INTRODUCTION

Load protector is a device used in conjunction with the power supply for protection of electrical equipment operating on single or three phase power supply.  Mankind is a witnessing an era of technological development, technology is changing our life in a way which is hard to imagine in the past; modern age technology is teaching us the way to develop highly sophisticated instruments. The invention of the solid-state devices had lead to revolution in the field of power electronics. This revolution has made human beings to use the semiconductor devices for control and switching purposes.  To protect the electrical equipments from transients in power supply is of the major concern in power system. Power surges, power spikes, voltage overloads, low voltage conditions, and line degradation are some of the problems associated with power supplies. Therefore some arrangements should be done to protect the apparatus from these inevitable conditions.Load protector is most commonly used device to fulfill this purpose. Earlier individual circuits were required for individual fault detection. As a result workspace required was large for multiple fault detection on a power system at a single time. Earlier system has a disadvantage that the links were in deactivated state at normal condition and get activated on any fault detection. Therefore any intruder signal can disrupt the process of activation. Today all instrumentation system pertaining to industrial process control as well as domestic applications, like elevator control and centralized air conditioning control, involve some type of automatic fault finding facility.

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This facility detects the faulty condition of the system and draws the attention of the operator towards it, enabling him to take suitable remedial action so as to ensure the proper operation.

One such method is annunciation in which activation of a visual or a mechanical indicator takes place when a remote switch or device has been activated due to occurrence of fault in certain part of the system. An audio alarm may also be accommodated for fault detection & control processing.

Here we had provided a microcontroller based load protector along remote switching facility that detects two different faulty conditions (under voltage/over voltage) and informs the operator about them so that corrective action should be taken for respective fault. Here it is assumed that each faulty condition results in closing of one of the two interlock links. We had used two flashing light emitting diodes (LEDs) corresponding to each of the two links, to detect the under voltage/ over voltage condition. Here two additional LEDs are used to indicate normal condition status and remote switching status respectively. With advancement in technology more efficient and lossless load protector are available now-a-days.

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Chapter 1

COMPONENT DETAILS

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1.1 POWER SUPPLY

Our project Microprocessor Based wireless Load Protector requires 12 volt and 5 volt D.C. supply for overall operation of circuitry. In this system a step down transformer is used to convert 230 V AC into 12-0-12 volt AC supply. Input voltage 230 V AC and 12 Volt AC at secondary winding. Now this 12 V AC supply first rectified by two PN diode (IN4007) the ripple removed with the help of filter capacitor (1000 mfd/25V) and we get 12 V DC supply. Since this DC voltage is unregulated i.e. when voltage variation in input or variation in load then this DC supply change according the variation in input voltage or load. For smooth and proper functioning of any DC circuitry it is necessary to feed constant DC supply so this unregulated supply first regulated by IC 7812. Unregulated DC supply fed to input (pin 1 of IC) of regulator IC (7812, 12 Volt regulator IC) and pin 2 is ground or common and regulated 12 V DC output taken from pin 3 of regulator IC.

Now this 12 V DC regulated supply fed to the input (pin 1) of 5 Volt regulators IC (7805), pin no. 2 is common for input-output and output taken from pin no.3 of regulator IC. Two capacitor 100mfd/25 V and 1000 mfd/25 V connected between 12V and 5V output terminal respectively for stabilization.

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1.2 INTEGRATED CIRCUITS

A chip made up of a number of components contained in a single package. One semiconductor chip can contain two or more transistors, several resistors and capacitors and many individual diodes or other components. A single integrated circuit may be used to replace many discrete components. In addition to the space saving features of ICs owing to fact that they possess almost identical processing, which enables them to be closely matched in characteristics? The closer such circuit elements are matched, the greater the reliability of the circuit. An integrated circuit is one in which circuit components such as transistors, diodes, resistors, capacitors etc. is automatically the part of a small semiconductor chip. An integrated circuit comprises of a number of circuit components (e.g. transistor, diodes, resistor etc.) and their interconnections in a single small package to perform a complete electronic function. In an IC the various components are automatically a part of a small semiconductor chip and the individual components cannot be removed or replaced.

1.3 DIODE

PN Junction diodes: - It is constituted of a P type region and an N type region formed in the same crystal structure. Some of the conduction electrons near the junction diffuse into the P type semiconductor from the N type semiconductor across the junction combining with the holes. The loss of electron makes the N type semiconductor positively charged and hence the neutralization of the holes. On the other hand makes the P-type semiconductor negatively charged. This region where positive and negative charges develop is called depletion region.

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If a P region is made positive with respect to the N region by an external circuit, then junction is forward biased and junction has a very low resistance to the flow of current. Holes in the positive P type materials are attracted across the junction to the negative side and the free electron in the N type material are like wise attracted to the opposite side. If a N region is made positive with respect to the P region by an external circuit, the PN junction is said to be reverse biased the positive holes and the free electrons are repelled from the junction. The region adjacent to each side of the junction free of charge carriers is called depletion regions. A voltage below the break down voltage of the junction, the current flow may be only a small leakage current, which is called the reverse saturation current. An ideal diode is one which behaves as a perfect conductor when forward biased and as a perfect insulator when reverse biased. Obviously in such a hypothetical situation forward resistance equal to zero and potential barrier voltage is considered negligible.

1.4 RESISTOR

Resistors are the electronic components used to control the current passing through the circuit. They are calibrated in ohms. In other word resistance are circuit elements having the function of introducing electrical resistance into the circuit. There are three basic types:(a) Fixed resistor (b) Rheostat(c) Potentiometer A fixed resistor is a two terminal resistor whose electrical resistance is constant. A rheostat is a resistor that can be changed in resistance value without opening the circuit to make adjustment. A potentiometer is an adjustable resistor with three terminals, one at each end of the resistor element and third movable along its length.

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1.4.1 FIXED RESISTOR

There are three basic types of fixed resistors. 1. Carbon composite resistor.2. Wire wound resistors.3. Film resistors.In the circuit we use carbon composition resistors.

1.4.2 CARBON COMPOSITION RESISTORS

Molded fixed composition resistors are limited for general purpose use in electronic equipment. These are able to withstand configuration, have very low inductance and capacitance, can tolerate rough handling installation and are inexpensive.

CHARACTERISTIC OF COMPOSITION TYPE RESISTOR

1. Inexpensive and small in size.2. Reliability is good.3. Stability is good4. Voltage coefficient is appreciable 0.02.5. High frequency characteristics are satisfactory.6. Noise is appreciable.7. Temperature coefficient is large.

1.5 CAPACITOR A capacitor essentially consists of two conducting surface separating by a layer of an insulating medium called dielectric. The conducting surface may be in the form of either circular or rectangular plates or be of spherical or cylindrical shape. The purpose of a capacitor is to store the electrical energy by electrostatic stress in the dielectric.

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The property of a capacitor to store electricity may be called its capacitance. Its capacitance is dependent on three factors (a) the surface area of the plates of which it is composed (b) the thickness of the insulating material (c) the material of which the dielectric is composed of. Essentially a system in which two or more metal plates (conductor) are placed in close proximity to each other & are separated by an insulating material called the dielectric. When the plates of the capacitor are connected to a voltage Source there will be a surplus of electrons on the plate connected to the negative side and a shortage of electron on a plate connected to the positive side of the voltage source.

The surplus of electrons on the negative plate will repel the electrons on the other plate driving them back toward the positive plate will attract electrons from the negative plate of the voltage source. The electron flow will continue until the negative and positive charges on the capacitor plates are equal to the voltage source. When this condition exists the capacitor is said to be charged. When the voltage source is disconnected the condition of unbalance that has been setup on the capacitor plates will remain thus providing a means of storing electricity in the capacitor ,whose capacitance is equal to ratio between the magnitude of the charge on the plates and the voltage difference between the plate.

1.5.1 CERAMIC CAPACITOR A capacitor is so named because of ceramic dielectrics. One type of the ceramic capacitor uses a hollow ceramic cylinder as dielectric material, the plates consists of thin films of metal deposited on the ceramic cylinder. A second type of ceramic capacitor is manufactured in the shape of a disc. After leads are attached to each side of the capacitor the capacitor is completely cored with an insulating moisture proof coating. Ceramic capacitor usually ranges in value between 1pf to 0.01 µf and may be used with voltage as high as 30,000 volts.

1.5.2 ELECTROLYTIC CAPACITOR

A capacitor that uses an aluminum foil as an anode and a current carrying fluid or electrolytic as a cathode. A coating of aluminum oxide

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forms the dielectric while another aluminum foil is used as an electrical contact with the electrolyte since the electrolyte is often a liquid it is contained in a porous paper that is wound between layers of foil to prevent leaking. By using many sheets of foils as a common contact several capacitors can be built into single contact container. The aluminum oxide and the foil form a special type of semiconductor that enables current to pass through the oxide film towards the foil. This can be accomplished in one direction only thus an electrolytic capacitor is a polarized device. It cannot be used with alternating current and sees most of its applications as part of the filtering circuit in a D.C. power supply. A less common type of electrolytic capacitor is non-polarized and can be used in AC circuits. This type has the oxide film on both aluminum foils with an electrolytic. Fluid forming a floating negative plate.

They are available in many different capacitance and voltage values as well as case designs and configurations. Values ranges from a fraction of microfarads to several thousand and in voltage rating from 3V D.C to approximately 600 V D.C.

1.6 TRANSFORMER

A transformer is a static piece of apparatus by means of which electric power in one circuit is transformed into electric power of the same frequency in another circuit. It can raise or lower the voltage in a circuit but with a corresponding decrease or increase in current. The physical basis of a transformer is mutual induction between two circuits linked by a common magnetic flux.

1.6.1 TRANSFORMER CONSTRUCTION

A transformer consists of two coils having mutual inductance and a laminated steel core. The two coils are insulated from each other and the steel core, other necessary parts are some suitable container for the assembled core and winding; a suitable medium for insulating the core and its windings from its container; suitable bushing for insulating and bringing out the terminal of winding from the tank. In all type of transformer the core is constructed of transformer sheet steel laminations assembled to provide a continuous magnetic path with a minimum of air gap included, the steel used is of high silicon content, sometimes heat treated to produce a high permeability and low hysteresis loss. The eddy current loss is minimized by laminating the core.

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According to construction there are two types of transformer known as i) Core type

ii) Shell type

1.6.1.1 CORE TYPE TRANSFORMER

The coils used are form wound and are of the cylindrical type. The general form of these coils may be circular or over all rectangular. In small size core type transformers, a simple rectangular core is used with cylindrical coils which are so wound as to fit over a cruciform core sections.

1.6.1.2 SHELL TYPE TRANSFORMER

In shell type transformer the coils are form wound but are multi-layer disc type usually wound in the form of pancakes. The different layers of such multilayer discs are insulated from each other by paper. The complete winding consists of tackled discs with insulation spaces between the coils.

1.7 TRANSISTOR

A transistor consists of two p-n junctions formed by sandwiching either p-type or n-type semiconductor between a pair of opposite types. Accordingly; there are two types of transistors, namely:-

(1) n-p-n-transistor (2) p-n-p transistor

An n-p-n transistor is composed of two n-type semiconductor separated by a thin section of p-type. However a p-n-p transistor is formed by two p-sections separated by a thin section of n-type.In each type of transistor, the following points may be noted:-

(1)There are two p-n junctions. Therefore, transistor may be regarded as a combination of two diodes connected back to back.

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(2) There are three terminals, taken from each type of semiconductor

(3) The middle section is very thin layer. This is the most important factor in the function of a transistor.

1.8 RELAY

A relay is a device that functions as an electrically operated switch. Most relays are electro magnetically operated. Current through a coil generates a magnetic field that attracts an armature, which in turn closes or opens the electrical contacts. Operation is in millisecond range. Relay is manufactured in great variety. Classification by application is very difficult;

Because each variety of relay is used in many widely dissimilar applications. The following class of relays is arranged in order of increasing specializations; 1. General purpose relay.2. Power relay.3. Telephone relay.4. Card actuated relay.5. Sensitive relay.6. Crystal relay.7. Dry reed relay.8. Mercury wetted reed relay.9. P.C. board relay.10. Coaxial relay.11. Stepping relay.12. Instrument relay.13. Hybrial relay and solid state relay.The relay used in above said circuit is described here -

1.8.1 GENERAL PURPOSE RELAY:-

The general purpose electro magnetic relay along with its different parts. The part of the relay are an iron is and its surrounding coil of wire, an

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iron yoke which provides a low reluctance path for magnetic flux, the yoke being shaped so that the magnetic circuit can be closed by a movable piece of iron called that armature and set of contacts. The armature is hinged to the yoke and held by a spring in such a way that there is an air gap in the magnetic circuit. When an electric current flows through the coil the armature is connected to the iron core & electrical switching contacts are mounted on the armature when relay coil which is energized. These movable contacts break their connection with one set of fixed contact (normally closed) and close a connection to previously open contact. When electric power is removed from the relay coil a spring return the armature to its original position. To prevent the armature from reaming struck to the end of core because ruminant magnetism (the residual magnetism that remains in the core when no current flow in the coil). A separator made of non-magnetic material maintains a small residual air gap between the armature face and coils or wound on separate bobbins made of plastic bakelite with suitable enameled copper wire. Then it is pottered with rubber compound Or impregnated varnish to protect from moisture. The end wire terminals are soldered to the terminals and no joints is used during the coil winding since it breaks due to expansion of wire material.

Phosphorus bronzes are widely used for contact strips to give spring tension so as to reduce bouncing and contacts are riveted to it of different contact materials. General purpose relay can be classed by size, miniature, small and standard.

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CHAPTER 2

CIRCUIT MANUFACTURING

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2.1 SOLDERING Soldering is the process of joining two metallic conductors. The joint where the two metal conductors are to be joined or fused is heated with a device called soldering iron and then an alloy of tin and lead called solder, is applied which melts and covers the joint. The solder cools and solidifies quickly to ensure a durable connection between the joined metals. Covering the joint with solder also prevents oxidation of the metal surface.

2.1.1 HOW TO SOLDER Efficient soldering is very important for assembling for any electronic circuit. A poor soldered joint or connection in electronic circuits is the cause of most of the power system problems. Given below are some important steps to be followed in good and efficient soldering practice.

1. Use of correct type of soldering iron and solder. Avoid the use of excessive flux.2. Keep the soldering iron hot during the working period and let rest on its stand when not in use.3. All component’s leads and wires should be thoroughly cleaned to remove dust before soldering. 4. Enough heat is applied to the joints so that the solder metal flows freely over the joint.5. Over heating of components in P.C.B. is avoided. Overheating may results in damage of components of P.C.B.6. Too much solder is not used to avoid short circuits between conduction paths on a P.C.B.

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2.2 PCB DESIGN Layout of desired circuit diagram and its preparation is first and most important operation in any printed circuit board manufacturing process. First of all layout of component side is to be made in accordance with available component dimensions. The following points are to be observed while forming the layout of P.C.B.Between two components, sufficient space should be maintained. High wattage/ max. dissipation components should be mounted at a sufficient distance from semiconductors and electrolytic capacitors.The most important point is that the components layout should be in proper compromise with copper side circuit layout. The two most popular boards are single sided boards and the double sided boards. The single sided P.C.B. is widely used for general purpose application where the cost is to be low and the layout is simple.

2.2.1 PREPARING CIRCUIT LAYOUT First of all actual size circuit layout is to be drawn on the copper side of the copper clad board. Then enamel paint is applied on the tracks of connection with the help of a sharp brush .We have to apply the paints surrounding the point at which the connection is to be made. It avoids the disconnection of painting work, it is allowed to dry.

2.2.2 DRILLING After completion of painting work, holes of 1/32 inch (1mm) diameter are drilled at desired points where we have to fix the components.

2.2.3. ETCHING The removal of copper on the plate apart from the printed circuit is known as etching. For this process the copper clad board with printed circuit is placed in the solution of FeCl3 (Ferric chloride) with 3-4 drop of HCl in it and are kept so for about 2 hrs. And is taken out when all excess copper is removed from the P.C.B.

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After etching, the P.C.B. is kept in clean water for about half an hour in order to get P.C.B. away from dry acidic components which may cause poor performance of the circuit. After the P.C.B. has been thoroughly washed, paint is removed by soft piece of cloth dipped in thinner or turpentine. Then P.C.B. is checked as per the layout. Now the P.C.B. is ready for use.

CHAPTER 3

CIRCUIT DISCRIPTION

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Circuit comprises of four sections:-

1. POWER SUPPLY

2. AT89C51 MICROCONTROLLER.

3. RELAY CONTROL CIRCUIT 4. I.R. SENSOR CIRCUIT

1. POWER SUPPLY:-

The Regulated Power Supply is required for the proper functioning of all the components in an electronic system. The microcontroller requires regulated output of 5V for its operation, while 12V is required for operating relays and motors. The Regulated Power Supply circuit basically requires an AC supply of 220-230V, step-down transformer, rectifier circuit, regulator and stabilizing capacitors.

1.1 CIRCUIT DESCRIPTION

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Fig 2.1 Regulated Power Supply

The present section shows the operation of power supply circuits built using filters, rectifiers, and then voltage regulators. Starting with an ac voltage, a steady dc voltage is obtained by rectifying the ac voltage, then filtering to a dc level, and finally, regulating it to obtain a desired fixed dc voltage. The regulation is usually obtained from an IC voltage regulator. Parts of a typical power supply and the voltage at various points in the unit is shown in fig 2.1. The ac voltage, typically 120 V r.m.s, is connected to a transformer, which steps that ac voltage down to the level for the desired dc output. A diode rectifier then provides a full-wave rectified voltage that is initially filtered by a simple capacitor filter to produce a dc voltage. This resulting dc voltage usually has some ripple or ac voltage variation. A regulator circuit can use this dc input to provide a dc voltage that not only has reduced ripple voltage but also remains at the same dc value even if the input dc voltage varies somewhat or the load connected to the output dc voltage changes. This voltage regulation is usually obtained using one of a number of popular voltage regulator IC units.

There are two voltage regulator ICs used. One is LM7812, for 12V regulated output and the other is LM7805, for 5V regulated output. An indicator circuit may be introduced to check operation using a resistor and an LED.

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1.2 IC VOLTAGE REGULATORS:

Voltage regulators comprise a class of widely used ICs. Regulator IC units contain the circuitry for reference source, comparator amplifier, control device, and overload protection all in a single IC. Although the internal construction of the IC is somewhat different from that described for discrete voltage regulator circuits, the external operation is much the same. IC units provide regulation of either a fixed positive voltage, a fixed negative voltage, or an adjustably set voltage.

A power supply can be built using a transformer connected to the ac supply line to step the ac voltage to desired amplitude, then rectifying that ac voltage, filtering with a capacitor and RC filter, if desired, and finally regulating the dc voltage using an IC regulator. The regulators can be selected for operation with load currents from hundreds of milli amperes to tens of amperes, corresponding to power ratings from milli watts to tens of watts.

1.2.1 THREE-TERMINAL VOLTAGE REGULATORS:

Fig 2.2 shows the basic connection of a three-terminal voltage regulator IC to a load. The fixed voltage regulator has an unregulated dc input voltage Vi, applied to one input terminal, a regulated output dc voltage, Vo, from a second terminal, with the third terminal connected to ground. For a selected regulator, IC device specifications list a voltage range over which the input voltage can vary to maintain a regulated output voltage over a range of load current. The specifications also list the amount of output voltage change resulting from a change in load current (load regulation) or in input voltage (line regulation)

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Transformer Rectifier Filter IC Regulator Load

Fig 2.2 Basic Connection of IC Regulator to a Load.

1.2.2 FIXED POSITIVE VOLTAGE REGULATOR

The Series 78 regulators provide fixed regulated voltages from 5 to 24 V. Fig 2.2 shows how one such IC, a 7812, is connected to provide voltage regulation with output from this unit of +12V dc. An unregulated input voltage Vi is filtered by capacitor C1 and connected to the IC’s IN terminal. The IC’s OUT terminal provides a regulated + 12V which is filtered by capacitor C2 (mostly for any high-frequency noise). The third IC terminal is connected to ground (GND). While the input voltage may vary over some permissible voltage range, and the output load may vary over some acceptable range, the output voltage remains constant within specified voltage variation limits. These limitations are spelled out in the manufacturer’s specification sheets.

IN OUT7805GNDFrom

Transformersecondry

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Fig 2.3 Fixed Voltage Regulators.

2. AT89C51 MICROCONTROLLER

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4Kbytes of Flash Programmable and Erasable Read Only Memory (PEROM).The device is manufactured using Atmen’s high density nonvolatile memory technology and is compatible with the industry standard MCS-51Ô instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with flash on a monolithic chip, the Atmen AT89C51 is a powerful microcomputer which provides a highly flexible and cost effective solution to diversified control applications.

The AT89C51 provides the following standard features: 4Kbytes of Flash, 28 bytes of RAM, 32 I/O lines, two 16-bit timer/counters, five vector two-level interrupt architecture, a full duplex serial port, and on-chip oscillator and clock circuitry. In addition, the AT89C51 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the next hardware reset.

General-purpose microprocessors contain no RAM, no ROM and no I/O ports on the chip. For this reason they are commonly referred to as the general-purpose microprocessors. System designers using general-purpose microprocessors must add RAM, ROM and I/O ports and timers externally to make them functional. They are bulkier and expensive.

The microcontrollers on the other hand have a CPU in addition to a fixed amount of RAM, ROM and I/O ports and timers all embedded together on one chip. The on chip ROM & Ram and ports make microcontrollers ideal for many applications in which cost and space are critical.

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2.1 MICROCONTROLLER INTERFACING

The fig 2.5 shows the circuit diagram of the Microcontroller Interfacing circuit for built around AT89C51 microcontroller. Since the AT89C51 (IC1) doesn’t have a program memory, an EPROM is used to store the information of the system.

AT89C51 has 4K internal EPROM, so we can directly program the code into AT89C51 and interface other circuitry /devices to it.

The combination of resistor and capacitor provides the necessary slow-rising power-on-reset signal to the microcontroller’s reset input pin 9. For the working of any microcontroller it is necessary to have a clock pulse. We can provide the clock pulse either by external source or generate it within microcontroller. In this model, we generate clock pulse internally with the help of crystal oscillator and capacitor. One 12 MHz crystal is connected between pin 18 & pin 19 of microcontroller, and two capacitors (22 pf each) are connected through pin 17 & pin 18 to ground.

In this circuit port P1 and port P2 are used as input & output ports respectively and port 3 is used as a control port (output). Initially logic levels of Port 1, Port 2 & Port 3 of microcontroller are high i.e. +5 volt at each pin, we can change the logic to low (0 volt) with the help of software.

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Fig 2.4 AT89C51 Block Diagram

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Now four inputs from device / sensor circuitry are connected to the Pins P1.0, P1.1, P 1.2 and P1.3 and four outputs for relay operation are connected to the Pins P2.0, P2.1, P2.2 and P2.3.

Fig 2.5 Microcontroller Interfacing Circuit.

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Now, when the supply switch is turned ON, the circuit, as per the software starts continual scanning of the status of Pins 1.0 to P1.3 and sends respective status at Pins P2.0 to Port 2.3, if at any time any vehicle enters the system, then sensor circuit sends a signal to the microcontroller, and the microcontroller in turn sends respective high or low signal to follow the proper sequence for switch activation.

3. Relay Controller Circuit:

Controller circuit is basically made from transistor-relay driving circuit, in which a collector of NPN transistor is connected to the negative supply and collector is connected to the positive supply via PN junction diode (IN4007). One relay is connected parallel to the diode and base of transistor connected to the output of microcontroller or o/p of sensor circuit through current limiting resistors. When no biasing at transistor then transistor is cutoff region so relay is de-energized therefore output equipment of in "OFF" condition. Now when output of microcontroller of sensor circuit is high then transistor is saturation condition so current flow from collector to emitter via relay coil so relay is energized hence output equipment is now turn "ON".

Fig 2.6 Relay Control Circuit.

In this system if voltage level is above from the predefined level then it signals fault condition.

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In this system an NPN Transistor are used for voltage level monitoring system. A 12V relay connects to the collector of transistor and emitter is ground. Two terminal taken from transistor one from base (through current resistance). When input voltage to be monitored is feed to the base of transistor then smoothly voltage increases. When voltage level is below from defined level (the voltage level can be set with the help of variable resistance) there is no sufficient biasing at base of transistor so transistor goes to cutoff region and relay is turn off. Now when applied voltage is greater than or equal to biasing voltage then transistor is saturate and relay is turn on, which further activates the microcontroller input port p1.4 which shows fault condition or over voltage condition.

4. I.R. SENSOR CIRCUIT

The IR remote control circuit can be used for any simple on-off function. The advantage is that this circuit is absolutely free from ambient light interference and provides control range of about 10 feet without use of any focusing lens.  Block diagram of the circuit is shown in circuit diagram. Transmitter section consists of a power supply, an oscillator, and an output stage, where as the receiver section comprises power supply, an infrared detector module, time delay circuit with noise filter, bi-stable flip-flop, and an output section.

4.1. TRANSMITTER CIRCUIT

In the transmitter section ICI (555) is wired as an astable multivibrator with a centre frequency of about 36 kHz. When switch S1 is pressed, the circuit gets energized. Output of ICI is a square wave. The two infrared LEDs connected at its output transmit IR beams modulated at the same frequency (36 kHz). The oscillator frequency can be shifted slightly by adjusting preset VR1.

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Fig 4.1 Infrared Transmitter

4.2. RECEIVER CIRCUIT

The receiver uses an infrared sensor module which is commonly used in various electronics field for sensing the IR signals from the transmitter section. The sensor module incorporates a detector diode, an SMD (surface mounted device) IC which consists of a band-pass filter, an amplifier and a demodulator on a small PCB placed inside a small tin cube enclosure to get rid of unwanted electro-magnetic interference. When switch S1 is in "ON" condition the transmitter is "ON”, and IR LEDs generate IR beams with a modulating frequency of 36 kHz. In this circuit IR LEDs are directly driven by the 555 timer output, and no series current limiting resistor is used with them. This is because at the high operating frequency, the internal resistance of the battery and the impedance offered by the wires and components leads are high enough to keep the average LED current within its specifications. The IR signal from the transmitter is sensed by the sensor and its output pin of sensor goes low and after some time output pin again high. Due to this, first transistor turn off then turn 'on'. i.e. When IR signal is received by sensor, output of the sensor is high and transistor goes high and thus relay is in "ON" condition.

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fig.4.1 Receiver circuit

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CHAPTER 4

PRINCIPLE & WORKING

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This scheme provides a two way facility for the operation:-

1. Automatic switching.

2. Manual switching by Remote. The whole circuitry can be divided in two parts. First part is a receiver circuit that offers a facility of remote switching. Here we are using an infrared receiver. The next part of the circuitry is Relay drive circuit which is automatically controlled through microcontroller. In this circuit a NPN transistor works as a switch. At initial state the transistor is in cut off region in normal condition. Whenever the voltage across the base of the transistor exceed from 2V (knee point) the transistor is driven into saturation region and it enables the relay to trip. A potential divider can be provided across the base and emitter of the transistor which provides facility to select the desired value of the minimum and maximum tripping value of the relay.

Automatic switching

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This mode of operation has a great advantage that whenever abnormal operating condition is generated in the power supply it protects the load connected in the power system. The load protector circuitry operates differently under high/low voltage conditions as explained below:-

Under high voltage condition:-

Whenever high voltage condition is generated in the power system, as per the previous setting done in the relay drive circuitry through variable resistor, as soon as the relay reaches its pickup value it provides the trip signal & cuts off the load from the circuit & hence load gets disconnected through the supply & remains protected from over voltage. The voltage at which relay is to be tripped can be set by varying the variable resistor setting. Under low voltage condition:- Similarly whenever low voltage condition is generated in the system, as per the previous setting done in the relay drive circuitry through variable resistor , as soon as the relay reaches it provides the trip signal & cuts off the load from the circuit & hence load gets disconnected through the supply & remains protected from under voltage. For low & high voltage pickup value setting to different variable resistors are provided.

Manual switching

It enables the remote switching of load for this purpose infrared receiver is used. Manual switching circuit is constituted of two parts:-

1) Transmitter circuit: - Transmitter circuit having an astable multivibrator generates a clock pulse when push to on switch is pressed. This clock pulse fed to the L.E.D. which generates infrared signal.

2) Receiver circuit: - It is basically a toggle circuit .Whenever it receives signal through the infrared sensor it changes its states. The output of the receiver is fed to the microcontroller by an electromagnetic relay and also to the main relay drive circuit.

As the receiver receives the signal, the biasing transistor at receiver circuit which is thrown to saturation region from cutoff

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region, enables the decade counter .The decade counter starts counting the pulse. As the pulse goes from high to low it enables the microcontroller port 1(input port).On arrival of each negative pulse port 3(output port) of microcontroller gets enabled and causes to apply +5volt at the input of relay drive circuit which ultimately causes the biasing transistor to thrown into saturation region, that forces the main relay to trip. Along with this microcontroller also serves the facility of visual indication of various operating modes of the system (i.e. normal, over voltage, under voltage and remote switching) by employing LED.

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CHAPTER 5

MERITS AND DEMERITS

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MERITS:-

Load protector is an essential part of various instruments. Since it provides protection of electrical appliances against over and under voltage so thus reduces the electrical hazard and increases the life of the apparatus.Some of the merits are giving below:-

1. Since its switching speed is high it protects devices from voltage spike (voltage- transient) comes in the power supply mains.

2. It offers both automatic as well as manual switching through remote.

3. Its compact size offer suitability to works with any home appliances

4. It reduces external wiring between actual machines and control room.

5. Reduce large number of electronics components and various

circuitries for various parameters.

6. Future modification can be easily done. Suppose we install

new machine & adopt monitoring for that system then we can

monitor / control this equipment. By minor changes in main circuit.

7. This system can be easily interface with any PLC system.

DEMERITS:-

1.Since various parameter conditions transmitted through transmitter at different frequencies so its alignment should be perfect otherwise malfunctioning

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CHAPTER 6

APPLICATION

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Since this is the basic protection device for apparatuses that’s why it is widely used in present scenario. Some of the application of this scheme is given below.

1. High wattage domestic appliances like refrigerator, television, washing machine etc.

2. In Industries it is mostly used where automatically load restoration is required.

3. In any industry like power plant, rolling mill we can monitor & control temp., voltage, frequency, pressure and controls them.

4. This system can be used as time based controlled system with slightly modification in software.

5. This circuit also used in automation system.

6. This circuit also used as a wireless security purpose with minor modification in sensor circuit.

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Appendix

Characteristic curve for 1N4007

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PIN CONFIGURATION- AT89C51

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REFERENCE

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1. Electrical construction data book By:- Robert B. Hickey Mc-graw Hill Professional ISBN 0071373497

2. Electrical engineeriner’s portable handbook By:- Robert B. Hickey Mc-graw Hill Professional ISBN 074418202

3. Electrical Power Supply Quality By:- Roger C. Dugan Mc-graw Hill Professional ISBN 007138622X

4. Electrical Transmission and distribution handbook By:- Westinghouse Electric original From the university of michigen

5. Electrical Wiring Industrial By:- Robert L. Smith & Stepen L. Herman Thomson delnear learning publication ISBN 1401851541

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