A.C. generators or alternators
Electrical motors and generators are machines which either convert electrical energy inputs into forces or applied kinetic energy inputs into electrical energy. In principle, any electrical generator can also be operated as a motor and vice-versa. In practice they will often be optimised for one application or the other.
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.A very simple AC generator consists of a permanent magnet that rotates inside a coil in such a way that the N-pole and S-pole alternate as seen from the coil The value of the voltage generated depends on-
the number of turns in the coil.
strength of the field.
the speed at which the coil or magnetic field rotates
A hand-cranked generator can be used to generate voltage to turn a motor. This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy.
WORKING PRINCIPLE
A.C Generator works on the principle of electromagnetic induction (motional emf). In generator an induced emf is produced by rotating a coil in a magnetic field. The flux linking the coil changes continuously hence a continuous fluctuating emf is obtained.
CONSTRUCTION
A.C Generator consists of the following parts.
Powerful field magnet with concave poles.
Armature:
It is a rectangular coil of large number of turns of wire wound on laminated soft-iron core of high permeability and low hysteresis loss.
Slip rings:
The ends of the coil are joined to two separate copper rings fixed on the axle (S1 & S2).
Carbon brushes:
Two carbon brushes remain pressed against each of the rings which form the terminals of the external circuit.
As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil and that electric power being used is converted to the mechanical power to drive the load.
As in the DC motor case, a current is passed through the coil, generating a torque on the coil. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave. It is called a synchronous motor. More common is the induction motor, where electric current is induced in the rotating coils rather than supplied to them directly.
One of the drawbacks of this kind of AC motor is the high current which must flow through the rotating contacts. Sparking and heating at those contacts can waste energy and shorten the lifetime of the motor. In common AC motors the magnetic field is produced by an electromagnet powered by the same AC voltage as the motor coil. The coils which produce the magnetic field are sometimes referred to as the "stator", while the coils and the solid core which rotates is called the "armature". In an AC motor the magnetic field is sinusoidally varying, just as the current in the coil varies.
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.A very simple AC generator consists of a permanent magnet that rotates inside a coil in such a way that the N-pole and S-pole alternate as seen from the coil The value of the voltage generated depends on-
the number of turns in the coil.
strength of the field.
the speed at which the coil or magnetic field rotates
A hand-cranked generator can be used to generate voltage to turn a motor. This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy.
WORKING PRINCIPLE
A.C Generator works on the principle of electromagnetic induction (motional emf). In generator an induced emf is produced by rotating a coil in a magnetic field. The flux linking the coil changes continuously hence a continuous fluctuating emf is obtained.
CONSTRUCTION
A.C Generator consists of the following parts.
Powerful field magnet with concave poles.
Armature:
It is a rectangular coil of large number of turns of wire wound on laminated soft-iron core of high permeability and low hysteresis loss.
Slip rings:
The ends of the coil are joined to two separate copper rings fixed on the axle (S1 & S2).
Carbon brushes:
Two carbon brushes remain pressed against each of the rings which form the terminals of the external circuit.
As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil and that electric power being used is converted to the mechanical power to drive the load.
As in the DC motor case, a current is passed through the coil, generating a torque on the coil. Since the current is alternating, the motor will run smoothly only at the frequency of the sine wave. It is called a synchronous motor. More common is the induction motor, where electric current is induced in the rotating coils rather than supplied to them directly.
One of the drawbacks of this kind of AC motor is the high current which must flow through the rotating contacts. Sparking and heating at those contacts can waste energy and shorten the lifetime of the motor. In common AC motors the magnetic field is produced by an electromagnet powered by the same AC voltage as the motor coil. The coils which produce the magnetic field are sometimes referred to as the "stator", while the coils and the solid core which rotates is called the "armature". In an AC motor the magnetic field is sinusoidally varying, just as the current in the coil varies.
