i

AUTOMATIC EARTH LEAKAGE CIRCUIT BREAKER WITH BACKUP

SUPPLY

MOHD ANUAR BIN MOHAMED AYUB

A project report submitted in partial fulfillment of the

Requirement for the award of the

Master of Electrical engineering

Faculty of Electrical and Electronic Engineering

Universiti Tun Hussein Onn Malaysia

DECEMBER 2013

v

ABSTRACT

Power system protection is the most important requirement in the industrial or domestic

electrical to prevent equipment from damage cause by leakage current. The ELCB is an

important equipment to install at each of house, hospital, factory, or every place that need the

power supply. The device monitors input current from power line by using the sensor Zero phase

Current Transformer (ZCT), and then send the signals to the mechanical switch to tripped the

circuit breaker. Industrial operation requires protection of their equipment from the lightning

short circuit and also over-current, thus the ELCB will serve the purpose as the protection of

their system .This research will attempt to improve the exciting ELCB design using PIC

microcontroller to automatically switch it back to normal when the ELCB tripped in home during

instantaneous over current or short circuit. This system provides a convenient way for house’s

owner especially during absences in home. In this research PIC 16F877A microcontroller is used

to control overall flow operation and operate the Power Relay /Protection relay, thus replacing

the current mechanical switch. The outcome of this research after several testing process shown

that the average sensitivity value for ELCB against leakage current is 76mA better 24% than

100mA set by manufacture.

vi

ABSTRAK

Perlindungan sistem kuasa adalah keperluan yang paling penting di dalam indusrtri

ataupun sambungan domestic elektrikal bagi mengelakan kerosakan peralatan

disebabkan oleh arus bocor . ELCB adalah salah satu peralatan penting yang di pasang di

setiap rumah , hospital, kilang ataupun tempat yang memerlukan bekalan kuasa.

Peralatan ini bertindak sebagai pemerhati arus masukan dari talian kuasa oleh pengesan

Pengubah Tanpa Arus Fasa (ZCT), kemudianya ia menghantar isyarat tersebut ke suis

mekanikal untuk terpelantikkan pemutus litar.Operasi industri memerlukan perlindungan

mesin mereka daripada kilat, litar pintas dan juga lebihan arus, maka ELCB ini akan di

gunakan bagi perlindungan kepada sistem mereka. Projek ini adalah bertujuan untuk

menambahbaikan rekabentuk ELCB yang sedia ada menggunakan PIC pengawal mikro

untuk menyambung kembali litar ELCB yang telah terpelantik kepada keadaan asal

apabila berlakunya litar pintas dan lebihan arus. Sistem ini memberikan manfaat kepada

pemilik rumah apabila tiada di rumah. Didalam projek ini PIC16F877A pengawal di

gunakan untuk mengawal keseluruhan sistem pengoperasian dan Geganti Kuasa/Geganti

Perlindungan yang mana telah di tukarkan kepada suis mekanikal asal. Hasil di akhir

projek ini, setelah beberapa kali di uji didapati kepekaan ELCB terhadap arus bocor

adalah 76mA di mana 24% lebih baik daripada 100mA telah ditetapkan oleh pembuat.

vii

TABLE OF CONTENTS

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABCTRACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLE xi

LIST OF FIGURE xii

LIST OF ABBREVIATION xv

LIST OF APPENDIXES xvi

CHAPTER 1 INTRODUCTION 1

1.1 Project Background 1

1.2 Objectives 2

1.3 Scopes of Project 3

1.4 Problem Statement 3

CHAPTER 2 LITERATURE REVIEW 4

2.1 Introduction 4

2.2 Earth Leakage Circuit Breaker (ELCB) 5

2.2.1 Voltage Earth Leakage Circuit Breaker (vELCB) 7

viii

2.2.2 Current Earth Leakage Circuit Breaker (iELCB) 8

2.3 Operation of ELCB Trip Situation 8

2.3.1 Permanent Failure or Permanent Damage 8

2.3.2 Temporary Failure or Temporary Damage 9

2.4 Electrical Faults 9

2.4.1 Over-current Fault 9

2.4.2 Short Circuit Fault 10

2.4.3 Lightning Fault 10

2.5 ELCB Features 11

2.6 ELCB Design 12

2.7 Basic Concept of ELCB 14

2.8 Operation of ELCB 15

2.9 Conclusion for previous report 16

CHAPTER 3 METHODOLOGY 18

3.1 Introduction 18

3.2 Planning 19

3.2.1 Phase 1 : Preliminary Investigation 20

3.2.2 Phase 2 : Analysis and Specification 20

3.2.3 Phase 3 : Design 20

3.2.4 Phase 4 : Development and Integration 20

3.2.5 Phase 5 : Testing 21

3.2.6 Phase 6 : Maintenance 21

3.3 Hardware Development (Research Requirement) 21

3.3.1 ELCB Hardware Design 21

3.3.2 ELCB with an Automatic Unit Hardware Design 22

ix

3.3.3 UPS Configuration 23

3.3.3.1 Standby or off-line system 24

3.3.3.2 Double conversion on-line system 24

3.3.3.3 Line interactive system 25

3.4 Hardware Operation Process 26

3.5 Circuit Stage 28

3.5.1 Voltage Regulator Circuit 28

3.5.2 PIC Microcontroller and LCD circuit 29

3.5.3 Relay Driver Circuit 30

3.5.4 Final Stage Circuit 31

3.6 ELCB Hardware Part 32

3.7 Overall System 33

3.8 Hardware and Software Development 34

3.8.1 PIC16F877A 34

3.8.2 Relay 240 Volt 35

3.8.3 Relay Driver 36

3.8.4 Current Sensor 37

3.8.5 MPLAB 38

3.8.6 PROTEUS 39

CHAPTER 4 RESULT AND ANALYSIS 40

4.1 Hardware Result 40

4.1.1 Power Supply Circuit 40

4.1.2 LCD Display 42

4.1.3 Protective Relay 47

4.1.4 Wiring Diagram Of ELCB And Protective Relay 51

4.2 Analysis 53

x

4.2.1 Normal Condition 53

4.2.2 Second Condition: Main Trip 54

4.2.3 Third Condition: Backup Trip 56

4.2.4 Calculation Percentage Between Theories with 62

The Actual voltage

4.2.5 ELCB Test Using Relay Test Unit 62

4.2.6 Calculation Percentage Current 65

Between Manufacturer Rating With

Current Measured By Relay Test Unit

4.2.7 Current During Normal And Backup ELCB Trip 66

4.2.8 Calculation Percentage Current Between 70

Ammeter and LCD display

4.2.9 Overall Discussion 70

CHAPTER 5 CONCLUSION AND RECOMMENDATION 72

5.1 Conclusion 70

5.2 Future Recommendation 73

REFFERENCES 74

APPENDICES 76

xi

LIST OF TABLES

4.1 Input Voltage For Prototype 41

4.2 Input And Output For ELCB And LCD Display 42

4.3 Current During Normal And Main Trip 44

4.4 Condition Of Relay 48

4.5 Normal Condition (No Trip) 58

4.6 Second Condition (Main Trip) 58

4.7 Third Condition (Backup Trip) 58

4.8 Result For ELCB Test 64

4.9 Current During Normal And Backup ELCB Trip 68

xii

LIST OF FIGURES

2.1 TT Network 6

2.2 Home ELCB/RCCB With Housing 11

2.3 The System Inside ELCB 11

2.4 Earth Leakage Circuit Breaker Design 12

2.5 Earth Leakage Circuit Breaker Design Schematic 13

2.6 Operation of ZCT 14

2.7 Earth Leakage Circuit Breaker Operation Flow 15

2.9 Conclusion For Previous Report 16

3.1 Flowchart of Planning 19

3.2 Component and Structure of ELCB 22

3.3 Component and Structure of ELCB with an Automatic Unit 23

3.4 Off-line System Diagram 24

3.5 Double Conversion On-line System Diagram 25

3.6 Line Interactive System Diagram 25

3.7 Hardware Operation Process of Automatic ELCB 28

xiii

3.8 Voltage Regulator Circuit 28

3.9 PIC Microcontroller and LCD Circuit 29

3.10 Relay Driver 30

3.11 Final Stage Circuit For ELCB Control 31

3.12 Final Stage Main Circuit Current Sensor 32

3.13 ELCB Hardware Part 33

3.14 Flowchart of Overall System 34

3.15 The PIC Microcontroller Board 35

3.16 Relay 240 Volt 36

3.17 Relay Driver 37

4.1 Voltage Regulator Circuit With Input 12V And Output 5V 41

4.2 Display on LCD at Normal Condition 43

4.3 Display on LCD at Main Fault Condition 43

4.4 Display on LCD at Backup Tripped 44

4.5 Display On LCD At Current L1 45

4.6 Ammeter Display Current At L1 45

4.7 Display On LCD At Current L2 46

4.8 Ammeter Display Current At L2 46

4.9 Protective Relay for Switching 47

4.10 Relay Driver Circuit Diagram 48

xiv

4.11 Normal Condition 49

4.12 Main Fault Condition 49

4.13 Backup Fault Condition 49

4.14 Wiring Diagram Of ELCB And Protective Relay 52

4.15 Normal Condition 54

4.16 Second Condition of Main Trip 56

4.17 Third Condition of Backup Trip 57

4.18 Normal Condition (No Trip) 59

4.19 Second Condition ( Main Trip) 60

4.20 Third Condition (Backup ELCB Trip) 61

4.21 ELCB Test Using Relay Test Unit 63

4.22 Test ELCB At Current 40mA (No Trip) 63

4.23 Test ELCB At Current 77mA (ELCB Trip) 63

4.24 Result For ELCB Test 64

4.25 Display Current At Load 1 67

4.26 Display Current At Load 2 67

4.27 Result The Current L1 and L2 At Normal Condition 68

4.28 Result The Current L1 And L2 At Backup ELCB Trip 69

xv

LIST OF ABBREVIATION

PIC Programmable Integrated Circuit

ELCB Earth Leakage Circuit Breaker

AELCB Automatic Earth Leakage Circuit Breaker

RCD Residential Current Device

GFCI Ground fault Circuit Interrupted

vELCB Voltage Earth Leakage Circuit Breaker

iELCB Current Earth Leakage Circuit Breaker

ZCT Zero Current Transformer

NO Normally Open

NC Normally Close

LED Light Emitting Diode

xvi

LIST OF APPENDICES

A Gantt Chart 76

B Programming Source Code 80

C Data Sheet 88

CHAPTER 1

INTRODUCTION

1.1 Project background

This project is focused on the design and building a unit of Automatic Earth Leakage

Circuit Breaker (AELCB) with the backup supply that can auto switching and always on

with temporary power supply. Nowadays ELCB is manually controlled by mechanical

switch and have a limited function which are cannot distinguished and notify either

permanent or temporary fault that occurred. An uninterruptible power supply (UPS) or

generator system is a device which provides emergency power and line regulation to

connect equipment by supplying power from a separate source when utility power is not

available. The main focus for this project is to prevent all the critical equipment in the

house system from being breakdown. When the system in the resident will be

disconnected will cause some trouble for the owner to manage the equipment. By using

the UPS or generator system will back up the system urgently whenever the fault and the

tripping occurred and also would rescue or save life of the equipment, especially the

electronic good for example refrigerator, television and laptop in the critical condition.

This may seems unimportant, but if we can solve this problem we can save equipment

life. The new ELCB function does not limited the auto switching [1], but it also can

differentiate and display the type of fault so that the user is aware the situation.

2

There are two types of fault normally detected by ELCB, which are permanent

fault and temporary fault. Permanents fault is type of fault that occurred because of short

circuits between life wire and neutral wire or ground wire, meanwhile temporary fault is

type of fault that occurred from the effect of surge current from the lightning. The

concept is that if faulty occurred, after 10 second, the ELCB will automatically switch

back to normal condition. At the time when that ELCB trip, we will use UPS or

generator as a temporary backup supply. If there is no fault detected after the ELCB is

on, the LCD will display main ELCB in fault condition and backup ELCB is ON. The

ELCB will stay connected until next fault occurred and the counter will be reset. After

PIC counter reach 2, the ELCB will be tripped as to isolated connection of load with

power line. LCD will display backup ELCB in fault condition. In this project the PIC

microcontroller has been chosen as a control and the Power Relay is selected as

switching device.

1.2 Objectives

The objectives of this project are:

i. To investigate the characterization of an Automatic ELCB with automatically

trigger during permanents fault that occur because of short circuit between

life wire with neutral wire and temporary fault is type of fault that occurred

from the effect of surge current from the lightning.

ii. To solve and develop the automatic earth leakage circuit breaker using UPS

or generators system with user monitoring control form of Microcontroller

and power electronic for residential, office and grocery store.

iii. To analysis voltage during the normal condition, second condition (main trip)

and third condition (backup trip) of the automatic earth leakage circuit

breaker in order to determine the proposed system performance.

3

1.3 Scope of project

i. The circuit using mechanism such protective relay to communicate with the

PIC microcontroller to switch on the backup ELCB.

ii. The range for voltage that will cover for this project is limited only 220 to

240V that will be coming from suppliers.

iii. This project focused on the current sensitivity of ZCT in ELCB against

leakage current at normal condition, main trip condition and backup trip

condition.

1.4 Problems Statements

Earth Leakage Circuit Breaker is one type of electrical equipment that used as a

protection device. The main purpose of this type of equipment is to cut off the power

when the problem occurred. The main problem is, if the error occurred and there is no

human that can switch on back the device due to many reasons [1].

The device used is mechanical switch that must be activated manually, after

ELCB is being tripped it will stay off until the user push it back to the ON condition

although the problem that occurred is temporary fault and occurred in one millisecond.

So, it not works as automatic device that can operate automatically.

The worst case scenario, power interruptions can cause the trouble for the

residential system or damage to the house equipments. Loss of power to loads for

example lightning may have serious outcome, resulting in loss of properties and human

lives. The backup power supply is essential in providing the necessary power in the

event of normal supply failure in the building concerned. Under such circumstances, an

interruptible power supply is important.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

ELCB operate by measuring the current balance between two conductors using a

differential current transformer. The device will open its contacts when it detects any

difference in current between the line conductor and the neutral conductor. The supply

and return currents must sum to zero, otherwise there is a leakage of current to

somewhere else (to earth/ground, or to another circuit, etc.)[1].

ELCB is designed to prevent electrocution by detecting the leakage current,

which can be far smaller (typically 5-30 mill amperes) than the currents needed to

operate conventional circuit breakers or fuses (several amperes). RCD (Residential

Current Device) are intended to operate within 25-40 milliseconds, before electric shock

can drive the heart into ventricular fibrillation, the most common cause of death through

electric shock[1].

In the United States, the National Electrical Code requires GFCI (Ground Fault

circuit Interrupter) devices intended to protect people to interrupt the circuit if the

leakage current exceeds a range of 4-6 mA of current (the trip setting is typically 5 mA)

within 25 milliseconds. ELCB devices which protect equipment (not people) are allowed

5

to trip as high as 30 mA of current. In Europe, the commonly used RCD have trip

currents of 10-300 mA[2].

Residual current detection is complementary to over-current detection. Residual

current detection cannot provide protection for overload or short-circuit currents. ELCB

with trip currents as high as 500 mA are sometimes deployed in environments (such as

computing centers) where a lower threshold would carry an unacceptable risk of

accidental trips. These high-current ELCB serve more as an additional fire-safety

protection than as an effective protection against the risks of electrical shocks[2].

For many years, the voltage operated ELCB and the differential current operated

ELCB were both referred to as ELCB because it was a simpler name to remember.

However, the use of a common name for two different devices gave rise to considerable

confusion in the electrical industry. If the wrong type was used on an installation, the

level of protection given could be substantially less than that intended. To remove this

confusion, IEC decided to apply the term Residual Current Device (RCD) to differential

current operated ELCB. Residual current refers to any current over and above the load

current[2].

2.2 Earth Leakage Circuit Breaker (ELCB)

An Earth Leakage Circuit Breaker (ELCB) is a device used to directly detect currents

leaking to earth from an installation and cut the power. It was mainly used in TT

earthing systems. In a TT earthing system, the protective earth connection of the

consumer is provided by a local connection to earth, independent of any earth

connection at the generator[3].

The big advantage of the TT earthing system is the fact that it is clear of high and

low frequency noises that come through the neutral wire from various electrical

equipment connected to it. This is why TT has always been preferable for special

applications like telecommunication sites that benefit from the interference-free

earthing. Also, TT does not have the risk of a broken neutral. In locations where power

6

is distributed overhead and TT is used, installation earth conductors are not at risk

should any overhead distribution conductor be fractured by, say, a fallen tree or

branch[3].

Figure 2.1: TT Network

In pre-RCD era, the TT earthing system was unattractive for general use because

of its worse capability of accepting high currents in case of a live-to-PE short circuit (in

comparison with TN systems). But as residual current devices mitigate this

disadvantage, the TT earthing system becomes attractive for premises where all AC

power circuits are RCD-protected[3].

Nowadays, ELCB have been mostly replaced by residual-current devices (RCD).

The RCD is the current operand ELCB type. Few years ago, there was voltage operand

ELCB, but its utilization was currently had been abolished because it was less effective.

So, the voltage operand ELCB was replaced with the current operand ELCB. The RCD

is an electrical wiring device that disconnects a circuit whenever it detects that the

electric current is not balanced between the phase conductor and the neutral conductor.

Such an imbalance is sometimes caused by current leakage through the body of a person

who is grounded and accidentally touching the energized part of the circuit. A lethal

shock can result from these conditions; RCD are designed to disconnect quickly enough

to mitigate the harm caused by such shocks[4].

7

ELCB has become one of the home safety systems in our life today. ELCB has

reset button which is to reclosed circuit breaker when the tripping occur. Today, many of

people busy with work and usually not at home. The problem are during the over

current, short circuit or current leakage at live conductor, it can trip the circuit breaker

“OFF” and cut off the whole house power supply. This situation can make certain

important component or equipment cannot be operated. Most household ELCB need to

be reclosed manually during tripping, hence is a troublesome thing for user who is not at

home and may be would take long time to reset on back the button at circuit breaker.

The main mechanism in operation is tripping coil which is it can operation either in live

or off condition. This ELCB will operate when current is exceeding the rating of the

current ELCB. This high current not flows into equipment after ELCB tripped. It will

flow directly into ground by using ground rod. This ground rod must has the lower

resistance it because easy to flow high current. There are two types of ELCB[5]:-

i. Voltage Earth Leakage Circuit Breaker (vELCB)

ii. Current Earth Leakage Circuit Breaker (iELCB)

2.2.1 Voltage Earth Leakage Circuit Breaker (vELCB)

vELCB is a voltage operated circuit breaker, the device will function when the current

passes through the ELCB. vELCB contains relay loop which it being connected to the

metallic load body at one end and it is connected to ground wire at the other end. If the

voltage of the load body is rise which could cause the difference between earth and load

body voltage, the danger of electric shock will occur. This voltage difference will

produce an electric current from the load metallic body passes the relay loop and to

earth. When voltage on the load metallic body raised to the danger level which exceed to

50Volt, the flowing current through relay loop could move the relay contact by

disconnecting the supply current to avoid from any danger electric shock[5].

8

2.2.2 Current Earth Leakage Circuit Breaker (iELCB)

iELCB is current operated circuit breaker. Current-operated ELCBs are generally known

today as RCD (residual current device). These also protect against earth leakage,

through the details and method of operation are different. The device will function with

when the Current passes through ELCB. This current admitted to current transform

device and on the load. Current from the load also admitted again to transform device. In

normal state, total current applied to load is equal with total current out of the load.

Because of the balance of in and out of current, it does not affect the current transform

device. If there is any earth current leakage caused by earth damage, then the in and out

current will no longer in balance. This unbalance current phenomenon will generate the

current and if the current exceeded the prescribed rate, the ELCB will jerked and cut off

the supply. The device also being called RCD, Residual Current Device in IEC or

RCCB, Residual Current Circuit Breaker[5].

2.3 Operation of ELCB Trip Situation

There are two types of fault normally detected by ELCB, which are permanent fault and

temporary fault:

2.3.1 Permanent Failure or Permanent Damage

It usually trip when have any leakage current in circuit to earth or ground. For

permanent failure, the damaged must to repair first or remove the damage from current

before automatically trigger back ELCB. If the damage not to repair or remove the

damage from circuit, it will trip again when the ELCB become automatically trigger. If

this happen many times, it will damage the ELCB. For example is electrical, electronic

device or short circuit[6].

9

2.3.2 Temporary Failure or Temporary Damage

It can automatically trigger ELCB without to repairs first or remove the damage from

supply circuit. If usually lightning and over loading occurs in resident or industrial, it

can give more problems to user to automatically trigger by itself. For example is

lightning[6].

2.4 Electrical Faults

A fault is any abnormal situation in an electrical system in which the electrical current

may or may not flow through the intended parts. Equipment failure also attributable to

some defect in the circuit, example is loose connection, insulation failure or short circuit

etc. The type of faults in a distribution network that is detected by an ELCB is[7]:

i. Over-Current Fault

ii. Short-Circuit Fault

iii. Lightning Fault

2.4.1 Over-current Fault

The National Electrical Code defines over current as any current in excess of the rated

current of equipment or the amp city of a conductor. It may result from overload, short

circuit, or ground fault. Current flow in a conductor always generates heat. The greater

the current flow, the hotter the conductor. Excess heat is damaging to electrical

components. For that reason, conductors have a rated continuous current carrying

capacity or amp city. Over current protection devices are used to protect conductors

from excessive current flow. These protective devices are designed to keep the flow of

current in a circuit at a safe level to prevent the circuit conductors from overheating. In

term of over-current fault when a current greater than that which a circuit or a fuse is

10

designed to carry, the fuse or wire may melt or damage the other elements of the

circuit[8].

2.4.2 Short-Circuit Fault

A short circuit in an electrical circuit is one that allows a current to travel a long a

different path from the one originally intended. The electrical opposite of a short circuit

is an “open circuit”, which is an infinite resistance between two nodes. It is an abnormal

low-resistance connection between two nodes of an electrical circuit that are meant to be

at different voltages. This result in an excessive electric current (over-current) and

potentially causes circuit damage, overheating, fire or explosion. Although usually the

result of a fault, there are cases where short circuits are caused intentionally, for

example, for the purpose of voltage-sensing crowbar circuit protectors. In circuit

analysis, the term short circuit is used by analogy to design at a zero-impedance

connection between two nodes. This forces the two nodes to be at the same voltage. In

an ideal short circuit, this means there is no resistance and no voltage drop a cross the

short, in simple circuit analysis, wires are considered to be shorts. In real circuits, the

result is a connection of nearly zero impedance, and almost no resistance[8].

2.4.3 Lightning Fault

Lightning is the visible discharge of static electricity within a cloud, between clouds, or

between the earth and a cloud. Scientists still do not fully understand what causes

lightning, but most experts believe that different kinds of ice interact in a cloud. Updraft

in the clouds separate charges, so that positive charges flow towards the top of the cloud

and the negative charges flow to the bottom of the cloud. When the negative charges

moves downwards, a “stepped leader” is created. The leader rushes toward the earth in

150-foot discrete steps, producing an ionized path in air. The major part of the lightning

discharges current is carried in the return stroke, which flows along the ionized path.

One of the temporary faults is cause by direst lightning phenomena. Where example of

permanent fault is fault on electrical equipment[8].

11

2.5 ELCB Features

Figure 2.2 show about Home ELCB with the housing, the function of this housing as the

protection for the circuit. What who can be seen from this condition is only mechanical

switch and the black box[9].

Figure 2.2: Home ELCB/RCCB With Housing

Figure 2.3 shows the whole ELCB component inside the housing, the most important

thing is the system is the good insulator must be used for live and neutral cable, it is to

avoid from ELCB self fault[9].

Figure 2.3: The System Inside ELCB

12

2.6 ELCB Design

Figure 2.4: Earth Leakage Circuit Breaker design

Figure 2.4 shows the design of ELCB, the design consists of Mechanical Switch, ZCT,

Black Box, High Level Resistor and the Reset Button. Mechanical switch is a contact of

black box, the function of this component is to trigger and cut off the power with cut off

the life and neutral line altogether. The function of high level resistor or test resistor is to

test whether ELCB is operational or not by providing a short circuit within internal

ELCB life and neutral. By providing a new current path during test condition (assuming

Kirchhoff current law), current flow through life wire is divided. The current in the

neutral is less than the current in the life wire when the reset button is pushed. The

function of the reset button is to re-set back the device to the initial condition and also as

a point to detect whether the device still in good condition or damage/expired. The

function of this black box is to induced magnetic and then de-energize the magnetic coil

in the black box[10].

13

Figure 2.5: Earth Leakage Circuit Breaker Design Schematic

Figure 2.5 show the Earth Leakage Circuit Breaker design schematic. The

function of ZCT is to detect the unbalance current from life and neutral or life with

ground. The tripping of an ELCB is depending on the sensitivity of the ZCT. For

resident, usually ELCB that is being used is a 0.1 A that means if there is any unbalance

current ≥100mA, the ZCT will induced current and then de-energizes the magnetic coil

in black box, so that the mechanical switch can be disconnected [12].

Figure 2.6 shows the operation of the ZCT. Operation of ZCT is same like the

Clamp Meter that is used to detect current in a line. In case 1, when the current flow

through life and neutral line is same, there is no unbalance current detect in the ZCT thus

there is no induced current produced by the ZCT. In case 2, when there is unbalance

current between life and neutral, ZCT will produced an induced current and then it will

send to the signal to the magnetic coil resulting in tripping of the ELCB [12].

14

Because Iin = Iout, there is no induced current produced by the ZCT

Because Iin = Iout, thus there is induced current produced by the ZCT.

The higher difference in input and output current, result in more induced

current produced.

Figure 2.6: Operation of ZCT

2.7 Basic Concept of ELCB

The basic concept of the ELCB is if there are fault occurred, ZCT will sense the fault

and send the signal to the ELCB to cut the power to the load (tripped). After 10 second

the ELCB will connect back the power to the load, after that if the ELCB is remain

connected with the load that means the fault is temporary like lightning. Meanwhile if

after the ELCB is connected back to the load and it still detect any fault, it will switch on

back. The cycle will be repeated for 3 times, if the fault is still detected, the ELCB will

isolated the power from the load and it will display the fault is permanents like short-

15

circuit or over-current. Until the fault is correct by the user, the ELCB will remain

tripped and the user need to manually switch on the ELCB after the fault is correct to

avoid electrical hazard [13].

2.8 Operation of ELCB

Based on the Figure 2.7 when the faulty occurred, ZCT will detect the imbalance value

of current L and N, so the induced current will happened in ZCT, induced current that

reached the min value to activate the coil will be send as a signal to the Black Box, when

the coil is activated, it will sense the contact to trigger and automatically the mechanical

switch is triggered and this will cut off the supply from main line [14].

Figure 2.7: Earth Leakage Circuit Breaker Operation Flow

16

2.9 Conclusion for previous report

REFERENCES METHOD DESCRIPTION RESULT

Development of

Earth Leakage

Circuit Breaker to

operate automatic

Reclosed Using PIC

Microcontroller.

(Syahrum Nizam bin

Md Arshad 2008)

Using the

GSM modem.

Least-Bandwidth lag

Least-causes electronic interference

Using the main ELCB and backup ELCB

Least-no backup supply

By using the

gsm modem, the user can get the alert for the situation of the circuit breaker at home

During the main ELCB tripped, the LCD will display the main is tripped and backup is on

Perhaps the

greatest disadvantage of GSM is that multiple users share the same bandwidth. With enough users, the transmission can encounter interference

Another disadvantage of GSM is that is can interfere with certain electronics, such as pace makers and hearing aids. Such interference is due to the fact that GSM uses a pulse-transmission technology. As a result, many locations such as hospitals and airplanes require cell phones to be turned off

In this case without the backup supply will be a problem to user while in permanent fault condition

17

REFERENCES METHOD DESCRIPTION RESULT “DEVELOPMENT

OF EARTH

LEAKAGE

CIRCUIT

BREAKER WITH

AN AUTO RE-

CLOSER UNIT ’’

(Mohd Tarmizi Bin

Rahim May,2009)

Using the

Pspice sofware

Least-PSpice is a much more complex circuit simulator

Least-PSpice does not allow data visualization during simulation

Using the main ELCB and backup ELCB

Least-no backup supply

PSpice is

a spice analog circuit and digital logic simulation program for Microsoft windows

During the main ELCB tripped, the LCD will display the main is tripped and backup is on

PSpice allows the

user to select specific components with industry standard part number and specifications. Searching for these components can take up more of the user’s time when constructing the circuit.

In this case

without the backup supply will be a problem to user while in permanent fault condition

CHAPTER 3

METHODOLOGY

3.1 Introduction

In order to complete this project, development of the method and step is an important to

make sure this project was successful without any problems. This chapter is based on the

following major parts discussed in the following section. It deals with the actual design

and construction of the project. Methodology is the process to find the suitable project,

make the researching and study all of the project information, choose the suitable

method for design this project, planning the time and selecting the equipment such as

material is needed and computer software program.

This project is divided into two main parts: hardware and software development

which require to be done for 2 semester of learning. The main purpose of using

flowchart method as Figure 3.1 is to ensure the project is successfully succeeded to

achieve the aim and objective. Moreover, it is used to define and analyze by easy-to-

understand diagrams showing the step-by-step picture of process.

19

3.2 Planning

Figure 3.1: Flowchart of Planning

20

3.2.1 Phase 1: Preliminary Investigation

This phase is about formulating the problem, determining the objective and defines the

project scope. This phase focus on investigating and establishing the idea to perform the

design selected. Usually in this stage, it is important to collect all the data related to the

idea from any source for information. Basically several problems that maybe obtain in

this project will be listed in this phase to due overcome any constraint in this project

development.

3.2.2 Phase 2: Analysis and Specification

In this phase, literature review will be perform based on material collected from

previous publish project material. Furthermore, hardware and software specification and

requirement also will be determined. Hardware that will be used is microcontroller

circuit. Software chosen for this project is MPLAB and PROTEUS. The suitable

methods for the hardware development and program interfacing are observed.

3.2.3 Phase 3: Design

This phase will focus on designing circuit and developing program for the system. Flow

Chart methodology will be applied in this project. As companion, flowchart, schematic

and circuit diagram will be design during this phase.

3.2.4 Phase 4: Development and Integration

After development of a circuit and program, next phase is integrating and combine both

parts. In this phase troubleshoot and modifications are needed if any errors occur during

the testing phase. Any errors occur will be improved by modifying the program or

troubleshooting the circuit.

21

3.2.5 Phase 5: Testing

Testing phase are divided into two level first level is unit step, where the system will be

tested part by part. Second level is integration test where the complete combine system

between hardware and software part will be examined. The analysis and finding are

important to ensure success and effectiveness of the project.

3.2.6 Phase 6: Maintenance

The final phase is mainly about looking for the improvement in current system.

Basically, the recommendation is suggested to overcome the failure on project

requirement.

3.3 Hardware Development (Research Requirement)

3.3.1 ELCB Hardware Design

From the Figure 3.2 the basic build of an ELCB only consist 4 basic components, which

are ZCT, “Black box”, Mechanical switch and Test Resistor. Functions of ZCT are to

detect unbalance current in life and neutral wire that is installed through ZCT. If there

are any unbalance current detected in ZCT, ZCT will induced current and then the

induced current will be sent to “black box”. “Black box” basic build is a magnetic coil

that is round by copper wire. When the Induced current from ZCT entered “Black Box”,

magnetic coil in the “black box” is de-energized and then it will trigger the tripping

mechanical switch.

22

Figure 3.2: Component and Structure of ELCB

3.3.2 ELCB with an Automatic Unit Hardware Design

From the Figure 3.3, the hardware is the improved design from basic ELCB in Figure

3.2 above. The Relay Driver replaced the function of mechanical switch in old ELCB.

Function of ELCB disconnects a circuit whenever it detects that the electric current is

not balanced between the energized conductor and the return neutral conductor.

Transformer 240/12Vac is used and then it will be converting from 240 volt ac from

power line to 12 volt and 5 volt dc by using half wave rectifier circuit. The 12 volt dc is

used to energize Power Relay and Alarm. The 5 volt dc is used to energize PIC

microcontroller and LCD (Liquid Crystal Display).

23

Figure 3.3: Component and Structure of ELCB with an Automatic unit

For IC Voltage Regulator, the model of LM7812 was used to step down the

voltage from 240V to 12V for Power Relay and Alarm. The model of LM7805 was used

to step down the voltage from 12V of Transformer to 5V for PIC microcontroller and

LCD (Liquid Crystal Display).

For the Microcontroller circuit, PIC that is used is PIC16F877A. Relay Driver is

selected as switching because the reliability as Electronic switch that can be operated at

high voltage and current.

3.3.3 UPS Configuration

There are several configurations that being used by manufacturers in the design of UPS

systems. Each configuration has its own benefit and drawbacks. The common UPS that

sells at the market has 3 types. The three main types are stated as below:

24

3.3.3.1 Standby or off-line system

In normal operation, main power or utilities power is supplied directly to the load. Until

there are either a power failure, sag or spike occurs, the UPS then switches on

instantaneously the load onto battery-powered inverter, providing the back-up power. It

disconnects the main or utility power until it returns to an acceptable level. In this

design, the UPS unit only charges the battery when it is running on utility power. Most

off-line UPS system employ a square wave inverter output, or modified square wave

output.

Figure 3.4: Off-Line System Diagram

3.3.3.2 Double conversion on-line system

The double conversion on-line system provides complete isolation of the load from

mains service. It operate by, converting incoming utility AC power to DC and then

convert the DC back to AC to power the connected equipment. The batteries are directly

connected to the DC level, which provides an excellent filter for removing line noise.

Thus providing high quality conditioned power to the loads. This system yields many

benefits. Firstly, it allows the UPS to use almost any incoming power, including

generators. Second, this design allows the UPS to easily change incoming voltages and

even frequencies. Third, because the load is always powered by the inverter, when

74

REFERENCES

[1] http://en.wikipedia.org/wiki/Earth_leakage_circuit_breaker

[2] “13 A RCD ACCESSORIES”. TLC (Southern) Ltd.

http://www.tlc.direct.co.uk/Technical/Accessories/RcdSockets/RcdSockets.htm.R

etrieved on 2007-07-12

[3] “Elektron”, ELECTRICAL SHOCK AND FIRE HAZARD PROTECTION

CONQUERING THE LIMITATIONS. September 1993.

[4] Alvarion. Lightning Protection. (1-21) October 2005

[5] Mitja Koprivsek, Development Trend of Residual Current Circuit Breakers, IEC

1008-1-Residual current operated circuit breakers, grad. Eng. Of el. Eng. ETI

d.d Izlake. 2004

[6] SABS 767 – Earth Leakage Protection Units, 1982.

[7] Indo asian fusegear ltd. Stopshock Residual Current Circuit Breaker. (1-8) 2000

[8] Suruhanjaya Tenaga. Prohibition on The Use Of Voltage Operand Earth

Leakage Circuit Breaker (ELCB). Tuesday, 13 March 2007.

[9] Robert L. Boylestad, Louis Nashelsky, ELECTRONIC DEVICE AND CIRCUIT

THEORY ninth edition, pearson education international (639-643) (778-782).

[10] Mohd Azraie bin Suarin “Automatic Tester Devive for Earth Leakage Circuit”.

Universiti Malaysia Pahang: Bachelor thesis (2008).

75

[11] Syahrum Nizam bin Md Arshad “Development of Earth Leakage Circuit Breaker

to operate automatic Reclosed Using PIC Microcontroller”.Universiti Teknologi

Malaysia: Bachelor thesis (2008).

[12] Wan Rusmaezame bin Wan Mahmood “Development of Earth Leakage Circuit

Breaker Using solenoid” .Universiti Teknologi Malaysia: Bachelor thesis (2008).

[13] Abdullah Asuhaimi bin Mohd Zin, Md Shah Majid, Saifunizam Abd Khalid,

Alias Mohd Yusof, Power System Engineering, 2011.

[14] Earth Leakage Circuit Breaker, catalog, www.peopleelectric.cn/AB

[15] Raja Mohd Taufika Raja Ismail, Peranti Pengesan Voltan Pemutus Litar

Bocor Ke Bumi, Thesis, 2002.

[16] Geoff Trudgen (July 2009),IC Crystal Oscillator Circuit, www.rakon.com

(UK Ltd).

[17] A. Lindgren, \New method for high current measurements," electrical

engineering,Royal Institute of Technology,. Thesis work made for Danaher

Motion (Kollmorgen Stockholm AB) September 2003.