368686365-report-on-dc-generator.docx 6a4a4l

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INDEX INTRODUCTION............................................................ 5 MATERIALS USED IN PROJECT...................................... 6 WORKING PRINCIPLE.................................................... 7 HISTORY........................................................................ 8 IMAGE OF PROJECT...................................................... 9 PRECAUTIONS............................................................. 10 GENERAL COPONENTS.................................................11 GENERAL PARTS.......................................................... 12 TYPES OF DC GENERATOR........................................... 13 USES OF DC GENERATOR............................................ 14 APPLICATIONS............................................................. 15 REFERENCE................................................................. 16 CONCLUSION.............................................................. 17

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INTRODUCTION WHAT IS A GENERATOR? Generator or Dynamo is a device for converting mechanical energy into electrical energy. In the simplest form of dynamo, a suitable conductor, in the form of a coil is rotated between the poles of a field magnet. The mechanical energy of the rotation is thus converted into electrical energy in the form of a current in the armature.

What will we do in this project? The project has a DC motor. We know that we can connect DC motor to a battery and the motor rotates. We will use the same motor to generate electricity. That means, if we rotate the shaft of the motor by hand, the armature will spin between magnetic poles inside the motor. This will produce electricity and current will start flowing in the armature. As we connect LED to the points of the motor, the current flows in the circuit and LED glows. We will rotate shaft of the motor using large pulley and a small pulley connected to the motor.

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Materials used in project 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

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Wooden board Plastic pulley Wooden batten Bolt and nuts DC motor Locking stripe for fixing motor Rubber band Foam pieces with both sided tape Screw for fitting LED(to be used as bulb) Folding straw Wire pieces washer

Working principle There are two types of generator, one is ac generator and other is dc generator. Whatever may be the types of generator, it always converts mechanical power to electrical power. An AC generator produces alternating current. A DC generator produces direct current. Both of these generators produce electrical power, based on same fundamental principle of Faraday’s law of electromagnetic induction. According to Faraday’s laws of electromagnetic induction, whenever a conductor is placed in a varying magnetic field ,an emf (electromotive force) gets induced in the conductor. The magnitude of induced emf can be calculated from the emf equation of dc generator. If the conductor is provided with the closed path, the induced current will circulate within the path. In a DC generator, field coils produce an electromagnetic field and the armature conductors are rotated into the field. Thus, an electromagnetically induced emf is generated in the armature conductors. The direction of induced current is given by Fleming’s right hand rule. According to Fleming’s right hand rule, the direction of induced current changes whenever the direction of motion of the conductor changes. Let’s consider an armature rotating clockwise and a conductor at the left is moving upward. When the armature completes a half rotation, the direction of motion of that particular conductor will be reversed to downward. Hence, the direction of current in every armature conductor will be alternating. You will know how the direction of the induced current is alternating in an armature conductor. But with a split ring commutator, connections of the armature conductors also gets reversed when the current reversal occurs. And therefore, we get unidirectional current at the terminals.

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HISTORY Before the connection between magnetism and electricity was discovered, electrostatic generators were invented. They operated on electrostatic principles, by using moving electrically charged belts, plates, and disks that carried charge to a high potential electrode. The charge was generated using either of two mechanisms: electrostatic induction or the triboelectric effect. Such generators generated very high voltage and low current. Because of their inefficiency and the difficulty of insulating machines that produced very high voltages, electrostatic generators had low power ratings, and were never used for generation of commercially significant quantities of electric power. Their only practical applications were to power early X-ray tubes, and later in some atomic particle accelerators.

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IMAGE OF PROJECT

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PRECAUTIONS 1. You should always keep your work area clean and well lit. 2. All motors include many small parts; keep very young children away from your work area. 3. Motors spin very fast; always wear safety goggles. 4. Super Glue, provided with most of the kits, is “instant bonding”. Point tube away from face and body. Do not squeeze while opening. 5. The T-pin and pushpin are sharp, be careful not to poke yourself. 6. Do not leave the motor unattended. 7. If you leave the battery shorted for a long period of time it may rupture or even explode. 8. Do not exceed 12 Volts to power the motors. You may get an electric shock. High voltages may also cause parts to overheat and create a fire. 9. If the current flowing through the transistor is big, it may get very hot. Do not touch it to prevent burns. 10. The soldering iron gets very hot! Be very careful with this tool, as it is easy to burn yourself with it. 11. Health hazard warning: Solder may contain lead. It is not suitable for small children.

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Generator components A DC generator consist of the following components 1. Rotor: In its simplest form, the rotor consists of a single loop of wire made to rotate within a magnetic field. In practice, the rotor usually consists of several coils of wire wound on an armature.

2. Armature: The armature is a cylinder of laminated iron mounted on an axle. The axle is carried in bearings mounted in the external structure of the generator. Torque is applied to the axle to make the rotor spin.

3. Coil: Each coil usually consists of many turns of copper wire wound on the armature. The two ends of each coil are connected either to two slip rings (AC) or two opposite bars of a split-ring commutator (DC).

4. Stator: The stator is the fixed part of the generator that supplies the magnetic field in which the coils rotate. It may consist of two permanent magnets with opposite poles facing and shaped to fit around the rotor. Alternatively, the magnetic field may be provided by two electromagnets.

5. Field electromagnets: Each electromagnet consists of a coil of many turns of copper wire wound on a soft iron core. The electromagnets are wound, mounted and shaped in such a way that opposite poles face each other and wrap around the rotor.

6. Brushes: The brushes are carbon blocks that maintain with the ends of the coils via the slip rings (AC) or the split-ring commutator (DC), and conduct electric current from the coils to the external circuit.

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GENERAL PARTS

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TYPES OF DC GENERATOR In some DC generators, the direct current needed for the electromagnets that make up the field structure comes from an outside source, just as it does in most AC generators. These DC generators are called separately excited generators. Many other DC generators use part of the direct current they produce to operate their own electromagnets. These generators are called self-excited generators. A self-excited DC generator depends on residual magnetism--that is, a small amount of magnetism remains in the electromagnets after the generator is shut off. Without this residual magnetism, it would be impossible to start a self-excited generator once it had stopped. The direct current needed for a self-excited generator's electromagnets can be drawn from its armature by means of three different connections: Shunt, Series and Compound, a combination of shunt and series connections. The type of generator used for a certain task depends on the amount of voltage control required. For example, a DC generator used to charge a battery needs only simple voltage control. It might be a shunt generator. A DC generator that supplies electricity for a enger elevator needs more complicated voltage control. It would be a separately excited generator. 13

USES OF DC GENERATOR Many DC generators are driven by AC motors in combinations called motor-generator sets. This is one way of changing alternating current to direct current. Factories that do electroplating and those that produce aluminum, chlorine, and some other industrial materials need large amounts of direct current and use DC generators. So do locomotives and ships driven by diesel-electric motors. Because commutators are complex and costly, many DC generators are being replaced by AC generators combined with electronic rectifiers. Rectifiers are devices that let current flow in one direction only. They permit use of simpler, more rugged AC generators, even when DC is required.

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APPLICATIONS The applications of the various types of DC Generators are as follows: Separately Excited DC Generators  Separately excited DC Generators are used in laboratories for testing as they have a wide range of voltage output.  Used as a supply source of DC motors.  Shunt wound Generators  DC shunt wound generators are used for lighting purposes.  Used to charge the battery.  Providing excitation to the alternators.  Series Wound Generators  DC series wound generators are used in DC locomotives for regenerative braking for providing field excitation current.  Used as a booster in distribution networks.  Over compounded cumulative generators are used in lighting and heavy power supply.  Flat compounded generators are used in offices, hotels, homes, schools, etc.  Differentially compounded generators are mainly used for arc welding purpose.

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REFERENCES 1. GOOGLE 2. WIKIPEDIA 3. CIRCUITGLOBE 4. PREZI 5. HUNKER 6. ENIQUEST

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CONCLUSION The invention of the DC generator made our life easy. But the fact that the commutators are complex and cost a lot of money, a lot of DC generators have been replaced by a modified AC generators which is more economical. The modification to the AC generator is done by adding Rectifiers that makes the current flow in one direction only as I mentioned before. I hope that more studies will be carried out in the future to reduce the cost of the commutators therefore reduce the cost of the DC generator.

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