assignment 1

A DCgenerator can be used as a DC motor without any changes being made to itsstructure 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-poleDC machine.

A DC machine has two basic parts stator and rotor. There areother basic constructional parts of a DC machine Yoke: Is theouter frame of a dc machine. It is made of steel or iron. It providesmechanical strength to the whole assembly but also carries the magneticflux produced by the field winding.Poles and pole shoes: Poles are joined to the yoke with the help of bolts or welding.

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Theycarry field winding and pole shoes are fastened to them. Field winding: They are usually made of copper. Field coils are placed on each poleand are connected in series. They are wound in a way that when energized, theyform alternate North and South poles. Armature core: is the rotor of the machine, Its cylindrical in shape with slots tocarry 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 wavewinding.

Double layer lap or wave windings are generally used.Commutator and brushes: Physical connection to the armature winding is made through acommutator-brush arrangement. What the commutator does is it collects thecurrent generated in armature conductors. A commutator consists of a set ofcopper parts which are insulated from each other.

The number of segments isequal 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 keepingthe physical contact to collect or supply the current.The generator is driven by its engine in thecorrect direction at its rated speed. Then DC field current issupplied to its field winding through the brush and slip ringarrangements.

This produces a very strong magnetic flux through the poles.Since the poles are rotating, the magnetic field is also rotating. The armaturewindings in the stator windings cut the flux of the rotating poles. So thenelectricity is produced in the stator winding. The frequency of the electricpower is kept constant by keeping the generator speed constant.Main parts of the alternator consists of a stator and rotor.

But unlikeother the other machines the field exciters are rotating and the armature coilis stationary.Stator:Unlike with a DC machine stator, an alternator is not meant to serve path formagnetic flux, instead it is used to hold the armature winding. The stator coreis made up of lamination of steel alloys or magnetic iron to reduce currentlosses.Rotor:  There are two types ofrotor used in an AC generatorSalient poletype: Salient pole type rotors are used in lower speed AC generator.

This typeof rotor consists of large number of silent poles attached to a magnetic wheel.These poles are also laminated to minimize the current losses. AC generatorsusing this motor are sort in length but large in diameter.Cylindrical type:Cylindrical type rotors are used in higher speed alternators and especially inturbo alternators. This type of rotor has a solid steel cylinder with slotsalong its outer edges. The slots are used for field windings.Itis more complex than it seems if you look into it in depth, but in simple formsolar cells convert the sun’s energy into electricity. It relies on thephotoelectric effect, which is the ability of matter to emit electrons when alights is shone upon it.

One of the main materials used is Silicon, it is whatis known as a semi-conductor, meaning that it shares some of the properties ofmetals and some of those of an electrical insulator, which makes it perfect forthe 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 largerscale provide heating and electricity to houses when fitted onto the roof,which saves money in the long run after usually paying for themselves afterroughly 14 years.  A primary cell or battery is one that cannot easily be recharged after one use, and arediscarded following discharge. Most primary cells utilize electrolytes that arecontained within absorbent material or a separator,and are therefore termed dry cells.A secondary cell or battery is one thatcan be electrically recharged after use to their original pre-dischargecondition, by passing current through the circuit in the opposite direction tothe current during discharge. The imagine below shows the recharging process.

Cells that are essentially utilized as primary cells, but are recharged afteruse rather than being discarded. Examples of these types of secondary cells primarily includeportable consumer electronics and electric vehicles. The table below shows the pros and cost to primaryand secondary batteries. I would personally say although primary batteries havethere uses secondary batteries are overall the betterchoice.


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