Anzeige
Anzeige
Anzeige
Nächste SlideShare
12th CBSE Physics Project AC Generator
1 von 14
Anzeige

### A. c. generator by sujay class 12th

1. PHYSICS PROJECT UNDERTHEGUIDANCEOF: SUBMITTEDBY: MR. D.P. SRIVASTAVA SUJAY KUMAR LAL ROLL NO : CLASS: 12th BATCH: 2015-16
2. CERTIFICATE This is to certify that Master Sujay Kumar Lal student of class 12 of Central Academy Senior Secondary School successfully completed his project under my guidance. This project is submitted for evaluation as a part of CBSE curriculum examination for year 2015- 16. TEACHER PRINCIPAL MR. D.P. SRIVASTAVA Mrs. MALA SAXENA
3. ACKNOWLEDGEMENT I have taken efforts in this project. However, it would not have been possible without the kind support of my family & friends. I would like to extend my sincere thanks to all of them. I am highly indebted to the teacher incharge Mr. D.P. Srivastava for her guidance and constant supervision as well as for providing necessary information regarding the project and also for her support in completing the project. I would like to express my gratitude towards my parents for their kind co-operation and encouragement which help me in the completion of this project. My thanks and appreciation also go to my classmates in developing the project and to the people who have helped me out with their abilities. THANK YOU
4. AC GENERATOR What is Ac generator? The Alternating Current Generator, an electric generator, or dynamo, is a device which converts mechanical energy into electrical energy. The simplest practical generator consists of a rectangular coil rotating in a uniform magnetic field. The magnetic field is usually supplied by a permanent magnet. Principle : A.C. generators or alternators (as they are usually called) operate on the same fundamental principles of electromagnetic induction as D.C. generators. Alternating voltage may be generated by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. The value of the voltage generated depends on-
5.  the number of turns in the coil.  strength of the field.  the speed at which the coil or magnetic field rotates. Components of AC Generator  Field  Armature  Prime mover  Rotor  Stator  Slip ring Field: The field in an AC generator consists of coils of conductors within the generator that receive a voltage from a source. (called excitation) and produce a magnetic flux. The magnetic flux in the field cuts the armature to produce a voltage. This voltage is ultimately the output voltage of the AC generator.
6. Armature: The armature is the part of an AC generator in which voltage is produced. This component consists of many coils of wire that are large enough to carry the full- load current of the generator. Prime Mover: It is the component that is used to drive the AC generator. The prime mover maybe any type of rotating machine, such as a diesel engine, a steam turbine, or a motor. Rotor: The rotor of an AC generator is the rotating component of the generator, The rotor is driven by the generator’s prime mover, which may be a steam turbine, gas turbine, or diesel engine. Stator: The stator of an AC generator is the part that is stationary (refer to Figure 1). Like the rotor, this component may be the armature or the
7. field, depending on the type of generator. The stator will be the armature if the voltage output is generated there; the stator will be the field if the field excitation is applied there. Slip Rings: Slip rings are electrical connections that are used to transfer power to and from the rotor of an AC generator. Working The working principle of an alternator or AC generator is similar to the basic working principle of a DC generator.
8. Above figure helps in understanding how an alternator or AC generator works. According to the Faraday's law of electromagnetic induction, whenever a conductor moves in a magnetic field EMF gets induced across the conductor. If the close path is provided to the conductor, induced emf causes current to flow in the circuit. Now, see the above figure. Let the conductor coil ABCD is placed in a magnetic field. The direction of magnetic flux will be form N pole to S pole. The coil is connected to slip rings, and the load is connected through brushes resting on the slip rings. Now, consider the case 1 from above figure. The coil is rotating clockwise, in this case the direction of induced current can be given by Fleming's right hand rule, and it will be along A-B-C-D. As the coil is rotating clockwise, after half of the time period, the position of the coil will be as in second case of above figure. In this
9. case, the direction of the induced current according to Fleming's right hand rule will be along D-C-B-A. It shows that, the direction of the current changes after half of the time period, that means we get an alternating current.
10. Losses in Ac generator The load current flows through the armature in all AC generators. Like any coil, the armature has some amount of resistance and inductive reactance. The combination of these make up what is known as the internal resistance, which causes a loss in an AC generator. When the load current flows, a voltage drop is developed across the internal resistance. This voltage drop subtsracts from the output voltage and, therefore, represents generated voltage and power that is lost and not available to the load. The voltage drop in an AC generator can be found using Equation- Voltage drop = IaRa + IaXla Where. Ia = armature current Ra = armature resistance XLa = armature inductive reactance
11. The three losses found in an AC generator are:  Internal voltage drops due to the internal resistance and impedance of the generator  Hysteresis losses  Mechanical losses HysteresisLosses– Hysteresis losses occur when iron cores in an AC generator are subject to effects from a magnetic field. The magnetic domains of the cores are held in alignment with the field in varying numbers, dependent upon field strength. The magnetic domains rotate, with respect to the domains not held in alignment, one complete turn during each rotation of the rotor. This rotation of magnetic domains in the iron causes friction and heat. The heat produced by this
12. friction is called magnetic hysteresis loss. Mechanical Losses- Rotational or mechanical losses can be caused by bearing friction, brush friction on the commulator, and air friction (called windage), which is caused by the air turbulence due to armature rotation. Careful maintenance can be instrumental in keeping bearing friction to a minimum. Clean bearings and proper lubrication are essential to the reduction of bearing friction. Brush friction is reduced by ensuring: proper brush seating, proper brush use, and maintenance of proper brush tension. A smooth and clean commutator also aids in the reduction of brush friction. In very large generators, hydrogen is used within the generator for cooling; hydrogen, being less dense than air, causes less windage losses than air.
13. Efficiency - Efficiency of an AC generator is the ratio of the useful power output to the total power input. Because any mechanical process experiences some losses, no AC generators can be 100 percent efficient. Efficiency of an AC generator can be calculated using Equation. Efficiency = 𝑂𝑢𝑡𝑝𝑢𝑡 𝐼𝑛𝑝𝑢𝑡 x 100