1

DESIGN AND CONSTRUCTION OF AN

LDR BASED 3-PHASE AUTOMATIC

SWITCH

BY

JIBRIN AROME KASSIM

TEC/10/ELE/00626

JANUARY, 2016

2

3

DESIGN AND CONSTRUCTION OF AN

LDR BASED 3-PHASE AUTOMATIC

SWITCH

BY

JIBRIN AROME KASSIM

TEC/10/ELE/00626

JANUARY, 2016

i

BAYERO UNIVERSITY KANO

DESIGN AND CONSTRUCTION OF AN LDR BASED 3-PHASE

AUTOMATIC SWITCH

BY

AROME KASSIM JIBRIN

TEC/10/ELE/00626

“A PROJECT SUBMITTED TO THE DEPARTMENT OF ELECTRICAL

ENGINEERING, BAYERO UNIVERSITY, KANO, IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF BACHELOR OF

ENGINEERING (ELECTRICAL)”

SUPERVISED BY

ENGR. NASIRU BELLO KADANDANI

JANUARY, 2016

ii

DECLARATION

I hereby declare that the contents of this project are the original work of my research under the

supervision of Engr. Nasiru Bello Kadandani. To the best of my knowledge, all external sources

used in this project to provide guidance have been duly acknowledged as reference.

_______________________________

JIBRIN AROME KASSIM

TEC/10/ELE/00626

21/01/2016

iii

CERTIFICATION

This is to certify that this project was fully carried out by JIBRIN AROME KASSIM with

Registration Number TEC/10/ELE/00626, Electrical Engineering Department, Faculty of

Engineering, Bayero University Kano, Nigeria.

__________________ _________________

ENGR. N.B. KADANDANI DATE

PROJECT SUPERVISOR

______________________ __________________

ENGR. DR. BALA B. BUKATA DATE

PROJECT COORDINATOR

__________________________ __________________

DR. S.I. BIRNIN KUDU DATE

HEAD OF DEPARTMENT

iv

DEDICATION

This work is dedicated to my parents Mr. and Mrs. Mohammed Jibrin and also my sisters;

Zainab and Saratu Jibrin for their constant support and prayer. I also dedicate this work to

my supervisor Engr Nasiru B. Kadandani for his guidance throughout my research work.

It is also dedicated to my lecturers in the Department of Electrical Engineering, Bayero

University Kano.

v

ACKNOWLEDGEMENT

This work would not have been a complete success; if not the assistance, advice and moral support

I received from various individuals. First of all my most sincere gratitude and indebtedness go to

Engr. Nasiru B. Kadandani my supervisor who has given me not only valuable advice and

suggestions but showed me tolerance and patience in the course of this work. I am also grateful to

all the lecturers in Electrical Engineering Department, Bayero University Kano for their support

throughout the period of my studies. My hearty appreciation goes to my family who have provided

unconditional support throughout my life. I also wish to express my gratitude to so many friends

of mine who have been so helpful throughout my stay in this University.

vi

ABSTRACT

The design and construction of automatic lighting switch is carried out so as to

automatically switch on lightings during dark hours. This system uses a photocell sensor

that has a light dependent resistor as the primary sensor. The photocell is designed and

constructed in such a way as to detect the presence of a dark environment and switch on

all lightings and during bright hours of the day it switches off the light on sensing a bright

environment. Within the limit of the available components used, the implementation of

this project yielded the required result with a reliability of 88.6% performing satisfactorily

according to the design implementation.

vii

TABLE OF CONTENTS

DECLARATION ............................................................................................................................ ii

CERTIFICATION ......................................................................................................................... iii

DEDICATION ............................................................................................................................... iv

ACKNOWLEDGEMENT .............................................................................................................. v

ABSTRACT ................................................................................................................................... vi

SYMBOLS AND ABBBREVIATION ........................................................................................ xii

CHAPTER ONE ............................................................................................................................. 1

GENERAL INTRODUCTION ....................................................................................................... 1

1.1 INTRODUCTION ............................................................................................................ 1

1.2 STATEMENT OF THE PROBLEM ............................................................................... 2

1.3 AIM AND OBJECTIVES OF THE PROJECT ............................................................... 2

1.4 METHODOLOGY .......................................................................................................... 2

1.5 MOTIVATION AND SIGNIFICANCE OF THE PROJECT ......................................... 3

1.6 SCOPE AND LIMITATION ........................................................................................... 4

1.7 ORGANIZATION OF REPORT ..................................................................................... 4

CHAPTER TWO ............................................................................................................................ 6

LITERATURE REVIEW ............................................................................................................... 6

2.1 INTRODUCTION ............................................................................................................ 6

2.2 BRIEF OVERVIEW OF SIMILAR PAST PROJECT .................................................... 6

2.3 MAJOR COMPONENTS DESCRIPTION ................................................................... 8

2.4 CONTACTOR ........................................................................................................ 8

2.5 AUXILIARY CONTACTOR 10 2.6 CIRCUIT BREAKER 12

2.7 ROTARY SWITCH 13 2.8 RESISTOR 13 2.9 CAPACITOR 14 2.10 DIODE 16

2.11 TRANSISTOR 16 2.12 RELAY 17 2.13 LIGHT DEPENDENT RESISTOR 18

2.14 CONCLUSION ......................................................................................................... 19

CHAPTER THREE ...................................................................................................................... 20

DESIGN AND ANALYSIS ......................................................................................................... 20

3.1 INTRODUCTION ......................................................................................................... 20

3.2 FILTER 20 3.3 IN-RUSH LIMITING CURRENT RESISTOR 22

viii

3.4 RECTIFICATION 23

3.5 VOLTAGE REGULATION 24 3.6 THE SENSING CIRCUIT 24 3.7 POWER SUPPLY 31

3.8 PROTECTIVE UNIT (CIRCUIT BREAKER) 31 3.9 THERMAL CONSTRAINT 31 3.10 CABLE SELECTION 31 3.11 VOLTAGE DROP 32 3.12 EARTH FAULT LOOP IMPEDANCE 33

3.13 RESISTANCE OF THE CABLE 34 3.14 AREA OF CABLE 34 3.15 TRUNKING 35 3.16 ENERGY CONSUMPTION CALCULATION 37

3.17 POWER CONSUMPTION IN 24 HOURS FOR LIGHTING WITHOUT

PHOTOCELL 38

3.18 POWER CONSUMPTION FOR ESTIMATED 11-HOURS USING PHOTOCELL

38

3.19 YEARLY POWER GAINED AS A RESULT OF THE AUTOMATIC SWITCHING

39 3.20 CONCLUSION ......................................................................................................... 39

CHAPTER FOUR ......................................................................................................................... 41

CONSTRUCTION AND TESTING ............................................................................................ 41

4.1 INTRODUCTION .......................................................................................................... 41

4.2 CONSTRUCTION ......................................................................................................... 41

4.3 COMPONENTS USED FOR CONSTRUCTION ......................................................... 41

4.4 CONSTRUCTION MATERIALS ................................................................................. 42

VERO BOARD 42

TEST BOARD 42 SOLDERING IRON 42 SOLDERING LEAD WIRE 42

SUCKER 42 JUMPERS 42

4.6 TESTING ....................................................................................................................... 43

4.7 RELIABILITY TEST 43

4.8 ASSESSEMENT OF EQUIPMENT/SYSTEM RELIABILITY 43

4.10 RESULTS .................................................................................................................. 47

4.11 DISCUSSION OF RESULTS .................................................................................... 47

4.12 PRINCIPLE OF OPERATION .................................................................................. 48

4.13 SAFETY PRECUATION .......................................................................................... 52

4.14 APPLICATIONS OF THE SYSTEM ........................................................................ 52

4.15 CONCLUSION .......................................................................................................... 52

ix

CHAPTER FIVE .......................................................................................................................... 54

SUMMARY, CONCLUSION AND RECOMMENDATION ..................................................... 54

5.1 SUMMARY ................................................................................................................... 54

5.2 CONCLUSION .............................................................................................................. 54

5.3 RECOMMENDATIONS FOR FUTURE SCOPE OF WORK ..................................... 55

5.4 REFERENCES ............................................................................................................... 56

x

LIST OF FIGURES

Figure Number Title Page

Figure 2.1 Contactor 10

Figure 2.2 Auxiliary Contactor 11

Figure 2.3 Circuit Breaker 12

Figure 2.4 Rotary Switch 13

Figure 2.5 Resistor 14

Figure 2.6 Capacitor 15

Figure 2.7 Symbol of Diode 16

Figure 2.8 Symbol of Transistor 17

Figure 2.9 Symbol of an Electromagnetic Relay 18

Figure 2.10 Light Dependent Resistor 19

Figure 3.1 Circuit Diagram of the Photocell Power Supply Unit 22

Figure 3.2 Circuit Diagram of Sensor Circuit 25

Figure 4.1 Casing 46

Figure 4.2 Main components of the System 49

Figure 4.3 Photocell Circuit Diagram 50

Figure 4.4 Automatic Switch Circuit Diagram 49

xi

LIST OF TABLES

Table Number Title Page

Table 4.1 Reliability of the individual component used. 44

Table 4.2 Results of the 3-phase LDR automatic switch 47

xii

SYMBOLS AND ABBBREVIATION

Symbol Quantity

NO - Normally open

NC - Normally closed

Ω - Ohms

V - Volts

A - Amperes

LDR - Light dependent resistor

P - Power

D.C - Direct Current

A.C - Alternating Current

LED - Light Emitting Diode

W - Watt

PCB - Printed Circuit Board

PIV - Peak Inverse Voltage

1

CHAPTER ONE

GENERAL INTRODUCTION

1.1 INTRODUCTION

Despite Nigeria’s early experiment with electricity generation and supply, the country has not met

40 per cent of her electricity consumption requirement for both industrial and domestic uses.

To meet the shortfall in the nation’s electricity demand and supply other sources of electricity

supplies were turned to without much significant success recorded but with much negative impact

on the environment. Most of the electricity supply in Nigeria is provided by generators, using fossil

oil and gas [1].

Experts in electricity generations, supply and environmentalists are also of the concerns that with

Nigerian population estimated to hit between 257million people by 2030 the demand for energy

would continue to rise [2], with these knowledge methods of reduction in power wastage should

be adopted, a typical example is as stated in this report.

An automatic light control switch is a switch which activates and deactivates depending on the

condition of light (light intensity). It turns the light on with the gradual decrease in light intensity,

and turns the light off with the gradual increase in light intensity. The light remains on for any

duration depending upon the condition of the light intensity [3].

Nowadays rapid development and rapid growth of industrial estate turns remote villages into cities,

the need for lighting is directly proportional to the method in which the light should be controlled.

The purpose of this project is to design and construct an automatic switching control for streetlight,

premises, social centers and estates which is aimed at providing a convenient and comfortable

driving system especially in the very dark hours of the day.

2

It consists of discrete and solid state devices such as Light Dependent Resistor, Circuit breaker,

Contactor, fuse, auxiliary contactor, indicator lamps which were coupled together to achieve the

desired performance.

1.2 STATEMENT OF THE PROBLEM

The total lack of effective power consumption control has added to the problem of dwindling

power generated from the load centres. The total absence or lack of sufficient security systems as

a result of absence of manual switching personnel in homes has caused a great deal of discomfort

to home owners, business sector, store, restricted areas leading to a high rate of theft coupled with

the increasing rate of accidents on our highways as a result of poor visibility due to streetlight not

being turned on at the right time.

1.3 AIM AND OBJECTIVES OF THE PROJECT

The aim of this proposed system is to provide automated switching function with the use of

photocell (LDR) to automatically switch on lighting when the day gets dark and switch off when

it gets bright.

The objectives of the project are:

1. To design and construct a photocell sensor for sensing light intensity.

2. To design and construct an automatic lighting switch that can be used to switch on the load

attached to it.

1.4 METHODOLOGY

The design and construction of an automatic lighting switch consists of the power supply unit,

sensor unit, control unit and display unit. The power supply unit will be implemented using a

3

3phase single throw 415V circuit breaker which serves to provide power to the other components

for the switching function.

The power supply to the photocell circuit is provided by a 220V ac power circuit which is then

rectified by the full wave bridge rectifier to 12V dc and capacitor C2 performs the filtration before

it is transferred to the relay which then gives an output to our ac load i.e. light.

The sensory unit will be designed using a light dependent resistor which serves as the primary

sensing element of the circuit with the relay that switches between normally open and normally

closed using two transistor connected in darlington pairs to amplify the gain.

Relay is implemented so as to oscillate between normally open and normally closed which is

configured to automatically switch on the contactor or to be set at normally closed so as to bypass

the light dependent resistor and provide manual switching function.

The initial power 220V ac supplied to the photocell was gotten from the 3phase automatic switch

which is first passed through a circuit breaker to serve as the primary protection device which

protects the circuit from fault current. The contactor serves to make or break the circuit

automatically while signal is transferred from the auxiliary contactor to the indicator lamps to

indicate the state of operation of the circuit.

1.5 MOTIVATION AND SIGNIFICANCE OF THE PROJECT

1. Given the current state of the power sector and its irregular supply, there is a need to look

into all means of reducing unwarranted power consumption. Most outdoor lighting are

usually left on throughout the whole day which amount in totality to a very high amount

of power consumption. Nowadays, human has become too busy and he is unable to find

time even to switch the lights wherever not necessary. This can be seen more effectively

4

in the case of street lights. The present system is like, the street lights will be switched on

in the evening before the sun sets and they are switched off the next day morning after

there is sufficient light on the roads. But the actual timings for these street lights to be

switched on are when there is absolute darkness. With this, the power will be wasted up to

some extent. This project gives the best solution for electrical power wastage. Also the

manual operation of the lighting system is completely eliminated except when needed.

2. The significance of this system is that there is no delay in switching process and lights are

switched on and off as at when due which would have been different if the switching

operation were carried out by a human.

The system provides a simple means of automatically switching lighting with dependency

on environmental luminance (bright or dark) and also switches on devices that are light

dependent.

1.6 SCOPE AND LIMITATION

The automatic lighting switch consists of a photocell sensor which is set so as to detect the current

state of illumination, when it detects darkness it sends a signal to the contactor to switch on and

later when the Light dependent resistor detects that the luminance level is high, it sends another

signal to the contactor to switch off all existing loads.

Since the project is built based on practical purpose, there is a limit to the amount of load that it

can performing switching operation on.

1.7 ORGANIZATION OF REPORT

This project is divided into five chapters which are meant to give an insight into the design and

implementation of this project work.

5

An introduction to the proposed project is given in Chapter One. Chapter Two entails Literature

Review. Chapter Three explains the Design and Analysis involved in this project. Chapter Four

explains the construction and testing in implementing the project, coupled with the

advantages/disadvantages and areas of application of the project. The final chapter contains the

conclusion and recommendations for future works on the project.

.

6

CHAPTER TWO

LITERATURE REVIEW

2.1 INTRODUCTION

This chapter present some literature review of related project topic that was reviewed in the process

of carrying this project. Also brief discussion was made on the various components that was used.

2.2 BRIEF OVERVIEW OF SIMILAR PAST PROJECT

Past projects were reviewed in the process of designing this project, the design and construction

of automatic light control.

Ashiru, S. [1] carried out design and construction of automatic light control switch. The LDR

senses the light energy and it resistance is reduce which allow conduction for the duration of the

light energy.

When supply is on, LC 741 is used as a compilation where a condenser microphone is used to pick

up audio signals. Any sound makes the voltage at pin 2 of 741 low and output at pin 6 high, the

sound level required to make the output high.

Another project carried out by Farzana Y. and Mohammed A. S. [2] was the design and

construction of an Automatic light control by using microcontroller based LDR. A light dependent

sensor interfaced to the microcontroller is used to track sunlight and when the sensors goes dark

the led will be made on and when the sensors found light the led will be made off.

The resistivity value is input in ADC5 (28 no pins) to ATmega 8 microcontroller. The output

comes from PB1 port of the microcontroller, PB0 and PB1 (1 and 2 no pins) port is connected with

a single female pin header connector which can debug the circuit AVCC and AREF port (20 and

7

21 no pin) connected with a capacitor in series. Pin 7 and Pin 8 connected to VCC and GND

connections of ATmega 8 microcontroller.

Also among our project review was the project carried out by Dauda M. [3] which was the design,

construction and testing of a dual relay automatic wall switch. The WA-300 dual relay automatic

wall switch turns lighting on and off based on occupancy and ambient light levels. In addition to

the relay control capabilities, the wall switch features two auto off push button on the front of the

sensor that affects the secondary relay, allowing for light level control of the secondary lighting

load.

The Automatic lighting control switch using SCR turns lighting on and off based on the level or

brightness of light. During the bright hours of the day, a very high resistance blocks the flow of

current across the SCR and it does not light up but during dark hour the LDR allows the flow of

current and there is a drop in resistance across the SCR which allows the light to turn on.

Isah, S. [4] also carried out a similar project which was the design and construction of an automatic

room light control. It was aimed at providing room light control using discrete component such as:

Light Dependent Resistors (LDRs), logic gates, 555 timers, transistors, darlington pairs, counters,

relays and diodes. As a result, a lot of components were used in the project, thereby leading to

greater cost. The counter used was a decade counter and therefore, it was able to count from 0-9.

This would mean that if a tenth person enters a room, the lights will go off again. Furthermore,

due to the discrete components used, the design of the circuit was somewhat difficult.

Another related project reviewed is by Balarabe G. [5] tilted ‘design and construction of automatic

street, tower and security lighting control system The circuit begin with the sensing circuit, which

consist of the light dependent resistor (LDR), the resistance of the LDR increases with darkness

8

while the resistance decreases with light. This process enable the transistor Q1 to be bias with the

presence of light, also when transistor Q1 is bias that is in its conduction state, transistor Q2 will

be in its non-conduction state and transistor Q3 will be in its conduction state. Similarly, when Q2

is bias that is presence of darkness on LDR, Q1 and Q3 will be in their non-conduction state, this

will enable the astable multivibrator circuit which in turn triggered the TRIAC into conduction

and lighting system is turn ON until light fell on the LDR.

The power supply to this circuit is provided by a 5V dc regulated power circuit which is use for

circuit operation.

This project (design and construction of automatic lighting switch using photocell with manual

override) therefore attempts to address the issues above by using a sensing circuit and three phase

automatic lighting switch which has application in street lighting and industries. This was achieved

by the use of contactor, rotary switch, auxiliary contactor and circuit breaker.

2.3 MAJOR COMPONENTS DESCRIPTION

The following components were used in the design and construction of this project.

2.4 CONTACTOR

A contactor is an electrically controlled switch used for switching a power circuit, similar to

a relay except with higher current ratings. A contactor is controlled by a circuit which has a much

lower power level than the switched circuit.

Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a

contactor is not intended to interrupt a short circuit current. Contactors range from those having a

breaking current of several amperes to thousands of amperes and 24 V DC to many kilovolts. The

physical size of contactors ranges from a device small enough to pick up with one hand, to large

9

devices approximately a meter (yard) on a side. Contactors are used to control electric

motors, lighting, heating, capacitor banks, thermal evaporators, and other electrical loads.

Unlike general-purpose relays, contactors are designed to be directly connected to high-current

load devices. Relays tend to be of lower capacity and are usually designed for both normally

closed and normally open applications. Devices switching more than 15 amperes or in circuits

rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low

current contacts, contactors are almost exclusively fitted with normally open ("form A") contacts.

Unlike relays, contactors are designed with features to control and suppress the arc produced when

interrupting heavy motor currents.

When current passes through the electromagnet, a magnetic field is produced, which attracts the

moving core of the contactor. The electromagnet coil draws more current initially, until

its inductance increases when the metal core enters the coil. The moving contact is propelled by

the moving core; the force developed by the electromagnet holds the moving and fixed contacts

together. When the contactor coil is de-energized, gravity or a spring returns the electromagnet

core to its initial position and opens the contacts.

For contactors energized with alternating current, a small part of the core is surrounded with a

shading coil, which slightly delays the magnetic flux in the core. The effect is to average out the

alternating pull of the magnetic field and so prevent the core from buzzing at twice line frequency.

Because arcing and consequent damage occurs just as the contacts are opening or closing,

contactors are designed to open and close very rapidly; there is often an internal tipping point

mechanism to ensure rapid action.

10

Figure 2.1 (b): Symbol of a contactor

Rapid closing can, however, lead to increase contact bounce which causes additional unwanted

open-close cycles. One solution is to have bifurcated contacts to minimize contact bounce; two

contacts designed to close simultaneously, but bounce at different times so the circuit will not be

briefly disconnected and cause an arc.

A slight variant has multiple contacts designed to engage in rapid succession. The first to make

contact and last to break will experience the greatest contact wear and will form a high-resistance

connection that would cause excessive heating inside the contactor. However, in doing so, it will

protect the primary contact from arcing, so a low contact resistance will be established a

millisecond later.

Another technique for improving the life of contactors is contact wipe; the contacts move past each

other after initial contact on order to wipe off any contamination.

Figure 2.1 (a): physical appearance of Contactor

Figure 2.1: Contactor

2.5 AUXILIARY CONTACTOR

One of the main uses of auxiliary contacts is the electrical retainer circuit. This is a control circuit

function that allows the use of momentary, push type buttons to start motors and other equipment.

Another common function of these contacts is remote status and trip indication. A separate, low

voltage circuit is run through the auxiliary to a remote indication lamp that illuminates when the

11

device is activated or trips. Auxiliary contact points may also be used to switch on auxiliary

equipment, such as starter panel cooling fans, when the contactor activates.

There are two basic auxiliary contact types: those that are closed in the non-activated state or those

that are open. These are known as normally closed (N/C) and normally open (N/O) contacts. The

N/C contacts are, for example, used as electrical interlocks where two contactors are used for

forward/reverse operation. The control circuit for one contactor will run through the N/C auxiliary

on the other. This means that one cannot be inadvertently started while the other is operating. The

N/O contacts are generally used to switch on status indication lamps and act as retainer circuits.

Many circuit breakers and contactors have auxiliary contacts built in as an integral feature.

Additional sets of contacts may however be added should the need arise. These modules typically

slide on the top of smaller relays or snap onto the existing auxiliary set.

Figure 2.2 (a): Physical appearance of

an Auxiliary Contactor

Figure 1.2: Auxiliary Contactor

Figure 2.2 (b): Symbol of an Auxiliary

contactor

12

Figure 2.3 (b): Symbol of a Circuit breaker

2.6 CIRCUIT BREAKER

When electricity enters your home, it goes to a circuit breaker box (or fuse box in older homes),

where it is divided into a number of circuits. Each circuit is protected by a breaker or fuse.

Bedrooms, living rooms and family rooms where only lights, alarm clocks and other small

electrical items are usually used are normally on 15-amp circuits. Kitchens, laundry rooms,

bathrooms and dining rooms places where you're more likely to use toasters, irons, hair dryers and

other big-watt items are usually served by heavier-duty, 20-amp circuits. Major appliances like

5,000-watt electric water heaters and 10,000-watt electric ranges demand so much electricity that

they take their own 30- to 50-amp dedicated circuit.

The circuit breaker, the wire and even the wire insulation are all designed to work as a system and

that system has limits. Try to push more current through a circuit than it's designed for and things

start happening. Wires heat up under the burden of carrying the excess current. When this happens,

the insulation around the wire can degrade or even melt. When insulation melts, current is no

longer confined within the wire, that's when fires start. Luckily, the circuit breaker senses the

excess current and trips to stop the flow of power before damage occurs.

Figure 2.3 (a): Physical appearance

of a Circuit breaker

Figure 2.2: Circuit Breaker

13

2.7 ROTARY SWITCH

A rotary switch consists of a rotor that has a contact arm or spoke which projects from its surface

like a cam. It has an array of terminals, arranged in a circle around the rotor, each of which serves

as a contact for the "spoke" through which any amount of different electrical circuits can be

connected to the rotor. The switch is layered to allow the use of multiple poles, each layer is

equivalent to one pole.

Figure 2.4: Rotary Switch

The following components were used in the design and construction of this project.

2.8 RESISTOR

Resistors come in a variety of sizes, related to the power they can safely dissipate. Colour-coded

stripes on a real-world resistor specify its resistance and tolerance. Larger resistors have these

specifications printed on them.

Any electrical wire has resistance, depending on its material, diameter and length. Wires that must

conduct very heavy currents (for example ground wires on lightning rods) have large diameters to

reduce resistance.

The power dissipated by a resistive circuit carrying electric current is in the form of heat. Circuits

dissipating excessive energy will literally burn up. Practical circuits must take power capacity into

account.

Ohm's law states that current flow depends on circuit resistance:

14

I = 𝑉

𝑅 … (2.1)

Circuit resistance can be calculated from the current flow and the voltage

R = V

I … (2.2)

Connecting resistors in series can increase circuit resistance:

R = R1 + R2 + ⋯ + 𝑅𝑛 … (2.3)

Placing one resistor in parallel with another can reduce circuit resistance:

R = 1

𝑅1 +

1

𝑅2 +

1

𝑅𝑛 … (2.4)

Connecting resistors in series can increase circuit resistance:

Figure 2.5 (a): Fixed resistor

2.9 CAPACITOR

A capacitor stores electrical energy in the form of an electrostatic field. Capacitors are widely used

to filter or remove AC signals from a variety of circuits. In a DC circuit, they can be used to block

the flow of direct current while allowing AC signals to pass.

Figure 2.5: Resistor

Figure 2.5 (b): Variable resistor

15

The capacity of a capacitor to store energy is called its capacitance, C, which is measured in farad.

It can have any value from pF to mF. Capacitors in an AC circuit behave as "short circuits" to AC

signals. They are widely used to filter or remove AC signals from a variety of circuits--AC ripple

in DC power supplies, AC noise from computer circuits, etc.

Capacitors prevent the flow of direct current in a DC circuit. They can be used to block the flow

of DC, while allowing AC signals to pass. Using capacitors to couple one circuit to another is a

common practice.

Capacitors take a predictable time to charge and discharge and can be used in a variety of time-

delay circuits. They are similar to inductors and are often used with them for this purpose.

The basic construction of all capacitors involves two metal plates separated by an insulator.

Electric current cannot flow through the insulator, so more electrons pile up on one plate than the

other. The result is a difference in voltage level from one plate to the other.

The current through the capacitor is equal to C multiplied by the rate of change in voltage across

the capacitor, that is:

I = C𝑑𝑣

𝑑𝑡 … (2.5)

Figure 2.6 (a): Fixed

Figure 2.6: Capacitor

Figure 2.6 (b): Variable Figure 2.6 (c): Fixed and

Polarised

16

2.10 DIODE

Diodes exhibit a number of useful characteristics, such as predictable capacitance (that can be

voltage controlled) and a region of very stable voltage. They can, therefore, be used as switching

devices, voltage-controlled capacitors (varactors) and voltage references (Zener diodes).

Because diodes will conduct current easily in only one direction, they are used extensively as

power rectifiers, converting AC signals to pulsating DC signals, for both power applications and

radio receivers.

Diodes behave as voltage-controlled switches, and have replaced mechanical switches and relays

in many applications requiring remote signal switching.

Even indicator lamps are now replaced with diodes (LEDs) that emit light in a variety of colours

when conducting.

A special form of diode, called a Zener diode, is useful for voltage regulation.

2.11 TRANSISTOR

A bipolar junction transistor, or BJT, is a current-based valve used for controlling electronic

current. BJTs are operated in three different modes, depending on which element is common to

input and output common base, common emitter or common collector

Figure 2.7(a): Diode Figure 2.7 (b): LED Figure 2.7 (c): Full-wave

rectifier

Figure 2.7(d):

Regulator diode

Figure 2.7: Symbols of Diode

17

A transistor can be operated in its non-linear region as a current/voltage amplifier or as an

electronic switch in cut-off and saturation modes. In its linear region, it must be biased

appropriately (i.e., subjected to external voltages to produce a desired collector current) to establish

a proper DC operating point.

BJTs are commonly used in amplification and switching applications. They come in two versions:

NPN and PNP. The letters refer to the polarities, positive or negative, of the materials that make

up the transistor sandwich. For both NPNs and PNPs, the terminal with the arrowhead represents

the emitter.

An NPN transistor has two n-regions (collector and emitter) separated by a p-region (base), the

terminal with the arrowhead is the emitter while a PNP transistor has two p-regions (collector and

emitter) separated by an n-region (base). The terminal with the arrowhead represents the emitter.

2.12 RELAY

A relay is a device, which function as an electrically operated switch. Relays have much

application. There are different types of relays;

i. Electromagnetic relay

ii. Crystal can relay

iii. Dry read relay

iv. Mercury wetted relay

Figure 2.8: Symbols of transistor

Figure 2.8(b): PNP Transistor Figure 2.8 (a): NPN Transistor

18

v. Solid state relay

vi. Time delay relay

Relay can be used for the following applications:

i. Control of high power load circuits.

ii. Low voltage control of remote equipment

iii. Isolation of control circuit from load circuit.

iv. Switching.

For this project an electromagnetic relay is used with the function of switching. It has two terminal

normally closed and normally Opened.

2.13 LIGHT DEPENDENT RESISTOR

LDRs or Light dependent resistors are very useful especially in light/dark sensor circuits.

Normally the resistance of an LDR is very high, sometimes as high as 1000000 ohms, but when

they are illuminated with light resistance drops dramatically. Electronic sensors are the devices

that alter their electrical characteristics in the presence of visible or invisible light.

Figure 2.9: Symbol of an electromagnetic relay

19

Figure 2.10: Light Dependent Resistor

The darkness falling on the brown zigzag lines on the sensor causes the resistance of the device to

fall. This is known as a positive co-efficient. There are some LDRs that work in the opposite way

i.e. their resistance decreases with light (called negative co-efficient).

2.14 CONCLUSION

This chapter showed a review of the various components used in the process of construction, their

various operating principles and mechanism of operation. The various advancement in the each

stage of development and the gain associated with each process of development will be presented

in the next chapter.

20

CHAPTER THREE

DESIGN AND ANALYSIS

3.1 INTRODUCTION

This chapter will present the calculation for the design parameter before selection of the

components involved in the coupling of the entire device. This chapter has emphasis on hardware

design and it involves specifying the values and ratings of all electrical/electronic components and

also how they are to be connected.

3.2 FILTER

Before selecting the dropping capacitor, C1 it is necessary to understand the working principle and

operation of the dropping capacitor C1. The X rated capacitor is designed for 250, 400, 600 VAC.

Higher voltage versions are also available. The Effective Impedance Z, Reactance X and the Mains

frequency (50 – 60 Hz) are the important parameters to be considered while selecting the capacitor.

The capacitor should have the ability to filter all ripples and it is expressed as the equation below

γ = 1

4√3 fcR1

… (3.1)

𝛾 = ripple factor

F = frequency

C = capacitor

𝑅1 = bleeder resistor

Choosing a ripple factor of 1% 𝛾 = 0.01

21

C = 1

4√3 𝑓 𝛾 𝑅1

… (3.2)

C = 1

4√3 × 50 × 0.01 × 1 × 106

C = 0.28 × 10−6F

C1 = 0.47μF 400V (chosen)

C1 is the non-polar high voltage capacitor which is introduced for dropping the lethal mains current

to the desired limit.

The reactance X of the capacitor C in the mains frequency f can be calculated using the formula

X = 1

2πfc1 … (3.3)

let f = 50Hz

X = 1

2π x 50 x 0.47x 10−6

X = 6772.5Ω

Effective impedance Z of the capacitor is determined by taking the load resistance RL as an

important parameter. Impedance can be calculated using the formula

Z = RL + X … (3.4)

Suppose the current in the circuit is I and capacitor voltage C1 is 400V then the equation appears

like

I = VC1

X … (3.5)

22

The final equation thus becomes

I = 400

6773

= 59mA

With 0.47μF, 400V will deliver a current of 59mA without load.

Capacitor C2 is chosen to be 470μF 50V which perform the function of filtration

Figure 3.1: Circuit diagram of the photocell power supply

3.3 IN-RUSH LIMITING CURRENT RESISTOR

R1 is bleeder resistor chosen to be 1MΩ it has the function of removing stored current in AC when

power is off.

R2 is in-rush limiting current resistor chosen to be 470Ω which may be optional but is

recommended for tackling a switch ON surge from mains.

23

3.4 RECTIFICATION

A rectifier is a circuit which employs the use of one or more diodes to convert alternating current

into pulsating direct current voltage. The full wave bridge rectifier is to be used in this project

which consist of four IN4007. When selecting a rectifier, the peak inverse voltage PIV is

considered. The peak inverse voltage is the maximum voltage that occurs across the rectifying

diode in the reverse direction

PIV = 2Vmax … (3.6)

Vrms = 12V

Vmax = Vrms × √2 … (3.7)

From 3.4

Vmax = 12 × √2 = 16.97V

From3.3

PIV = 2 × 16.97 = 33.9V

The peak value of current that the diode must be able to pass safely with resistance load is I peak.

Ipeak = π

2 × Idc … (3.8)

= π

2 × 59 × 10−3 = 0.0927A

Diode D1-D4 is chosen to be IN4007 3A/100V with the function of converting ac voltages to dc

voltages and because it has a voltage tolerance of 1000volts.

24

3.5 VOLTAGE REGULATION

Zener diode is used to generate a regulated DC output and it is designed to operate in the reverse

breakdown region. If a silicon diode is reverse biased, a point reaches where its reverse current

suddenly increases.

Zener diode ZD1 is chosen to be 12V which perform the function of voltage regulation to 12Vdc.

3.6 THE SENSING CIRCUIT

The sensor is a light dependent resistor (LDR), with light the resistance increases up to 10MΩ

while with the absence of light the LDR resistance reduces.

Going through data books Q1, Q2 and Q3 were chosen to be BC547, it has the following

characteristics.

Collector-Base Voltage VCBO = 60V

Collector-Emitter Voltage VCEO = 45V

Emitter- Base Voltage VEBO = 6V

Collector Current IC (DC) = 100mA

DC Current Gain hFE min = 100

fT (max) = 150MHZ

Pout (max) = 300mW

VBE Silicon = 0.7V.

VBE (ON) = Base Emitter ON voltage = 1V max,

25

Figure 3.2: Circuit diagram of sensor circuit

The present of light ray reduces the LDR resistance and allows current to pass to the biasing

resistors, which form a potential divider.

Let LDR resistance = RLDR

Let RX be the total series resistance between RLDR and R1

Rx = RLDR + R3

RB1 =(RX × VR1)

(RX + VR1)

At the base circuit of Q1 assuming the presence of light:

VCC = VX + VBE1

where VX is the voltage at RLDR and R3

12 = VX + 0.7

VX = 11.3V

26

Also, V3 = I3R3 and

RB1 = R3 × VR1

R3 + VR1

Where: RB1 is base resistance of Q1

Ib1 = Ic1

hfe1 … (3.9)

At the collector circuit of Q1

Vcc = I4R4 + Vce1 … (3.10)

From characteristic table

Ic1 =10mA and hfe1 (min) = 110 from datasheet

Then, Ib1 = 10mA

110

Ib1 = 0.1mA

Rb1 = Vb1

Ib1 … (3.11)

IX = IVR1 + Ib1 . . . (3.12)

But IVR1 = 10% IC1

IVR1 = 0.1 × 0.01

IVR1 = 1mA

Ix = 0.001 + 0.0001

IX = 1.1mA

27

Since Vx = 11.3

RX = 11.3

0.0011

RX = 10,272Ω (prefer value is 10KΩ) Because it is the nearest available value in the market.

But RX = RLDR + R3

Assume R3 = 1KΩ then,

RLDR = RX − R3

RLDR = (10 − 1)KΩ

RLDR = 9KΩ when no light is focusing the LDR

VR1 = VVR1

IVR1

VR1 = 0.7

0.001

VR1 = 700Ω, hence 10KΩ was chosen and preset to 700Ω

Similarly, at the collector circuit of Q1, (when Q1 is conducting)

VCC = V4 + Vce1

VCC = V4 + Vce1

VCC = 12V

12 = I4R4 + Vce1

Generally VCE is 1

3 of VCC

28

12 × 1

3 = 4V

Vce1 = 4V

VCC = I4R4 + Vce1

12 = I4R4 + 4

8 = I4R4

R4 = 8

I4

But I4 = IC1 = 10mA (chosen value)

R4 = 8

0.01

R4 = 800Ω

We choose a value of 1KΩ for R4

When Q1 is conducting Q2 will not be conducting but when Q1 is not conducting then Q2 will be

conducting

At the base circuit of Q2 note Q2 is also BC547, (when Q1 is not conducting)

VCC = V4 + V5 + Vbe2

12 = 3 + V5 + 0.7

V5 = 8.3V

V5 = I5R5

29

I5 = Ib2

Ic2 = 10mA refer to datasheet

hfe2 = 110

Hence, I4 = Ib2 = Ic2

hfe2

I5 = 0.01

110

I5 = 0.1mA (approximately)

I5 = 0.1mA

R4 = V4

I4

R5 = 8.3

0.0001

R5 = 6.5KΩ

At the collector circuit when Q2 is conducting that is when darkness is on the LDR

VCC = V5 + Vce2

VCC = V5 + Vce2

VCC = 12V

12 = V5 + Vce2

In general VCE should be 1

3 of VCC (this allows for maximum undistorted voltage swing when there is

capacitive coupled a.c. load).

30

Vce2 = 4V (approximately)

V5 = 12 − 4

V5 = I5R5

But I5 = Ic2 = 8mA

R5 = V5

I5

R5 = 8

0.008

R5 = 1KΩ

At the collector circuit of Q2, when Q2 is conducting

VCC = IL1RR1 + VCe1

Vce3 = 1

3 of Vcc

VCC = 12V

Vce1 = 4V

Rr = Relay resistance

IL = collector current

12 = IL1RR1 + 4

IL1RR1 = 8V

IL1 = IC2 and was chosen to be 20mA as collector current Q3

31

RR1 = 8

0.02

RR1 = 400Ω

Hence, the Relay JZC-20F with 12V DC, 10A-and 400Ω characteristic was chosen.

D1 is a freewheeling diode it has the function of protecting Q2 from any excessive current from

the relay. D1 was chosen to be IN4001.

3.7 POWER SUPPLY

Ib = P

V … (3.13)

Ib=

100230

= 0.44A

3.8 PROTECTIVE UNIT (CIRCUIT BREAKER)

We select a type B 10Amperes single throw 3 phase circuit breaker giving allowance for additional

lighting greater than or equal to design current IB

3.9 THERMAL CONSTRAINT

3.10 CABLE SELECTION

Since it is going to be installed in an area where heat and environmental condition will not allow

the cable to cool, correction factor will be required.

Tabulated current capacity of the selected cable

It = In

Ca × Cg × Ci × CC … (3.14)

32

Where;

Ca = Correction factor for ambient temperature

Cg = Correction factor for grouping of cables

Ci = Correction factor for thermal insulation

CC = Correction factor for protective device

= 10

0.94 × 0.88 × 0.82 × 0.725

= 20.33𝐴

3.11 VOLTAGE DROP

Voltage drop = (mv A m⁄⁄ ) × IB × L

1000 … (3.15)

Where;

mv/A/m is millivolt/ampere/metre

IB is the load current

L is the length of the circuit

1000 is the conversion factor for 1 millivolt

For a 4mm2 line conductor and circuit protective conductor of 1.5mm2 is equal to resistance per

meter of copper to be

Voltage drop =16.71 × 10 × 0.44

1000

= 0.07V

33

The resistance of the cable at operating temperature of 70oC

R = (r1 + r2) × length in mΩ

1000 … (3.16)

r1 + r2 = 16.71

= 16.71 × 10

1000

= 0.167Ω

≈ 0.2Ω

3.12 EARTH FAULT LOOP IMPEDANCE

The resistance of the cable at operating temperature of 70oC is 0.2 Ω

Earth loop impedance Zs must now be calculated

Zs = Ze + (r1 + r2) … (3.17)

Where;

ZS = total loop impedance

Ze = loop impedance external to the installation

R1 = resistance of the phase conductor

R2 = resistance of the circuit protective conductor

where Ze = 0.7Ω

Zs = 0.7 + 0.2

= 0.9Ω

34

Zs provides a disconnection time for a circuit breaker of 10A and the maximum disconnection

time is 3.71seconds

3.13 RESISTANCE OF THE CABLE

The resistance of the cable can be determined from the following expression below

R = ρl

A … (3.18)

Where;

ρ = resistivity of the electrical conductor (copper)

l = length of the cable

A = cross sectional area of the conductor

R = total resistance

To determine the resistance of 10m of 4mm copper cable. Given that the resistivity of copper is

1.78 x 10-8 Ω

R = 1.78 × 10−8 × 10

4 × 10−6

= 0.0267Ω

3.14 AREA OF CABLE

The cross sectional area of the cable can be computed from the following expression as stated

below

Area A = ρl

R … (3.19)

35

= 1.78 × 10−8 × 6

0.0267 × 10−6

= 4mm2

3.15 TRUNKING

Any cables installed into a trunking or duct should not use more than 45% of the available space

within the trunking or duct.

For a 40𝑚𝑚 × 25𝑚𝑚 trunking of usable cross-sectional area can be found by

40mm × 25mm = 1000mm2

45% of the area can be found

45

100 × 1000mm = 450mm2

Maximum number of 4mm2 cable that can fit into a 40 x 25mm trunking allowing for space factor

Amount of allowable space that can be used in the trunking = 450mm2

From table A, the diameter overall of a 4mm2 cable is 4.3mm2.

The cross-sectional area of the cable

𝐴 =Πd2

4 … (3.20)

Where;

d is the diameter of the conductor

A is the cross-sectional area

A = π × 4.32

4

36

= 14.52mm2

To calculate the number of cables that is permissible in a trunking

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑎𝑏𝑙𝑒𝑠 = 𝑢𝑠𝑎𝑏𝑙𝑒 𝑎𝑟𝑒𝑎

𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓𝑡ℎ𝑒 𝑐𝑎𝑏𝑙𝑒 … (3.21)

= 450

14.52

= 30 cables

To calculate the number of streetlights that can be powered by one unit of the automatic lighting

switch.

For ease of understanding we are going to be using a single phase supply voltage for our calculation

Vsupply = 230V

𝑁𝑜𝑚𝑖𝑛𝑎𝑙 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝐼𝑛 = 10𝐴

In the case of this project, all Calculations are going to be made without diversity, since all the

lightings are going to be assumed to be on at the same time since the model is a streetlight.

For a 100Watts energy saving bulb;

Current demand for each bulb Idemand = 𝑃𝑏𝑢𝑙𝑏

𝑉𝑏𝑢𝑙𝑏

= 100𝑤

230

=0.44𝐴

Total number of bulbs that can be used with one unit of automatic lighting switch

37

=Irated

Idemand

Where;

Irated = nominal current of the protective device

Idemand = load current

=10

0.44

=22.7

≈ 22 𝑔𝑖𝑣𝑖𝑛𝑔 𝑎𝑙𝑙𝑜𝑤𝑎𝑛𝑐𝑒 𝑓𝑜𝑟 𝑠𝑡𝑎𝑟𝑡𝑖𝑛𝑔 𝑠𝑒𝑞𝑢𝑒𝑛𝑐𝑖𝑛𝑔

3.16 ENERGY CONSUMPTION CALCULATION

Since we are trying to minimize energy waste, we are going to calculate the difference between

using an automatic switch and a manual switch

Supply Voltage = 230V

Current = 10A

Number of hours in a day = 24hrs

Number of days in a month = 30days

Number of months in a year = 12months

The energy E in Kilowatt-hours (kWh) per day is equal to the power P in watts (w) times number

of usage hours per day (t) divided by 1000 watts per kilowatt.

E (kwh

day) =

P(w) x T(h/day)

1000(w/kw) … (3.22)

38

Where parameters above are defined as;

E = Energy

P = Power in watts

T = Time in hours/days/months

1000 = Conversion factor for 1 kilowatt

3.17 POWER CONSUMPTION IN 24 HOURS FOR LIGHTING WITHOUT

PHOTOCELL

Power Consumption = 230 x 10 = 2300w

Hours of use per day = 24hrs/day

Energy consumed per day = 2300 x 24

1000

= 55.2 Kwh/day

Energy consumed per month = 55.2 x 30

= 1656Kwh/month

Energy Consumed per year = 1656 x 12

= 20148Kwh/year

3.18 POWER CONSUMPTION FOR ESTIMATED 11-HOURS USING PHOTOCELL

Power Consumption = 230 x 10 = 2300w

Hours of use per day = 11hrs/day

Energy consumed per day = 2300 x 11

1000

39

= 25.3Kwh/day

Energy consumed per month = 25.3 x 30

= 759Kwh/month

Energy consumed per year = 759 x 12

= 9108Kwh/year

3.19 YEARLY POWER GAINED AS A RESULT OF THE AUTOMATIC SWITCHING

The yearly power gained, YPG of the automatic switch can be computed using the expression

below;

YPG = YP24 − YP11 … (3.23)

Where;

YP24 = Total yearly power used in 24hrs duration

YP11 = Total yearly power used in 11hrs duration

YPG = 20148 − 9108

` = 11040 Kwh/year

3.20 CONCLUSION

This chapter has presented in detail the analysis and calculation of all components before the

implementation of the construction for optimum performance of the system based, the required

value of component chosen was indicated.

40

The next chapter will present the procedures undertaken in constructing the system and the testing

result showing the performance of the system coupled with a reliability test showing that the

efficiency of the system is high and capable of functioning for a long duration of time.

41

CHAPTER FOUR

CONSTRUCTION AND TESTING

4.1 INTRODUCTION

This chapter will present the construction procedure and testing involved in this project. The

ultimate aim of a design process is to realize the physical system where construction is the

assembling and connection of the individual devices electrically as specified by the design which

makes the product of the construction process a working version of the system. Testing is very

vital in engineering, it matches the developed product against the specification to verify that what

was proposed has been achieved. The system tests would be carried out in a step-wise approach

that is from the power aspect to the signal aspect before the general system testing. If the results is

successful, a reliability assessment of the system will be presented.

Construction was conducted in order to put together all the components discussed in the

previous chapters to form a single circuit of the entire project. This chapter discuss in detail

about the circuit construction material, construction procedure.

4.2 CONSTRUCTION

4.3 COMPONENTS USED FOR CONSTRUCTION

The following components were used in the construction of this project:

1. Cables

2. Connectors

3. Contactor

4. Auxiliary contactor

5. Rotary switch

6. Circuit breaker

42

7. All associated electronic components

4.4 CONSTRUCTION MATERIALS

The materials used while constructing this project include, testing board, vero board, soldering

iron, soldering lead wire, sucker and flexible wires i.e. jumpers.

VERO BOARD – is made up of a thin sheet limited insulating material manufactured with

regular spaced holes permit mounting of electronics used as a permanent board on which the

circuit was constructed.

TEST BOARD – is a special board made for testing the circuit before mounting the component

onto a vero board for construction and soldering. The components were not soldered on the

test board but rather tighten holes conductors are used to provide easiness of connection.

SOLDERING IRON – is the material used to heat the lead wire between the conductors and

connecting point on the vero board.

SOLDERING LEAD WIRE – this is the material used as means of connection between

conductor and the board by applying heated soldering iron.

SUCKER – is a material used to removed excess lead wire at the soldered joint or when

removing component i.e. to suck out the lead wire away from the terminal.

JUMPERS – these are wires that are used when connecting two or more terminals of the

component together.

4.5 CONSTRUCTION PROCEDURE

Before assembling the components into a circuit board, a test board was initially used to test

whether all the components arranged could perform the expected function. The construction

procedures are as stated below:

43

1. All the required components were tested using digital multi-meter so as to confirm its

functionality before it was taken to the circuit for soldering.

2. The components were plugged in vertically in the position specified in the circuit

connection and vero board conductors arrangement, also flexible wires were used where

necessary.

3. The components were soldered on the board using soldering iron and soldering lead wire.

4. The soldered connections were tested using multimeter and other equipments to ensure

efficient soldering.

4.6 TESTING

Based on the fact that no engineering work could be done without testing. Before the testing

of the whole circuit, testing of individual components was undertaken and this test was

conducted by using a digital multi-meter.

4.7 RELIABILITY TEST

Reliability test was also carried out on this project. This is a characteristic of the system

expressed as the probability of that system to perform a required function under stated conditions

for a stated period of time. Reliability is obtained by the use of a formula.

𝑅 = 𝑒−λt … (4.1)

Where:

R is the reliability of a system

λ Is the rate (%/103 hours)

4.8 ASSESSEMENT OF EQUIPMENT/SYSTEM RELIABILITY

The following steps are the procedure for reliability assessment;

44

1. List the components parts of the equipment/system.

2. State the failure rate of each part.

3. Multiply by the number of similar parts.

4. Multiply by all the available weighing factors.

5. Add-up all the products obtained from steps (2) through to (4) to give the overall failure rate

(λ) for the equipment/system.

6. Determine the equipment/system reliability for a given operating period using the equation

𝑅 = 𝑒−λt … (4.2)

Table 4.1: Reliability of the individual component used.

Component Number

Used

Basic failure

i 𝛌 rate,

hours)3(%/10

Weighting

factor due to

environment,

We

Weighting

factor due to

temp, Wt

Weighting

factor due

to rating.

Wr

Overall

failure

rate,

λoi

Resistor 7 0.005 1.0 1.5 2.0 0.035

Capacitor 2 0.02 1.0 1.5 6.0 0.04

Oscillator 1 0.004 1.0 1.5 1.0 0.004

Diodes 6 0.01 1.0 1.5 - 0.06

Transistor 2 0.08 1.0 1.5 1.0 0.16

LED 2 0.05 1.0 1.5 1.5 0.1

Relay 1 0.09 1.0 1.5 1.5 0.09

LDR 1 0.8 1.0 1.5 1.0 0.8

Connections 50 0.001 1.0 1.5 1.0 0.050

Soldering 42 0.001 1.0 1.5 1.0 0.042

45

The overall failure rate of the system is the summation of the failure rates, λoi given by

∑ 𝜆𝑜𝑖 = 𝜆𝑇 = 0.035 + 0.04 + 0.004 + 0.06 + 0.16 + 0.1 + 0.09 + 0.8 + 0.050 + 0.042

= 1.381% 1000ℎ𝑜𝑢𝑟𝑠⁄

For an operating time of one year, that is 365 days

𝑡 = 24ℎ𝑜𝑢𝑟𝑠 × 365 = 8760 ℎ𝑜𝑢𝑟𝑠

∴Failure rate of the device for a year,

ƛ𝑇 × 𝑡 = 1.381%

1000ℎ𝑜𝑢𝑟𝑠 × 8760

=1.381

100×

1

1000×

8760

1

= 0.12097

∴ The reliability of the system is calculated below

𝑅 (𝑡) = (−𝜆𝑡) … (4.3)

= (−0.12097)

= 0.886

= 88.6%

Therefore the reliability of the system is 88.6 0/0 which shows that the system is reliable.

4.9 CASING OF THE PROJECT

The control circuit was purchase in the market, though the dimensions were calculated before

its purchase.

46

Where

H = height

W = width

L = length

H = 29cm, W = 16 cm and L = 19cm

The cuboid was used to determine surface area and volume

Surface Area (A) = 2(𝐿𝑊 + 𝐿𝐻 + 𝐻𝑊) … (4.4)

= 2((19 × 16) + (19 × 29) + (29 × 16))

= 2(304 + 551 + 464)

= 2638𝐶𝑚2

Total Volume (𝑉) = 𝐿𝑊𝐻 … (4.5)

= 19 × 16 × 29

= 8816𝑐𝑚3

Note, for installation of the indicator lamps and rotary switch, adjustment were made to

the casing to house them.

H

L

W

Figure 4.1: Casing

47

4.10 RESULTS

After construction was carried out, the constructed circuit was satisfied okay and testing of

the project was done after all safety precautions were observed.

Table 4.2: Results of the 3-phase LDR automatic switch

Main power Power indicator LDR Street light Green indicator

Off Off Darkness on it Off Off

Off Off Light on it Off Off

On On Darkness on it On On

On On Light on it Off Off

Multi-meter was used to test the output of the power supply circuit and a constant

220/415Vac was obtained, also during testing all safety conditions were observed.

4.11 DISCUSSION OF RESULTS

Based on the test carried out, it was found that the response time of the photocell sensor is a little

bit different from what is expected having approximately 1 second difference and as seen from the

table the expected response of the system was achieved. The difference in the sensitivity of the

device is mainly as a result of two major factors as indicated by the manufacturer data sheet; the

variable resistor settings of the LDR sensor and also environmental conditions including ambient

temperature and light source. This shows the system is best suited for outdoor use.

The state of the device when energized was seen to give reasonable working values as shown in

the observed results. Also considering the system reliability assuming the system is operating at

night for 11hours every day, it shows that the system is highly reliable having a reliability of 88.6%

48

4.12 PRINCIPLE OF OPERATION

When the light level is low the resistance of the LDR becomes low allowing current to flow

through R3 to the base of the transistors as shown in Figure 4.2. With continuous decrease in light

level R3 is the biasing resistor to Q1 with a bias voltage of 0.7V at the base of Q1 then Q1 will be

in conduction which in turn will bias the NPN transistor BC547 Q2.

Similarly, at the emitter of Q1 and base of Q2 a voltage built is experience as the decrease in light

increases The emitter of Q1 is connected to the relay which switches between normally open and

normally close to switch on the contactor.

Also from Figure 4.3, relay is implemented so as to oscillate between normally open and normally

closed which is configured to automatically switch on the contactor or to be set at normally closed

so as to bypass the light dependent resistor and provide manual switching function.

The power supply to the photocell circuit is provided by a 220V ac power circuit which is then

rectified by the full wave bridge rectifier to 12V dc and capacitor C2 performs the filtration before

it is transferred to the relay which then gives an output to our ac load (light). The power supply to

the control switchgear.

The initial power 220V ac supplied to the photocell was gotten from the 3phase automatic switch

which is first passed through a circuit breaker to serve as the primary protection device which

protects the circuit from fault current. The contactor serves to make or break the circuit

automatically while signal is transferred from the auxiliary contactor to the indicator lamps to

indicate the state of operation of the circuit.

In constructing this project the circuit was divided into four parts;

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Figure 4.2: Main components of the system

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Figure 4.3: Photocell circuit diagram

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Figure 4.4: Automatic switch circuit diagram

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4.13 SAFETY PRECUATION

1. It was ensured that the circuit was not connected while the power supply is ON.

2. It was ensured that all connections were properly made before connecting the power

supply.

3. Care was taken during the circuit connection to damaging the component to avoid the effect

of short circuit current.

4. It was ensured that test were carried out to ensure that the circuit is free from short and open

circuit.

5. Care was taken while soldering the components to the Vero board so that the heat does not

damage the components.

6. It was ensured that incase of any partial contact or line short circuit, the joint was re-

soldered and the cause of the partial contact was sucked out to clear the short circuit.

4.14 APPLICATIONS OF THE SYSTEM

It can be used in some clocks, alarms, and other electronic devices that are dependent on

sunlight.

We can used it outside of house, corridors or industry area, which helps to save

power.

It can be used as a street light.

In sea off-shore side we can use it as a dangerous sign

4.15 CONCLUSION

The chapter summarizes the tests that were carried out on the hardware of the system as well as

states the problems that were encountered in its development. The reliability test showed that the

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system is sufficiently reliable and the results showed the various task it performed at the end of

the construction.

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CHAPTER FIVE

SUMMARY, CONCLUSION AND RECOMMENDATION

5.1 SUMMARY

This project is intended to design and construction of an LDR-based 3-phase automatic switch in

order to reduce power consumption. The following important considerations were made during the

design and construction of the automatic system; ability of the system to be compatible with a 3-

phase electricity network and also the ability of the system to withstand adverse weather condition

since it is going to be located outdoor. There was a reasonable justification of using this switch

over a manual switch as the long term benefits of the system was shown. To change the switching

from analog to digital the following components were used; contactor, photocell, rotary switch

were all implemented to essentially provide control of the system. Basically, the sensor which is

connected to the contactor senses light intensity and switch the contactor to either switch on or off

the load attached to it.

The designed system has managed to solve the problems faced due to the inappropriate switching

time by using the automatic system, there are a few issues in the new systems which can be solved

with further improvements.

5.2 CONCLUSION

This paper elaborates the design and construction of automatic light control system. The circuit

works properly to automatically turn lamp ON/OFF. LDR sensor is the main conditions in

working the circuit. If the conditions have been satisfied the circuit will do the desired work

according to the signal from the sensor. The sensor controls the turning ON or OFF of the

lighting. With commands from the contactor, the lights will be ON when it sense darkness in

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a particular environment. Finally this control system can be used in various purposes.

5.3 RECOMMENDATIONS FOR FUTURE SCOPE OF WORK

Automatic light are expensive in comparison to normal switch but can return the investment in a

short duration as the lifetime of equipment will be prolonged and there will be reduced wastage

of power.

For the above project we can develop solar street light system with Automatic street light

controller. The system can be powered from a battery, which can be charged during day time

by harvesting the solar energy through a solar cell. The solar energy harvested from sunlight

can be stored, inverted from dc voltages to ac voltage using a dc to ac converter.

The above mentioned strategy will enable us to harvest solar energy in an effective way for

the operation of the circuit and for powering the street light.

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5.4 REFERENCES

[1] Oladeji, A. (2008): “Impact of power consumption to industrialization in Nigeria’’, Second

Edition, First Publishers, Lagos, Nigeria p. 28.

[2] DiLouie, C. (2008): “Lighting controls handbook”, First Edition, Fairmont Press. Lilburn,

Ga, p. 239.

[3] Terrell, C., and Wilford S. (1987): “American Electricians Handbook”, Eleventh Edition,

McGraw Hill, New York, page 121-124.

[4] Rajput K.Y., Khatav G., Pujari M., Yadav P., (2013): “Intelligent Street Lighting System

Using Gsm”, Volume 2 Issue 3, International Journal of Engineering Science Invention,

Delhi, PP. 60- 69.

[5] Devi, D. A. and Kumar, A. (2012): “Design and Implementation of CPLD based Solar

Power Saving System for Street Lights and Automatic Traffic Controller”, Vol. 2, Issue

11, International Journal of Scientific and Research Publications, PP. 5-15.

[6] Sudhakar, K. S., Anil, A. A., Ashok, K. C. and S. S. Bhaskar, (2013): “Automatic Street

Light Control System”, Vol. 3, International Journal of Emerging Technology and

Advanced Engineering, Kuala lumpur, PP. 188-189.

[7] Wazed, M. A., Nafis, N. M., Islam, T. and Sayem, A. S. M., ( 2010): “ Design and

Fabrication of Automatic Street Light Control System, Engineering e-Transaction”, Vol.

5, No. 1, Daffodil International University PP 27-34.

[8] Diffenderfes, R., (2005): “Electronic Devices: System and Applications”, Third Edition,

Delimar publishers, New Delhi, PP 480.

[9] Rashid M. H., (2008): “Power Electronics circuits, devices and applications”, Third

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Edition, Lead publishers, Manchester, PP 20 – 75.

[10] Boylestad R. & Nashelsky L., (2009): “Electronic Devices and Circuit Theory”, Seventh

Edition, Prentice Hall Publishers, New Jersey, PP 27 – 97.