The Final Report of Project Monthly Electric Bill Saving System

CHAPTER 1

INTRODUCTION

1.1

Project Background

Now days, people do not know how much electrical energy use in a month because there is no system to alert them. So, with this Monthly Electric Bill Saving System (MEBSS) project, it will help people to know how much they use and also they can set the amount (RM) they want in electricity bill at the end of the month. It has an LCD that display everything such as energy usage in kWh unit and the bill need to pay in RM unit.  This system already converts from energy usage kWh to a billing in Ringgit Malaysia (RM) by referring a tariff domestic from TNB. They also can set the amount (RM) in this MEBS system. The buzzer will give sound in that house if the amount is reached. If it reach  early of the month they can add another amount (RM) in MEBS System. With this system they can budget for electrical bill and save money.

For example:

 If Mr. A wants to pay only RM20 at the end of the month, so Mr. A need to set RM20 in MEBSS. But if the MEBSS trip before the end of the month, then Mr A need to add the amount at the MEBSS. Let say, Mr. A add another RM10, so, the calculation for that month is RM20 (early seating) + RM10 (after setting) = RM30. So Mr. A will know that he needs to pay RM30 for electrical bill.

This project is fully controlled by embedding system a program that program in microcontroller PIC16f877a. An embedded system is a special-purpose system in which the computer is completely programmed with or dedicated to the device or system it controls. Unlike a general-purpose computer, such as a personal computer, an embedded system performs one or a few predefined tasks, usually with very specific requirements. Since the system is dedicated to specific tasks, design engineers can optimize it, reducing the size and cost of the product. Embedded systems are often mass-produced, benefiting from economies of scale.

	1.2	Project Statment

In every house the energy meter only shows the watt usage per hour. That is why the consumer always did not know how much electrical energy use in a month because there is no system to alert them. Beside that the consumer did not know how to read the energy meter. So, the consumer did not know how much they need to pay for the electric bill by the end of the month. Other than that, because of the consumer did not how to read the energy meter, it is so hard for them to budget their electrical bill.

 So, with this Monthly Electric Bill Saving System (MEBSS) project, it will help people to know how much they use and also they can set the amount (RM) they want in electricity bill at the end of the month. It has LCD that display everything such as energy usage in kWh unit and the bill need to pay in RM unit.  This system already converts from energy usage kWh to a billing in Ringgit Malaysia (RM) by referring a tariff domestic from TNB. They also can set the amount (RM) in this MEBS system. The buzzer will give sound in that house if the amount is reached. If it reach early of the month they can add another amount (RM) in MEBS System. With this system they can budget for electrical bill and save money.

1.3    Objective

To acknowledge the consumer regarding their electric bill they need to pay by the end of the month. To make the consumer more easier to know the usage of energy in digit number from the LCD display. The consumer can budget for electric bill by setting the amount to system and after reaching the amount the system will give alert to consumer.

CHAPTER 2

LITERATURE REVIEW

2.1

Project Background

After doing a research, there have many informative and project that has connected to the proposed project. In a present day there already change from the analog energy meter to a digital energy meter in a certain place and the other places still have used the analog energy meter. Now, according to Md. Mejbaul Haque project that I have research. He creates a single phase digital prepaid energy meter based on two microcontrollers and a single phase energy meter IC. His digital prepaid energy meter does not have any rotating parts. The energy consumption is calculated using the output pulses of the energy meter chip and the internal counter of microcontroller (ATmega32). According to research, his microcontroller (ATtiny13) is used as a smart card and the numbers of units recharged by the consumers are written in it. A relay system has been used which either isolate or establishes the connection between the electrical load and energy meter through the supply mains depending upon the units present in the smart card. Energy consumption (kWh), maximum demand (kW), total unit recharged (kWh) and the rest of the units (kWh) are stored in the ATmega32 to ensure the accurate measurement even in the event of an electrical power outage that can be easily read from a 20×4 LCD. As soon as the supply is restored, energy meter restarts with the stored values. A single phase prepaid energy meter prototype has been implemented to provide measurement up to 40A load current and 230V line to neutral voltage.Necessary program for microcontrollers are written in c-language and compiled by Win-AVR libc compiler.

            For my opinion, using a card reader is hard for us to reload the prepaid card if the card is empty. Need to make sure the card has credit, if we want use an electrical. For my project, the most important contributions of other related projects/findings for my project is to make sure the consumer know how much they use the energy, besides this project is already convert from energy usage (kWh) to Ringgit Malaysia (RM),so the consumer will know how much for electric bill in a month that need to pay. Other than that, this project have saving system, so they set the amount if they want to budget in an electric bill by set how much they want to pay into the system.

	2.2	Development of Achitecture

The system architecture of microcontroller based single phase digital prepaid energy meter for improved metering system is shown in figure 1.

Fig. 1 Prepaid energy metering system

The energy metering system consists of Energy Meter chip, Microcontroller, Voltage and Current controlling unit, Smart cart, Relay and Liquid Crystal Display (LCD).

·          Energy Meter IC generally produces electrical pulses proportional to the power consumed by the consumer and the power supply of microcontroller.

·          Microcontroller calculates the energy consumed by the consumer utilizing the output of Energy Meter Chip and programs loaded on the microcontroller.

·          Voltage and Current controlling unit feeds the actual current and voltage of load connected to consumer side to the energy meter chip.

·          Smart Card interfaces with the microcontroller unit in which the number of units recharged by the consumer are written.

·          Relay mainly performs the opening and closing of a connection between energy meter and load through supply mains depending upon the number of units present in the smart card at a moment.

·          Liquid Crystal Display shows the energy consumption, number of unit recharged by the consumer, rest of the unit and maximum demand.

The energy billing system is shown in figure 2. The energy billing system mainly consists of a user operated PC, USB Burner circuit and Smart card.

2.3    Summary of literature review

This paper has demonstrated for measuring the electrical energy consumption of an electrical load for two wire distribution systems with the proposed energy meter as an alternative to the conventional electromechanical meters. This microcontroller based energy meter prototype has been implemented to provide measurement up to 40 A load current from a 230 V line to neutral voltage. The proposed energy meter is capable of measuring energy consumption for all loads conditions i.e. power factor and non-sinusoidal voltage and current waveforms. It does not posses any rotating parts that help in the prevention of meter tampering, which is an attractive feature for the utilities. The proposed energy meter includes a “no load threshold” feature that will eliminate any creeping effects in the meter. In addition, the process of reading the energy consumption is facilitated by the LCD display that is simpler than that for the analog meters which reduces human errors while noting down the meter reading. This energy meter has the potential to change the future of the energy billing system in Bangladesh. The energy billing system may help the energy distribution companies to reduce costs and increase profits, to improve metering and billing accuracy and efficiency, and to contribute the energy in a sustainable way. To recharge the microcontroller chip, it must be taken to the server terminal or unit. The energy billing system provides employment for nearly 2-3 people in every server terminal for jobs like recharging the smart card and processing the distribution of power in a convenient way. In future, mode of recharging the smart card can be improved by wireless communication between the server terminal and energy meter unit.

CHAPTER 3

METHADOLOGY

3.1

Electronic

3.1.1        Power Supply

3.1.1.1 Transformer to step down voltage from 240V to 12V.

A transformer consists of two coils (often called 'windings') linked by an iron core, as shown in the figure below. There is no electrical connection between the coils, instead they are linked by a magnetic field created in the core.

Step-down transformers

Step down transformers is to reduce a voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains voltage to a safer low voltage.   The input coil is called the primary and the output coil is called the secondary. 

For this project, it will use a step down transformers that give output 9V or 12V as picture below.

The ratio of the number of turns on each coil, called the turn’s ratio, determines the ratio of the voltages. A step-down transformer has a large number of turns on its primary (input) coil which is connected to the high voltage mains supply, and a small number of turns on its secondary (output) coil to give a low output voltage.

Below are transformers formula,

Turns ratio = Vp/ V_S = Np/N_S

Power Out= Power In

V_S X I_S=V_P X I_P

Vp = primary (input) voltage

Np = number of turns on primary coil

Ip  = primary (input) current     

Transformers have two great advantages over other methods of changing voltage:

1.      They provide total electrical isolation between the input and output, so they can be safely used to reduce the high voltage of the mains supply.

2.      Almost no power is wasted in a transformer. They have a high efficiency (power out / power in) of 95% or more.

3.1.1.2 Bridge rectifier to convert from AC to DC voltage.

A Bridge Rectifier ( Full wave Rectifier )

The circuit in figure 3 addresses the second of these problems since at no time is the output voltage 0V.  This time four diodes are arranged so that both the positive and negative parts of the AC waveform are converted to DC.  The resulting waveform is shown in figure 4.

When the AC input is positive, diodes A and B are forward-biased, while diodes C and D are reverse-biased.  When the AC input is negative, the opposite is true - diodes C and D are forward-biased, while diodes A and B are reverse-biased.

One disadvantage of the full-wave rectifier is that there is a voltage loss of 1.4V across the diodes.  Why not 2.8V as there are four diodes, that is because there is only two of the diodes are passing current at any one time.

While the full-wave rectifier is an improvement on the half-wave rectifier, its output is still not suitable as a power supply for most circuits since the output voltage still varies between 0V and Vs-1.4V.  So, if you put 12V AC in, you will 10.6V DC out.

The formula Bridge full wave Rectifier is,

	Full wave   Bridge
Number of   diodes	4
PIV of diodes	Vm
D.C output voltage	2Vm/phi
Vdc,at no-load	0.636Vm
Ripple factor	0.482
Ripple         frequency	2f
Rectification    efficiency	0.812
Transformer    Utilization    Factor(TUF)	0.812
RMS voltage Vrms	Vm/√2

            A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally. So, in this project it will use 4 x 1N4001 diode (as picture below).

Diode type 1N4001

3.1.1.3 Filter

This is why the 'smoothing' block is required. Its because the output come from bridge rectifier is not suitable for power supply. So to give the output more smooth we use filtering circuit by using only one capacitor as shown in figure 1 below.

The output waveform in figure 2 shows how smoothing works.  During the first half of the voltage peaks from the rectifier, when the voltage increases, the capacitor charges up.  Then, while the voltage decreases to zero in the second half of the peak, the capacitor releases its stored energy to keep the output voltage as constant as possible.  Such a capacitor is called a 'smoothing' or 'reservoir' capacitor when it is used in this application.

If the voltage peaks from the rectifier were not continually charging up the capacitor, it would eventually discharge and the output voltage would decrease all the way down to 0V.  The discharging that does occur between peaks gives rise to a small 'ripple' voltage.  The amount of ripple is affected by a combination of three factors:

• The value of the capacitor.  The larger the capacitor value, the more charge it can store, and the slower it will discharge.  Therefore, smoothing capacitors are normally electrolytic capacitors with values over 470μF.
• The amount of current used by the circuit.  If the circuit connected to the power supply takes a lot of current, the capacitor will discharge more quickly and there will be a higher ripple voltage.
• The frequency of the peaks.  The more frequent the voltage peaks from the rectifier, the more often the capacitor will be charged, and the lower the ripple voltage will be.

To calculate the ripple voltage, it will use this formula below.

 V_r = the ripple voltage in Volts

 I = the current taken by the circuit in Amps

 C = the value of the smoothing capacitor in Farads

 F =the frequency of the peaks from the full-wave rectifier, in Hertz.

The ripple voltage should not be more than 10% of Vs - if it is, increase the value of the smoothing capacitor.

So in this project, the value capacitor for filter circuit is 470uF ( as the picture below ).

Capacitor 470uF

3.1.1.4 IC Regulated (LM7805) to regulate the voltage 5V to supply to Microcontroller.

There are many types of regulator IC and each type will have different pin-outs and will need to be connected up slightly differently.  Therefore, this article will only look at one of the common ranges of the regulator, the 78xx series.

There are seven regulators in the 78xx series, and each can pass up to 1A to any connected circuit.  There are also regulators with similar type numbers that can pass a higher or lower current, as shown in the table below.  In addition, variable regulators are available, as are regulators that can provide negative regulation voltages for circuits that require them.

Type Number		Regulation Voltage		Maximum Current		Minimum Input Voltage
78L05		+5V		0.1A		+7V
78L12		+12V		0.1A		+14.5V
78L15		+15V		0.1A		+17.5V
78M05		+5V		0.5A		+7V
78M12		+12V		0.5A		+14.5V
78M15		+15V		0.5A		+17.5V
7805		+5V		1A		+7V
7806		+6V		1A		+8V
7808		+8V		1A		+10.5V
7812		+12V		1A		+14.5V
7815		+15V		1A		+17.5V
7824		+24V		1A		+26V
78S05		+5V		2A		+8V
78S09		+9V		2A		+12V
78S12		+12V		2A		+15V
78S15		+15V		2A		+18V

If using a regulator after the smoothing block of the power supply, then not need to worry about the ripple voltage, since the whole point of using a regulator is to get a stable, accurate, known voltage for your circuits. However, if the ripple voltage is too large and the input voltage to the regulator falls below the regulated voltage of the regulator, then of course the regulator will not be able to produce the correct regulated voltage.  In fact, the input voltage to a regulator should usually be at least 2V above the regulated voltage.  In our power supply circuit, the input to the 7805 regulator is around 12V, and the regulation voltage is 5V, so there is plenty of headroom.  The maximum input voltage to any 78xx regulator is 30V.

Filtering is performed by a large value electrolytic capacitor connected across the DC supply to act as a reservoir, supplying current to the output when the varying DC voltage from the rectifier is falling. The capacitor charges quickly near the peak of the varying DC, and then discharges as it supplies current to the output. Filtering significantly increases the average DC voltage to almost the peak value (1.4 × RMS values).

To calculate the value of the capacitor (C),

                                    C = ¼*√3*f*r*Rl

              Where,

                              f = supply frequency,

                              r = ripple factor,

                             Rl = load resistance

The 78xx, 78Mxx, and 78Sxx regulators all have the pin-out shown in the left of figure 1. The 78Lxx series, shown in the right of figure 1. The connection circuit of regulator 78xx, as shown in figure 2. For this project, it use 7805 because give regulated output is 5V and the micro controller only need 5V of source.

IC regulator LM7805

3.1.2 Micro-chipAD7755( energy ic)

This application describes a low-cost, high-accuracy watt-hour meter based on the AD7755. The meter described is intended for use in single phase, two wire distribution systems. However the design can easily be adapted to suit specific regional requirements, for example in the Malaysia power is usually distributed to residential customers as single-phase, three-wire. The AD7755 is a low-cost, single-chip solution for electrical energy measurement. The AD7755 is comprised of two ADCs, reference circuit, and all the signal processing necessary for the calculation of real (active) power. The AD7755 also includes the direct drive capability for electromechanical counters (i.e., the energy register), and has a high-frequency pulse output . The AD7755 provides direct drive capability for this type of counter. The AD7755 also provides a high-frequency output which give the output for 100 pulse per 1kWh.

The test circuit from datasheet AD7755

The picture of AD7755

Design Calculations

Design parameters:

Line voltage = 220 V (nominal)

IMAX = 40 A (Ib = 5 A)

Counter = 100 imp/kWh

Meter constant = 3200 imp/kWh

Shunt size = 350 μΩ

100 imp/hour = 100/3600 sec = 0.027777 Hz

Meter will be calibrated at Ib (5A)

Power dissipation at Ib = 220 V × 5 A = 1.1 kW

Frequency on F1 (and F2) at Ib = 1.1 × 0.027777 Hz

= 0.0305555 Hz

Voltage across shunt (V1) at Ib = 5 A × 350 μΩ = 1.75 mV.

To select the F1–4 frequency for Equation 1 see the AD7755 data sheet, Selecting a Frequency for an Energy Meter Application section. From Tables V and VI in the AD7755 data sheet it can be seen that the best choice of frequency for a meter with IMAX = 40 A is 3.4 Hz (F2). This frequency selection is made by the logic inputs S0 and S1—see Table II in the AD7755 data sheet. The CF frequency selection (meter constant) is selected by using the logic input SCF. The two available options are 64 F1(6400 imp/kWh) or 32 × F1(3200 imp/kWh). For this design, 3200 imp/kWh is selected by setting SCF logic low. With a meter constant of 3200 imp/kWh and a maximum current of 40 A, the maximum frequency from CF is 7.82 Hz. Many calibration benches used to verify meter accuracy still use optical techniques. This limits the maximum frequency that can be reliably read to about 10 Hz. The only remaining unknown from equation 1 is V2 or the signal level on Channel 2 (the voltage channel).

 From Equation 1 on the previous

Therefore, in order to calibrate the meter the line voltage needs to be attenuated down to 248.9 mV.

The data sheet AD7755 is in APPENDIX

3.1.3 Microcontroller PIC16f877a (brain system)

3.1.3.1 Introduction

          This section is the control unit of the whole project. It basically consists of a Micro controller with its associated circuitry like Crystal with capacitors, Reset circuitry, Pull up resistors (if needed) and so on. The Micro controller forms the heart of the project because it controls the devices being interfaced and communicates with the devices according to the program being written.  

   

A Micro controller consists of a powerful CPU tightly coupled with memory RAM, ROM or EPROM), various I / O features such as Serial ports, Parallel Ports, Timer/Counters, Interrupt Controller, Data Acquisition interfaces-Analog to Digital Converter (ADC), Digital to Analog Converter (ADC), everything integrated onto a single Silicon Chip.

          Micro controller has  memory such as RAM, ROM or EPROM and peripherals on a single chip so development of a similar system with a micro controller reduces PCB size and cost of the design.

3.1.3.2 Micro controller use in the project PIC16f877A

 This devices are available in 40-pin packages is shown as picture below.

PIC16f877a

            This microcontroller Pic16f877a is a main component in the system. It will be programmed in C language to do the whole operation in the system. All the description on the Pic16f877a can be see on data sheet appendix ( ) . Each pin of the pic16f877a  will do a different operation. For PORT A it use to count the pulse coming from energy ic AD7755. For PORT B it is use to send data interrupt function and keypad number to LCD. For PORT C use as push button. For PORT D is use as LCD.

Device features.

Port Function.

3.1.4 Liquid Clear Display (LCD)

LCD will display everything such as energy usage in kWh unit and the bill need to pay in RM unit. 

In 8 bit mode all the Data lines DB0 to DB7 are being used for transferring the data to the LCD but in 4-bit mode only 4 line form DB4 to DB7 are being used to transfer the  8 bit wide data in two peaces one after another . We cannot display any data on the LCD until all the required internal command registers of the LCD are not being properly initialized.

To display a charter on LCD we need to give  commands in ASCI code. It is because the LCD will read in ASCI code only. Below are shown an ASCI code for LCD.

3.1.5 Keypad 3x4

Description of Basic Operation

The Keypads are low-voltage, microprocessor-based user interfaces designed to operate with a host controller. The devices consist of twelve (12) touch-sensitive buttons that operate via patented TouchCell™ Field-Effect  touch technology. The buttons are arranged in a standard 3x4 numeric keypad layout.

The Keypads are provided with the following features:

• Backlit touch-sensitive keypads

• Audio beeper feedback

This keypad will help the consumer to key in their amount in the system, so that the system will know how much amount consumer want for their electric bill.

3.1.5.1 MM74C922

Keypad 3x4 will interface with mm74c922 as to give the output to the lcd. Below are the connection for the interface.

From the  block diagram above we know that the keypad will give output which is A,B,C and D  if key pressed. The output will based on the truth table. From the output truth table it will combine with the ASCI code from LCD and display numeric number in the LCD.

3.1.6 Relay

A relay is use to trigger the system to send the signal in automatic operation which can be control by microcontroller system.

A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and most have double throw (changeover) switch contacts as shown in the diagram.

Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits, the link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 5V/12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil.

Relays are usuallly SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. For further information about switch contacts and the terms used to describe them please see the page on switches. Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.

The relay's switch connections are usually labelled COM, NC and NO:

COM = Common, always connect to this, it is the moving part of the switch.

NC = Normally Closed, COM is connected to this when the relay coil is off.

NO = Normally Open, COM is connected to this when the relay coil is on.

3.1.6.1 ULN2003

This relay is interface by ULN2003 which give the signal from microcontroller to the relay. Below picture are shown the operation of ULN2003.

 

When the signal from microcontroller is low the relay will switch on the bulb. When the signal is high the relay will switch off the bulb.

The ULN2003 is a monolithic high voltage and high current transistor arrays. It consists of seven NPN pairs that feature high-voltage outputs with common-cathode clamp diode for switching inductive loads. The collector-current rating of a single pair is 500mA. The pairs may be paralleled for higher current capability. Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED gas discharge),line drivers, and logic buffers. The ULN2003 has a 2.7kW series base resistor for each pair for operation directly with TTL or 5V CMOS devices.

This are the diagram for ULN2003 in datasheet.

3.1.7 Buzzer

A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or piezoelectric. Typical uses of buzzers and beepers include alarm devices, timers and confirmation of user input such as a mouse click or keystroke.

In this project the buzzer will act and make a sound to alert the consumer that their amount is reach.

	3.2	Electrical

3.2.1 Single phase Meter

Single phase induction type energy meter is also popularly known as watt-hour meter. Single phase energy meter is a device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device. It typically calibrated in billing units, the most common one being the kilowatt hour (kWh). Periodic readings of electric meters establish billing cycles and energy used during a cycle. Single phase energy meter are consists of following components:

1. Driving system

2. Moving system

3. Braking system and

4. Registering system

Connection Diagram of Single phase energy meter

3.2.1.1 Driving system

It consists of two electromagnets, called “shunt” magnet and “series” magnet, of laminated construction. A coil having large number of turns of fine wire is wound on the middle limb of the shunt magnet.

This coil is known as “pressure or voltage” coil and is connected across the supply mains. This voltage coil has many turns and is arranged to be as highly inductive as possible. In other words, the voltage coil produces a high ratio of inductance to resistance.        

An adjustable copper shading ring are provided on the central limb of the shunt magnet to make the phase angle displacement between magnetic field set up by shunt magnet and supply voltage is approximately 90 degree.

The copper shading bands are also called the power factor compensator or compensating loop. The series electromagnet is energized by a coil, known as “current” coil which is connected in series with the load so that it carry the load current. The flux produced by this magnet is proportional to, and in phase with the load current.

3.2.1.2 Moving system

The moving system essentially consists of a light rotating aluminum disk mounted on a vertical spindle or shaft. The shaft that supports the aluminum disk is connected by a gear arrangement to the clock mechanism on the front of the meter to provide information that consumed energy by the load.

The time varying (sinusoidal) fluxes produced by shunt and series magnet induce eddy currents in the aluminum disc. The interaction between these two magnetic fields and eddy currents set up a driving torque in the disc.

The number of rotations of the disk is therefore proportional to the energy consumed by the load in a certain time interval and is commonly measured in kilowatt-hours (Kwh).

3.2.1.3 Braking system

Damping of the disk is provided by a small permanent magnet, located diametrically opposite to the a.c magnets. The disk passes between the magnet gaps. The movement of rotating disc through the magnetic field crossing the air gap sets up eddy currents in the disc that reacts with the magnetic field and exerts a braking torque.

By changing the position of the brake magnet or diverting some of the flux there form, the speed of the rotating disc can be controlled.

3.2.1.4 Registering or Counting system

The registering or counting system essentially consists of gear train, driven either by worm or pinion gear on the disc shaft, which turns pointers that indicate on dials the number of times the disc has turned. The energy meter thus determines and adds together or integrates all the instantaneous power values so that total energy used over a period is thus known.

3.2.2 Distribution Board

A distribution board (or panel board) is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit, in a common enclosure. Normally, the protective are include is the main switch, and in recent boards, one or more Residual-current devices (RCD) or Residual Current Breakers with Overcurrent protection (RCBO), will also be incorporated. There are also have the Miniature Circuit Breaker as the switch circuit.

3.2.2.1 Electrical protective device

Equipment applied to electric power systems to detect abnormal and intolerable conditions and to initiate appropriate corrective actions. These devices include lightning arresters, surge protectors, fuses, and relays with associated circuit breakers, recloses, and so forth.

The disturbances in the normal operation of a power system occur. These may be caused by natural phenomena, such as lightning, wind, or snow; by falling objects such as trees; by animal contacts or chewing; by accidental means traceable to reckless drivers, inadvertent acts by plant maintenance personnel, or other acts of humans; or by conditions produced in the system itself, such as switching surges, load swings, or equipment failures. Protective devices must therefore be installed on power systems to ensure continuity of electrical service, to limit injury to people, and to limit damage to equipment when problem situations develop. Protective devices are applied commensurately with the degree of protection desired or felt necessary for the particular system.

The protective use in this project is

1.                  Main Switch

2.                  Residual Current Circuit Breaker (RCCB)

3.                  Miniature Circuit Breaker ( MCB )

3.2.2.1.1 Switch Fuse 32A

The switch fuse is used as the main switch in low voltage switchgears in the industry for distributing power and protecting motors, cables and other devices against short circuits and overloads.

3.2.2.1.2 RCCB

A residual-current circuit breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Ground Fault Condition is defined as: An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment or earth. Such an imbalance may indicate 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. RCCBs are designed to disconnect quickly enough to prevent injury caused by such shocks. They are not intended to provide protection against overcurrent (overload) or short-circuit conditions.

RCCB is operate by measuring the current balance between two conductors using a differential current transformer. This measures the difference between the current flowing through the live conductor and that returning through the neutral conductor. If these do not sum to zero, there is a leakage of current to somewhere else (to earth/ground, or to another circuit), and the device will open its contacts.

Residual current detection is complementary to over-current detection. Residual current detection cannot provide protection for overload or short-circuit currents, except for the special case of a short circuit from live to ground (not live to neutral).

The incoming supply and the neutral conductors are connected to the terminals at (1) and the outgoing load conductors are connected to the terminals at (2). The earth conductor (not shown) is connected through from supply to load uninterrupted.

When the reset button (3) is pressed the contacts ((4) and hidden behind (5)) close, allowing current to pass. The solenoid (5) keeps the contacts closed when the reset button is released. The sense coil (6) is a differential current transformer which surrounds (but is not electrically connected to) the live and neutral conductors. In normal operation, all the current down the live conductor returns up the neutral conductor. The currents in the two conductors are therefore equal and opposite and cancel each other out.

Any fault to earth (for example caused by a person touching a live component in the attached appliance) causes some of the current to take a different return path which means there is an imbalance (difference) in the current in the two conductors (single phase case), or, more generally, a nonzero sum of currents from among various conductors (for example, three phase conductors and one neutral conductor).

This difference causes a current in the sense coil (6) which is picked up by the sense circuitry (7). The sense circuitry then removes power from the solenoid (5) and the contacts (4) are forced apart by a spring, cutting off the electricity supply to the appliance.

The device is designed so that the current is interrupted in milliseconds, greatly reducing the chances of a dangerous electric shock being received.

The test button (8) allows the correct operation of the device to be verified by passing a small current through the orange test wire (9). This simulates a fault by creating an imbalance in the sense coil. If the RCD does not trip when this button is pressed then the device must be replaced.

3.2.2.1.3 MCB

       Circuit breakers are electrical switching devices for protecting and controlling the electricity supply to respective electrical circuits. Circuit breakers protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. Electrical systems in residential, commercial and industrial applications usually include a panelboard for receiving electrical power from a utility source. The electrical power is then delivered from the panelboard to designated branch circuits supplying one or more loads.

        Overload protection is provided by a thermal element which, when heated by the increased current, will cause the circuit breaker to trip and interrupt the power. Use of circuit breakers is widespread in modern-day residential, commercial and industrial electric systems, and they constitute an indispensable component of such systems toward providing protection against over-current conditions. Various circuit breaker mechanisms have evolved and have been perfected over time on the basis of application-specific factors such as current capacity, response time, and the type of reset (manual or remote) function desired of the breaker.

           Typically, various types of circuit interrupters are connected to the branch circuits to reduce the risk of injury, damage or fires. Circuit interrupters include, for example, circuit breakers, contactors, motor starters, motor controllers, other load controllers and receptacles having a trip mechanism. In the event an overcurrent condition occurs, electrical contacts within the circuit breaker will open, stopping the flow of electrical current through the circuit breaker to the equipment. Circuit breakers have an operating mechanism and trip means, such as a thermal trip assembly and/or magnetic trip assembly, which are automatically releasable to effect tripping operations and manually resettable following tripping operations.

The components inside the circuit breaker:

1.     Actuator lever - used to manually trip and reset the circuit breaker. Also indicates the status of the circuit breaker (On or Off/tripped). Most breakers are designed so they can still trip even if the lever is held or locked in the "on" position. This is sometimes referred to as "free trip" or "positive trip" operation.

2.     Actuator mechanism - forces the contacts together or apart.

3.     Contacts - Allow current when touching and break the current when moved apart.

4.     Terminals

5.     Bimetallic strip.

6.     Calibration screw - allows the manufacturer to precisely adjust the trip current of the device after assembly.

7.     Solenoid

8.     Arc divider/extinguisher

3.2.2.1.4 Load

Load affects the performance of circuits that output voltages or currents, such as sensors, voltage sources, and amplifiers. Mains power outlets provide an easy example: they supply power at constant voltage, with electrical appliances connected to the power circuit collectively making up the load. When a high-power appliance switches on, it dramatically reduces the load impedance.

In this project I using switch socket outlet as socket for load. Below is the connection of the load.

           

3.3

Software

3.3.1 MPLAB IDE v8

The current version of MPLAB IDE is version 8.63. It is a 32-bit application on Microsoft Windows and includes several free software components for application development, hardware emulationand debugging. MPLAB IDE also serves as a single, unified graphical user interface for additional Microchip and third-party software and hardware development tools.

Both Assembly and C programming languages can be used with MPLAB IDE v8. Others may be supported through the use of third-party programs.

This software is to simulate the C language programming for the Pic16f877a microcontroller chip.

3.3.2 HI-TECH C

HI-TECH C compiler for PIC16 MCU implements the optimizations of Omniscient Code Generation™ (OCG). Whole program compilation technology to provide denser code and better performance for development on PIC16 MCU. HI-TECH C compiler is use in MPLAB to create a C programming to the PIC16 series microcontroller unit.

3.3.3PROTEUS

 

Proteus PCB design combines the ISIS schematic capture and ARES PCB layout programs to provide a powerful, integrated and easy to use suite of tools for professional PCB Design..

All Proteus PCB design products include an integrated shape based auto router and a basic SPICE simulation capability as standard. More advanced routing modes are included in Proteus PCB Design Level 2 and higher whilst simulation capabilities can be enhanced by purchasing the Advanced Simulation option and/or micro-controller simulation capabilities.

Proteus PCB design is used to create a circuit of the microcontroller or project and interfacing with hi tech c compiler in MPLAB for the c code

CHAPTER 4

MONTHLY ELECTRIC BILL SAVING SYSTEM

4.1  Block Diagram

            As we can see the block diagram above, the single phase energy meter supply will go to the load, energy ic (AD7755) and distribution board. So, for the distribution board it will have all protective devices to protect the circuit from the fault current. After that it will go to the power supply where in this operation the power supply will convert from 230VAC to 5VDC to make the PIC16f877a and AD7755 to turn ON. AD7755 will sense the energy usage from the load and send the signal in pulse signal which 100pulses is equal to 1kWh. The signal will send to a microcontroller. A micro controller will read the signal, calculating and display to the LCD. The LCD will display the energy usage and the amount of the electric bill in Ringgit Malaysia (RM).

            The keypad function is to make the consumer can preset the amount they want to use for a particular month.

If the set amount is equal to the amount use the microcontroller will send the signal to the relay. So, the relay will turn on the buzzer.

4.2  Flow Chart

4.3  The Body of MEBSS

From the Diagram  above  we can see live (red), neutral (black) , and earth (green) connects the single phase energy meter. The analog energy meter is to show the actual reading of the energy usage. The output of energy meter will go to the distribution board were in this distribution board have a protective device such as Main Switch, Residual Current Circuit Breaker, and Miniature Circuit Breaker (MCB). The protective device is to protect the circuit from having short circuit, overload current, earth fault and etc that can damage the circuit. There have three outputs will go out from distribution board. For the first output will go to the Step down transformer where in this situation. The transformers will step down the voltage from 240V AC to 12V AC. The step down transformer is needed because the circuit cannot handle 240VAC voltage for the power supply circuit. When a step down voltage is 12V AC it still cannot be a power supply for the circuit because it is still in AC voltage while the power supply circuit need is DC voltage. So there has rectifier, to convert AC to DC voltage. The second output is going to the load where this port is for the load such as lamp, and other electrical component. And the third output will go to the circuit where in this circuit it will read and give the reading and display to the LCD. The LCD will display, energy usage (kWh) and the electric bill (RM).

4.4  Programming Code of MEBSS

4.4.1 Main Body Program

//--Main Funtion --

void main(void)

{

            TRISA=0xFF; // Set PORT A as an INPUT

            TRISB=0x0F; // Set PORT B as an IN/OUTPUT

            TRISC=0x0F; // Set PORT C as an IN/OUTPUT

            TRISD=0x00; // Set PORT D as Output

                                                                                                                             

            T0CS = 1;                    // Select external Clock source

            T0SE = 1;                    // Increment on falling edge

            PSA = 1;                     // Timer0 without prescaler

            TMR0 = -1;   // Reset Timer0 Counter

            TMR0IE = 1; /* Enable timer0 interrupts */

            TMR0 = -1;                 //0x00; /* Timer0 Counter */

            GIE=1; // Global interrupt enable

            TMR0IF=0; //Clear TMR1 interrupt flag

            PEIE=1; //Peripheral Interrupt Enable

            //--Clear memory of amount set

            write_eeprom(50,0);

            write_eeprom(51,0);

            write_eeprom(52,0);

            amountenter();

            wait_for_one_press( ); // press RC3 to active the system

           

            lcd_init();

            lcd_putc ("Welcome! MEBSS ");      

            lcd_gotoxy(2,0);

            lcd_putc ("is ACTIVATE");

            clearmemory();

            while (1)

            {         

                        currentkwh();

                                                                                                                       

            }

}

4.5  Problem

4.5.1        Earth Fault

When the running the hardware system with the circuit. I have a problem which is the earth fault connection. This is an earth fault problem when I turn on the system only the Residual Current Circuit Breaker (RCCB) is tripped. This RCCB is functional or operating when only the earth fault is happening. Below picture shows normal Phase and Neutral wire connections to the meter. Note that current going through the Phase wire is the same as coming out of the neutral wire (IP = IN).

An earth fault means some of the load has been connected to another ground potential and not the neutral wire. The picture below shows a Partial Earth Fault Condition where one of the loads is connected to the ground and thus part of the return current I2 does not go through the meter. Thus the current in the neutral wire IN, is less than that in the Phase or live wire (IP).

So to detect this condition, I am using the test pen to check the connection. Then the problem have encountered, where there have connection from neutral and earth circuit has been wrong. So the connection change and check with the circuit diagram. Than no more earth fault happen.

4.5.2 Transformers is Heating          

Ihaveg a problem with the step down transformers where itbecomeseheatedt and haveburnedn smells when the hardware system isturnedn on. After checking the connection, actually the connection of transformers is wrong as shown as picture 1. Then I change the connection as shown picture 2, the transformer heat is normal and do not have the burn smell.

4.5.3        Neutral have power ( Line power)

When the hardware system is turned on, on the neutral connection have power. The neutral connection it supposes carry no power which is 0V. But when I check the connection to the hardware system is good, thus on the circuit that having problems. It's because, the Live (power) connection  is touching with the neutral connection. That's why the neutral connection is having a power. To eliminate the power of neutral, I must make sure the live (power) connection not touching the neutral connection. It will have a big problem when the neutral has a power.  The circuit hardware will not stable.

CHAPTER 5

RESULTS

5.1 CIRCUIT DIAGRAM

5.1.1 Power Supply

5.1.2 Energy IC (AD7755)

5.1.3 PIC16f877a ( microcontroller )

5.2 RESULT SIMULATION

            From the result above it show when the amount that consumer want is enter by pressing the keypad.

         
  After amount is enter the microcontroller will detect and count the pulse at pin RA4. After the count is equal to 100 pulse. The LCD will display the “current kWh” is 1 kWh.

So,

100 pulse = 1kWh

? pulse = 10kWh

? pulse = 10kWh x 100pulse

             = 1, 000 pulse.

            When the pulse detect, the system will calculate the kilo-watt hour ( kWh ). After that, the kWh will convert to electrcic bill. The calculationis refer by tariff TNB in APPENDIX ( ).

            Because of the amount set is equal to the amount use which is RM2. So, the microcontroller will send signal to relay to turn on a buzzer.

CHAPTER 6

CONCLUSION

6.1 SUMMARY

Electric bill is not easy to control or manage because we cannot see how much we use the energy. With this project Monthly Electric Bill System is useful for all consumer because this project help consumer to estimate their electrical energy usage bill at end of the month. It can control or manage by preset the amount that need by end of the month to the microcontroller. This project will give advantage knowledge because it combines the in two operations which are software and hardware. The software are using computer to program into the microcontroller. This will make we know about the programming instead of electrical knowledge only. By having the electrical knowledge and combine with programming knowledge it will make advantage for the future job. This project can be used in home because all consumers are using electric to operate. They can save more electric bill instead to waste it.

APPENDIX