dc_machines_ac_machines Seminar

[born_for seminars]

ABSTRACT
The electrical machines deals with the energy transfer either from mechanical to electrical or electrical to mechanical form. This process is called electro mechanical energy conversion. These electrical machines are designed for various applications because electrical energy is easily adaptable for all human needs and interests in an economic and efficient manner. At the same time electrical energy can be easily controlled and is pollution free at the consumer premises.
The different types involved in electrical machines is

(1) DC MACHINES
(2) AC MACHINES
DC MACHINE:
Depending up on these machines how the field winding is connected to the armature is divided into 3 types. They are (1) shunt (2) series (3) compound. Depending up on these types we shall see the various applications and how we should increase our living standards. These machines are also known as direct type machines.
AC MACHINES
These are further classified as transformers, synchronous machines, inductions and ac commutator machines. Now we shall see the various applications and importance of these machines in detail. This machine is also known as alternating type machines.
Transformers are the very important devices in power system for stepping up and stepping down the voltage. Because at high voltage transmission is efficient for sending from generating end to receiving end
Now a days we are seeing that the extension range of computers, this is because of electrical machinery. With out electrical machinery a single computer will not work. So here we shall see what is the importance of electrical machinery depending up on various types and applications.

INTRODUCTION;
To set this into historical perspective, it is recalled that Faraday conducted his experiments on electromagnetism around 1831, the basic forms of d.c. machines were in use by the 1870s and Tesla's original work on the induction motor was done around 1886.
Electricity is well known, is the most flexible form of energy that can be transported with AS from one place to another for ultimate consumption by its user. In this scenario electrical machines & transformers play a vital role whose importance cannot be overemphasized. Electrical machines are energy converting links between electrical & mechanical networks. Therefore working principles & characteristics of basic machines must be well understood by electrical engineers. In case of DC machines, the following topics must be covered: Provision of self and separate e excitation Ability of the same machine to work as a generator and a motor. Brief reference to the field of application of DC machines

CROSS SECTION VIEW OF A DC MACHINE:

ARMATURE: mainly it is divided into two parts namely (1) armature core (2) armature winding

(1) Armature core: armature core is cylindrical in shape mounted on the shaft. It consists of slots on its periphery and the air ducts to permit the airflow through armature, which serves cooling purpose.

(2) Armature winding: armature is nothing but the inter connection of the armature conductors placed in the slots provided on the armature core periphery. When the armature is rotated in case of generator, magnetic flux gets cut by armature conductor and emf gets induced in them.

COMMUTATOR: the basic nature of emf induced in the armature conductor is alternating. This needs rectification in case of dc generator, which is possible by a device called commutator.


BRUSH: brushes are stationary and resting on the surface of the commutator. Its function is to collect current from commutator and make it available to the stationary external circuit.
DC MACHINES:
These DC machines are classified into two types. They are
DC Generators
DC Motors

PRINCIPLE OF OPERATION OF GENERATORS:
All the generators work on the principle of DYNAMICALL INDUCED EMF. This principle is nothing but the “FARADAYAS LAW OF ELECTRO MAGNETIC INDUCTION”.
“When ever a conductor cuts magnetic flux, dynamically induced emf is produced in it. This emf causes a current to flow if the conductor circuit is closed”.

Key point: so generating action requires following basic components to exist,(1)The conductor or a coil.(2)the flux.(3)the relative motion between conductor and flux.