assignment 1

A DC
generator can be used as a DC motor without any changes being made to its
structure and vice versa is also possible. Therefore a DC generator or a DC motor could be termed as a DC machine.

figure above shows details of a 4-pole
DC machine. A DC machine has two basic parts stator and rotor. There are
other basic constructional parts of a DC machine

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Yoke: Is the
outer frame of a dc machine. It is made of steel or iron. It provides
mechanical strength to the whole assembly but also carries the magnetic
flux produced by the field winding.

Poles and pole shoes: Poles are joined to the yoke with the help of bolts or welding. They
carry field winding and pole shoes are fastened to them.

Field winding: They are usually made of copper. Field coils are placed on each pole
and are connected in series. They are wound in a way that when energized, they
form alternate North and South poles.

Armature core: is the rotor of the machine, Its cylindrical in shape with slots to
carry armature windings.

Armature winding: are usually a former wound copper coil which rests in armature slots.
Armature winding can be wound by one of the two methods, lap winding or wave
winding. Double layer lap or wave windings are generally used.

Commutator and brushes: Physical connection to the armature winding is made through a
commutator-brush arrangement. What the commutator does is it collects the
current generated in armature conductors. A commutator consists of a set of
copper parts which are insulated from each other. The number of segments is
equal to the number of armature coils. Brushes made from carbon or graphite.
They rest on commutator parts and slide on them when the commutator rotates keeping
the physical contact to collect or supply the current.

The generator is driven by its engine in the
correct direction at its rated speed. Then DC field current is
supplied to its field winding through the brush and slip ring
arrangements. This produces a very strong magnetic flux through the poles.
Since the poles are rotating, the magnetic field is also rotating. The armature
windings in the stator windings cut the flux of the rotating poles. So then
electricity is produced in the stator winding. The frequency of the electric
power is kept constant by keeping the generator speed constant.

Main parts of the alternator consists of a stator and rotor. But unlike
other the other machines the field exciters are rotating and the armature coil
is stationary.

Stator:
Unlike with a DC machine stator, an alternator is not meant to serve path for
magnetic flux, instead it is used to hold the armature winding. The stator core
is made up of lamination of steel alloys or magnetic iron to reduce current
losses.

Rotor:  There are two types of
rotor used in an AC generator

Salient pole
type: Salient pole type rotors are used in lower speed AC generator. This type
of rotor consists of large number of silent poles attached to a magnetic wheel.
These poles are also laminated to minimize the current losses. AC generators
using this motor are sort in length but large in diameter.

Cylindrical type:
Cylindrical type rotors are used in higher speed alternators and especially in
turbo alternators. This type of rotor has a solid steel cylinder with slots
along its outer edges. The slots are used for field windings.

It
is more complex than it seems if you look into it in depth, but in simple form
solar cells convert the sun’s energy into electricity. It relies on the
photoelectric effect, which is the ability of matter to emit electrons when a
lights is shone upon it. One of the main materials used is Silicon, it is what
is known as a semi-conductor, meaning that it shares some of the properties of
metals and some of those of an electrical insulator, which makes it perfect for
the use of solar cells. They can be used with for a number of different things,
some of the more popular applications are to power calculators and on a larger
scale provide heating and electricity to houses when fitted onto the roof,
which saves money in the long run after usually paying for themselves after
roughly 14 years.

 

 A primary cell or battery is one that cannot easily be recharged after one use, and are
discarded following discharge. Most primary cells utilize electrolytes that are
contained within absorbent material or a separator,
and are therefore termed dry cells.

A secondary cell or battery is one that
can be electrically recharged after use to their original pre-discharge
condition, by passing current through the circuit in the opposite direction to
the current during discharge. The imagine below shows the recharging process.
Cells that are essentially utilized as primary cells, but are recharged after
use rather than being discarded. Examples of these types of secondary cells primarily include
portable consumer electronics and electric vehicles. The table below shows the pros and cost to primary
and secondary batteries. I would personally say although primary batteries have
there uses secondary batteries are overall the better
choice.

x

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