Today we will see how to make project on 'Project on AC GENERATOR for class 12th' this project is only for class 12th student and this project is belongs to 'ALTERNATING CURRENTS' in this project we will cover
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
Ø the number of turns in the coil.
Ø strength of the field.
Ø the speed at which the coil or magnetic field rotates.
Components of AC Generator
Field
Armature
Prime mover
Prime mover
Prime mover
Prime mover
Rotor
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.
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 fullload current of the generator.
Prime Mover :
It is the component that is used to drive the AC
generator. The primemover 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 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.
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 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.
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 usingEquation-
Voltage drop = IaRa + IaXla
Where.
Ia = armature current
Ra = armature resistance
XLa = armature inductive reactance
The three losses found in an AC generator are:
v Internal voltage drops due to the
internal resistance and impedance
of the generator
v Hysteresis losses
v Mechanical losses
Hysteresis Losses –
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 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.
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
BIBLIOGRAPHY
Øwww.mycbseguide.com
ØNCERT (textbook)
Øwww.google.com
Øwww.yahooanswer.com
Øwww.electricalessay.comYOU CAN WATCH OUR VIDEO
you can see our pdf also
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