectifier.

Voltage regulation involves comparing the output voltage against an internal reference voltage.

If there is any difference between the two voltages, the voltage regulator will automatically
compensate to provide the right output. The regulation element in a voltage regulator will start

producing more or lesser voltage depending on a low or high output voltage reading. The task of

the voltage regulator is to make sure the voltage stays as close to the prefixed level as possible.

This induces two variables, the speed of response of the voltage regulator and its stability.

The voltage divider functions to provide different D.C output to different electronic circuits.

The Microcontroller, the ADC and the Relays make up the voltage stabilizing circuitry of the

Control Unit.

The Liquid Crystal Display, is interfaced with the Microcontroller and didtally displays the

output voltage of the AVS.

3.5 CIRCUIT DIAGRAM OF THE AVS

Fig. 3.5 – Circuit diagram of automatic voltage stabilizer

The proposed circuit of a simple 5KVA automatic voltage stabilizer circuit is shown above.

The microcontroller generates the control signals and three relays are used with the

autotransformer for the control and conversion of voltage. The input voltage is sensed by the

microcontroller and it tries to keep the output voltage between its specified ranges, by switching

the relays. Out of the three relays, two of them switch the connection between the tappings,

185V and 255V, one switches the output connection between the tappings 200 and 240 while the

last one is a master on/off relay which disconnects the output in case of low and high cut modes.

Relay interfacing with microcontroller is very easy.

A bridge rectifier is used to convert the input AC voltage into DC voltage, followed by a large

capacitor which smoothens out the DC voltage. By using a voltage divider circuit the DC voltage

is stepped down so that the microcontroller can accept it. After long speculation and

experimentation, the ratio for the resistors of voltage divider circuit was chosen to be

(47kΩ*6):3.3kΩ. The circuit in this ratio performs better and the power dissipation is also

reduced.

A clamp circuit was connected at the output of voltage divider circuit, this is formed by two

diodes. The voltage will be clamped by one of the diodes when it starts working in forward

biased condition after receiving high voltage. It would be approximately 5.7V.If low voltage

appears at the output of voltage divider, then the other diode starts working in the forward biased

condition and clamps the voltage by -0.7. These voltages can then safely go to the ADC of the

microcontroller. Schottky diodes can be used to improve the clamping of voltages.

The input impedance for the ADC and the input capacitors are the two things that can affect the

proper operation of the circuit:

 REFERENCES
Al-Mashhadany, Y.I. and H.A. Attia, (2014). Novel design and implementation of portable
charger through low-power PV energy system. Adv. Mater. Res., 925: 495-499.
Alamgir, M.S. and S. Dev, (2015). Design and implementation of an automatic voltage regulator
with a great precision and proper hysteresis. Int. J. Adv. Sci. Technol., 75: 21-32.
Attia, H., (2015). Three steps AC voltage regulator based on one step-down transformer. Int. J.
Appl. Eng. Res., 10(19): 39898-39902.
Attia, H.A. and B.N. Getu, (2015). Design and simulation of remotely power controller. Int. J.
Appl. Eng. Res., 10(12): 32609-32626.
Attia, H.A., B.N. Getu, H. Ghadban and A.K. Abu Mustafa, (2014a). Portable solar charger with
controlled charging current for mobile phone devices. Int. J. Therm. Environ. Eng., 7(1):
17-24.
Attia, H.A., Y.I. Al-Mashhadany and B.N. Getu, (2014). Design and Simulation of a High
Performance Standalone Photovoltaic System. In: Hamdan,
Attia, H.A., B.N. Getu and N.A. Hamad, (2015). Experimental validation of DTMF decoder
electronic circuit to be used for remote controlling of an agricultural pump system.
Proceeding of the International Conference on Electrical and Bio-
F.O. Enemuoh, C.O. Ohaneme, B.I. Onyedika (2011). “The design concept and operating
principle of voltagesensitive switching circuit [VSSC]”, Journal of engineering and
Applied Sciences, March 2011, page 51-56.
Hussain A. Attia . (2016). Binary Weighted 7-steps Automatic Voltage Regulator
Research Journal of Applied Sciences, Engineering and Technology 12(9): 947-954
Matthew E. Oboh, Jafaru Braimah, (2014). Single Phase Automatic Voltage Regulator Design
for Synchronous Generator. International Journal of Scientific & Engineering Research,
Volume 5, Issue 12, December.
Mustapher, Wasin Adewole (2004) “Design and Construction of 2KVA automatic voltage
regulator with input voltage range 100 – 260v”, Federal University of Technology Akure.
Ofor, N.P. and Ibrahim, A.G(2010). “Construction and Characterization of a designed 500VA
transistor Controlled Inventor”, Natural and Applied Sciences journal vol. II No.1 108,
2010.

Kundur, P. (1994). “Power System Stability and Control”, Mc Graw – Hill Inc

Kundur, P., M. Klein and G.J. Rogens, (1999)“Application of Power system stabilizers for
enhancement of overall system stability” IEEE Trans. Power System, Vol. 14, Pp 614-
626 May,

Ponnle, A.A., (2015). Performance of domestic AC voltage stabilizers in meeting low voltage
problems in Nigeria: A case study of 12 different brands. Int. J. Eng. Technol., 5(6): 358-
367.
Tarchanidis, K.N., J.N. Lygouras and P. Botsaris, (2013). Voltage stabilizer based on SPWM
technique using microcontroller. J. Eng. Sci. Technol. Rev., 6(1):
38-43.
Venkatesh, S. and K. Muthiah, (2011). Powerfluctuations-usage of servo voltage stabilizers in
industries. Int. J. Appl. Eng. Res., 2(1): 283-289.