Motors and Generators:

        Motors and generators are electromechanical devices which
perform important functions in electrical and electronic applications,
and both may be called Transducers. A transducer is a device
which converts energy from one form to another. In the case of motors
and generators, this energy is either electrical or mechanical. 
Generators are Input transducers since a generator converts
nonelectric (mechanical) energy into electric energy. Motors are
Output transducers since they convert electric energy into
mechanical energy.

        The mechanical energy supplied to the input of a generator
is often from some type of Turbine. A turbine is a type of
rotary engine that provides rotational mechanical motion as a result
of some type of fluid pressure. The water pressure of running water
represents mechanical (kinetic) energy. The turbine blades transmit
the energy to the shaft which rotates. Thus, a rotational mechanical
force is produced which can be used as the imput to a generator.
This principle is used to produce electricity in large hydroelectric
plants. The mechanical energy in these giant plants is supplied by
natural water sources such as rivers, waterfalls and dams. The 
turbines drive gigantic generators which produce electricity for 
commercial and industrial use.

        Generators produce voltages by Magnetoelectric Induction
These voltages, if applied to a  complete circuit, will cause an 
electric current to flow. When a wire conductor moves through a magnetic
field in such a way as to cut across the magnetic lines of force, a
voltage is Induced in the wire. Voltage generated by induction
is proportional to the number of flux lines cut per second. This voltage
is the Greatest when the conductor moves At Right Angles (90
degrees) to the magnetic field. The voltage is Zero when the 
conductor moves Parallel to the magnetic field. Due to the
rotation of the generator this greatest and zero occurs twice each
cycle, first of one polarity, then the opposite polarity, Since the
conductor is a complete loop through the magnetic field of the generator.

        The magnitude of the output voltage of a generator is determined
by, the speed of the conductors passing through the magnetic field, the
strength of the field, and the number of conductors moving through the
field. All three of these factors determine the number of flux lines cut
per unit of time. It should be remembered that a voltage is generated
by induction when the conductor and field move relative to each other. 
This means that either the field may remain stationary while the conductors
move, or the conductors may remain stationary while the field moves.

        The output voltage of any generator is taken from the Armature
windings. In the generator, the armature is attached to the rotating
shaft. The rotating assembly including the armature windings is called
Rotor. The emf induced in the armature windings can be connected
to an external circuit which will permit a current to flow. Various
arrangements used to supply the voltage to an external circuit will
be discussed separately (ac-dc, shunt, series, compound, and others).

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