DC Generator working principle
DC Generator working principle
An electrical generator is a device that converts mechanical
energy to electrical energy, generally using electromagnetic induction.
The source of mechanical energy may be a reciprocating or turbine steam
engine, water falling through a turbine or waterwheel, an internal
combustion engine, a wind turbine, a hand crank, or any other source of
mechanical energy.
The Dynamo was the first
electrical generator capable of delivering power for industry. The
dynamo uses electromagnetic principles to convert mechanical rotation
into an alternating electric current. A dynamo machine consists of a
stationary structure which generates a strong magnetic field, and a set
of rotating windings which turn within that field. On small machines the
magnetic field may be provided by a permanent magnet; larger machines
have the magnetic field created by electromagnets.
The energy conversion in generator is based on the principle of the production of dynamically induced e.m.f. Whenever a conductor cuts magneticic flux , dynamically induced e.m.f is produced in it according to Faraday's Laws of Electromagnetic induction.This e.m.f causes a current to flow if the conductor circuit is closed. Hence, two basic essential parts of an electrical generator are (i) a magnetic field and (ii) a conductor or conductors which can so move as to cut the flux.
The energy conversion in generator is based on the principle of the production of dynamically induced e.m.f. Whenever a conductor cuts magneticic flux , dynamically induced e.m.f is produced in it according to Faraday's Laws of Electromagnetic induction.This e.m.f causes a current to flow if the conductor circuit is closed. Hence, two basic essential parts of an electrical generator are (i) a magnetic field and (ii) a conductor or conductors which can so move as to cut the flux.
Generator Construction:
Simple loop generator is having a single-turn
rectangular copper coil rotating about its own axis in a magnetic field
provided by either permanent magnet or electro magnets.In case of without commutator the two ends of the coil are joined to slip rings
which are insulated from each other and from the central shaft.Two
collecting brushes ( of carbon or copper) press against the slip
rings.Their function is to collect the current induced in the coil. In
this case the current waveform we obtain is alternating current ( you
can see in fig). In case of with commutator the slip rings are replaced by split rings.In this case the current is unidirectional.
Components of a generator:
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.
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.
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).
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.
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.
Brushes:The
brushes are carbon blocks that maintain contact 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.
How DC generator works?
The commutator rotates with the loop of wire just as the slip rings
do with the rotor of an AC generator. Each half of the commutator ring
is called a commutator segment and is insulated from the other half.
Each end of the rotating loop of wire is connected to a commutator
segment. Two carbon brushes connected to the outside circuit rest
against the rotating commutator. One brush conducts the current out of
the generator, and the other brush feeds it in. The commutator is
designed so that, no matter how the current in the loop alternates, the
commutator segment containing the outward-going current is always
against the "out" brush at the proper time. The armature in a large DC
generator has many coils of wire and commutator segments. Because of the
commutator, engineers have found it necessary to have the armature
serve as the rotor(the rotating part of an apparatus) and the field
structure as the stator (a stationary portion enclosing rotating parts)
